feat: preprocess native argv into sentinel slices

LANGUAGE.md

@@ -34,7 +34,7 @@ roadmap and milestone history.
 - compile-time `minval!(T)` and `maxval!(T)` bounds for concrete native, C, and scalar-backed distinct integer types; the result retains `T`
 - arrays `[N]T`, inferred-count arrays `[_]T`, sentinel arrays `[N;S]T`, compile-time expression array counts, slices `[]T` / `[;S]T`, single-item pointers `@T`, many-item pointers `*T`, and sentinel many-item pointers `[*;S]T`
 - pointer mutability via `mut`, optional pointers as nullable pointers, pointer arithmetic for many-item pointers, postfix dereference `^`, and trapping optional unwrap `?`
-- pointer-to-array `.len`, indexing, slicing, `.ptr` on slices and pointers-to-arrays, implicit address-taking for array-variable slices, and pointer/slice sentinel weakening
+- pointer-to-array `.len`, indexing, slicing, `.ptr` on slices and pointers-to-arrays, implicit address-taking for array-variable slices, pointer/slice sentinel weakening, and checked explicit sentinel slicing `base[start..end;S]`
 - `ptrcast!(ptr)` infers its complete pointer result from context; `ptrcast!(P, ptr)` supplies `P` explicitly; both change the child type, then permit only ordinary implicit pointer conversions to the requested target
 - unsafe `constcast!(value)` for restoring mutability to pointers, optional pointers, and slices without changing their child type or shape
 - UTF-8 string literals as immutable pointers to static zero-terminated byte arrays, supporting `\\`, `\"`, `\n`, `\r`, `\t`, `\0`, and `\xNN` escapes, plus raw backtick multiline strings
@@ -44,10 +44,32 @@ roadmap and milestone history.
 - compiler-reordered native structs with fields laid out by decreasing alignment (declaration order breaks ties and remains the reflection/diagnostic order), opaque nominal records with `Name :: opaque`, complete source-order `c_struct { ... }`, keyed record literals, native untagged unions, and native tagged unions `union(Enum)` / `union(enum)`
 - named native struct fields may declare defaults with `field T = expression`; keyed literals use defaults for omitted fields and explicit initializers override them
 - void-payload tagged-union variants, anonymous struct payloads, contextual `.variant`, `.variant{payload}`, and `.variant{field = value}` construction
-- native sum composition with `A | B` for unbacked enums and tagged unions, optionally grouped as `(A | B)`, using program-global `u16` variant ids
+- native sum composition with `A | B` for unbacked enums and tagged unions, optionally grouped as `(A | B)`, using program-global `u16` variant ids; parenthesized types allow newlines after `(`, before `)`, and on either side of `|`, including in aliases and fallible signatures
 - fallible channel types `T ! E`, where `E` is a native enum, native struct, tagged union, or supported sum composition; `void ! E` functions complete successfully on fallthrough, and void-success `catch` handlers may fall through without `yield`
 - bodyful local functions and root `main` may write `T!` to infer a specialization-local error channel from propagated `try` expressions and concretely typed error returns; inference composes only existing named error types, never synthesizes variants, and requires at least one inferred error
 
+#### checked sentinel slicing
+
+`base[start..end;S]` constructs a sentinel slice `[;S]T` without copying elements.
+The sentinel `S` must be a compile-time integer representable by the source element type `T`;
+the result retains the source's element mutability. Bounds use `usize`, as in ordinary slicing.
+`start` defaults to zero; `end` may be omitted for arrays, pointers-to-arrays, and slices, where
+it defaults to the logical length. Many-item pointers, including sentinel pointers, always
+require an explicit end: `pointer[..count;0]`.
+
+The result contains elements `[start, end)` and excludes the sentinel at `end`.
+Before constructing it, runtime checks require ordered in-range bounds, a readable endpoint,
+and `base[end] == S`; failure traps. For a bounded source without a sentinel, `end` must be
+strictly less than its length. A sentinel source permits `end == len`, reading its stored
+sentinel. A many-item pointer has no length to check: the caller must provide valid memory
+through the endpoint, and the endpoint value is still checked. Comptime evaluation enforces
+the same endpoint and sentinel requirements and diagnoses failures.
+
+Ordinary `base[start..end]` slicing keeps its existing bounds rules and preserves a source
+sentinel only when the end bound is omitted. Explicit sentinel slicing can assert a different
+sentinel only when the actual endpoint matches it; it never adds a terminator or restores
+mutability.
+
 #### distinct types
 
 `Name :: distinct T` creates a nominal identity and reuses `T`'s runtime representation. When
@@ -266,7 +288,8 @@ exactly once. Bare functions named `memcopy` or `memset` remain ordinary user fu
 - `std/arraylist` generic `ArrayList(T)` with direct `items` slice access, explicit capacity, allocator ownership, fallible reserve/append, clear, and deinit
 - `std/meta` reflection records plus `EnumFieldStruct(E, Field, default ?Field)`, implemented with `struct_type!`; it produces a record with one field per native enum member in declaration order, where outer `null` means no field default
 - `std/io` explicit `Io` capabilities, provider-bound `Reader`/`Writer` handles, existing-file open/close operations, allocation-free `write_all`, and comptime-expanded writer-first `print`; formatting supports natural `{}`, byte `{s}`, decimal `{d}`, integer `{b}` / `{o}` / `{x}` / `{X}`, byte-character `{c}`, scientific float `{e}`, recursively scalar-backed distinct values, and `{{` / `}}`, with malformed formats and incompatible tuple fields rejected at comptime
-- entry points are either `main func() ...` or `main func(init process.Init) ...`; their success channel is `void`, `i32`, or `int` and may have an error channel; an unhandled entry error exits with status 1. `std/process.Init` carries startup capabilities, currently only `io`, while the system provider remains hidden inside `std/io`
+- entry points are either `main func() ...` or `main func(init process.Init) ...`; their success channel is `void`, `i32`, or `int` and may have an error channel; an unhandled entry error exits with status 1. `std/process.Init` contains exactly `io io.Io` and `args Args`, while the system provider remains hidden inside `std/io`
+- `std/process.Args` contains exactly `values [][;0]u8`; use `args.values.len` and direct indexing. Native startup scans each argument once into heap-owned slice descriptors while borrowing, not copying, the strings; index 0 is the executable name when present, and empty arguments remain empty slices. The descriptors and their borrowed views are valid until `main` returns; the native wrapper frees the descriptors on both success and error
 - `std/debug.print` is an allocation-free, failure-ignoring stderr escape hatch independent of `process.Init`
 - `std/testing` supplies fallible `expect`, expected-first `expect_equal`, and exact compile-time `expect_type`; direct calls through
   an alias of exactly `@std/testing` receive compiler-injected source locations
@@ -277,7 +300,7 @@ exactly once. Bare functions named `memcopy` or `memset` remain ordinary user fu
 - lazy semantic checking of demanded function specializations
 - static, eager runtime, mutable runtime, and deferred problematic globals with cycle diagnostics
 - demand-driven LLVM declarations for referenced foreign functions
-- root `main` may be parameterless or accept canonical `@std/process Init`; the generated C entry point obtains the hidden system I/O provider and constructs the init value
+- root `main` may be parameterless or accept canonical `@std/process Init`; the generated C entry point accepts native `argc`/`argv`, obtains the hidden system I/O provider, and constructs the init value using computed record layout. Both `Init` and `Args` must have their canonical auto-layout record shapes. Descriptor allocation is size-checked, zero-count safe, and exits with status 2 on overflow or allocation failure; parameterless `main` does not prepare arguments
 - `brolang test [root]` reuses `build.bro`, discovers only explicit test-import edges, skips the
   application entry point, and runs tests sequentially while continuing after assertion failures
 - replaceable dynamically loaded libclang C-import backend

README.md

@@ -9,8 +9,9 @@ odin build . -out:build/brolang
 ./build/prototype
 ```
 
-Programs may receive the system I/O capability explicitly. Standard-stream
-helpers bind the provider, handle, and callback; `main func() ...` remains valid.
+Programs may receive system I/O and process arguments explicitly through
+`process.Init`; `main func() ...` remains valid. Standard-stream helpers bind the
+provider, handle, and callback.
 
 ```bro
 io :: import "@std/io"
@@ -23,6 +24,16 @@ main func(init process.Init) void {
 }
 ```
 
+`Init` contains `io io.Io` and `args process.Args`. `Args.values` has type
+`[][;0]u8`: use `init.args.values.len` for the count and
+`init.args.values[index]` for a borrowed, zero-terminated argument slice.
+Index 0 is the executable name when present, and empty arguments are empty
+slices. Startup scans each native argument once and allocates only the slice
+descriptors; argument strings are never copied. The native entry wrapper owns
+the descriptors until `main` returns, freeing them on both success and error.
+An empty native argument list is supported; allocation overflow or failure exits
+with status 2. Parameterless `main` does not prepare unused arguments.
+
 Bodyless `c_func` declarations bind exact external symbols and require concrete
 types. C primitives use atomic target-dependent names and remain semantically
 distinct from exact-width Brolang primitives:

compiler/checker/checker.odin

@@ -400,6 +400,9 @@ block_reads_name :: proc(checker: ^Checker, statements: []ast.Stmt_Id, name: sym
 		case .Call, .Array, .Struct_Literal, .Slice:
 			append(&expr_stack, ..expr.args)
 			append(&expr_stack, expr.left)
+			if expr.kind == .Slice {
+				append(&expr_stack, expr.right)
+			}
 		case .Negate, .Not, .Bit_Not, .Address, .Deref, .Field, .Unwrap, .Try, .Keyed, .Enum_Literal, .Cast:
 			append(&expr_stack, expr.left)
 		case .Comptime:
@@ -743,12 +746,18 @@ comptime_slice_bytes :: proc(
 	pkg: ast.Package_Id,
 	file: ast.File_Id,
 ) -> (string, bool) {
+	if expr.right != ast.INVALID_EXPR {
+		return "", false
+	}
 	state := ct_state_make(checker, pkg, file, diagnose=false)
 	defer ct_state_destroy(&state)
 	value, flow, ok := ct_eval_slice_expr(&state, expr, 0)
 	if !ok || flow.kind != .Normal {
 		return "", false
 	}
+	if item, item_ok := types.container(state.values[value].type, &checker.module.types); item_ok && item.has_sentinel {
+		return "", false
+	}
 	return ct_value_bytes(&state, value)
 }
 
@@ -1747,16 +1756,47 @@ configure_entry_point :: proc(checker: ^Checker) {
 	if io_package == ast.INVALID_PACKAGE {
 		return
 	}
-	init_item, init_ok := types.node(&checker.module.types, parameter_type)
-	init_fields := types.fields_for(&checker.module.types, parameter_type)
-	io_field_name := symbol.intern(checker.symbols, "io")
-	if !init_ok || init_item.kind != .Struct || init_item.tuple || init_item.c_layout ||
-	   len(init_fields) != 1 || init_fields[0].name != u32(io_field_name) ||
-	   !types.equal(types.resolve_alias(init_fields[0].type, &checker.module.types), io_type) {
+	args_name := symbol.intern(checker.symbols, "Args")
+	args_type := types.resolve_alias(
+		types.find_named(&checker.module.types, u32(process_package), u32(args_name)),
+		&checker.module.types,
+	)
+	args_item, args_ok := types.node(&checker.module.types, args_type)
+	args_fields := types.fields_for(&checker.module.types, args_type)
+	values_name := symbol.intern(checker.symbols, "values")
+	argument_slice := types.slice(&checker.module.types, types.U8, false, true, 0)
+	argument_values := types.slice(&checker.module.types, argument_slice, false)
+	if !args_ok || args_item.kind != .Struct || args_item.tuple || args_item.c_layout ||
+	   len(args_fields) != 1 || args_fields[0].name != u32(values_name) ||
+	   !types.equal(types.resolve_alias(args_fields[0].type, &checker.module.types), argument_values) {
 		checker.template_diagnostics[main_template] = source.add(
 			checker.diagnostics,
 			main.span,
-			"@std/process Init must be an auto-layout record containing exactly 'io io.Io'",
+			"@std/process Args must be an auto-layout record containing exactly 'values [][;0]u8'",
+		)
+		return
+	}
+
+	init_item, init_ok := types.node(&checker.module.types, parameter_type)
+	init_fields := types.fields_for(&checker.module.types, parameter_type)
+	io_field_name := symbol.intern(checker.symbols, "io")
+	args_field_name := symbol.intern(checker.symbols, "args")
+	io_field_ok, args_field_ok := false, false
+	for field in init_fields {
+		field_type := types.resolve_alias(field.type, &checker.module.types)
+		if field.name == u32(io_field_name) && types.equal(field_type, io_type) {
+			io_field_ok = true
+		}
+		if field.name == u32(args_field_name) && types.equal(field_type, args_type) {
+			args_field_ok = true
+		}
+	}
+	if !init_ok || init_item.kind != .Struct || init_item.tuple || init_item.c_layout ||
+	   len(init_fields) != 2 || !io_field_ok || !args_field_ok {
+		checker.template_diagnostics[main_template] = source.add(
+			checker.diagnostics,
+			main.span,
+			"@std/process Init must be an auto-layout record containing exactly 'io io.Io' and 'args Args'",
 		)
 		return
 	}
@@ -2753,6 +2793,15 @@ match_inferred_type_pattern :: proc(
 				values, bound, span, diagnose, depth+1,
 			)
 		}
+		if actual_ok && actual_item.kind == .Slice {
+			if pattern_item.has_sentinel && (!actual_item.has_sentinel || pattern_item.sentinel != actual_item.sentinel) {
+				return false
+			}
+			return match_inferred_type_pattern(
+				checker, function, prefix, pattern_item.child, actual_item.child,
+				values, bound, span, diagnose, depth+1,
+			)
+		}
 	}
 	if !actual_ok || pattern_item.kind != actual_item.kind {
 		resolved := type_from_syntax(checker, pattern, function.pkg, function.file)
@@ -3786,6 +3835,9 @@ mark_expr_imports_used :: proc(checker: ^Checker, expr_id: ast.Expr_Id, file: as
 			if expr.left != ast.INVALID_EXPR {
 				append(&stack, expr.left)
 			}
+			if expr.kind == .Slice && expr.right != ast.INVALID_EXPR {
+				append(&stack, expr.right)
+			}
 		case .Negate, .Not, .Bit_Not, .Address, .Deref, .Field, .Unwrap, .Try, .Keyed, .Enum_Literal, .Cast:
 			append(&stack, expr.left)
 		case .Comptime:
@@ -5168,6 +5220,15 @@ infer_compound_expr :: proc(
 				_ = record_demand(checker, bound, types.USIZE, locals, local_types, pkg, file)
 			}
 		}
+		if expr.right != ast.INVALID_EXPR {
+			state := ct_state_make(checker, pkg, file, diagnose=false)
+			defer ct_state_destroy(&state)
+			sentinel, sentinel_ok := checked_slice_sentinel(&state, expr.right, item.child)
+			if !sentinel_ok {
+				return types.INVALID
+			}
+			return types.slice(store, item.child, item.mutable, true, u64(sentinel))
+		}
 		preserve := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
 		return types.slice(store, item.child, item.mutable, preserve, item.sentinel)
 	case .Field:
@@ -8773,6 +8834,22 @@ build_compound_expr :: proc(
 			id := source.add(checker.diagnostics, expr.span, "many-item pointer slicing requires an explicit end bound")
 			return invalid_hir_expr(checker, expr.span, id)
 		}
+		sentinel_expr := hir.INVALID_EXPR
+		sentinel := item.sentinel
+		if expr.right != ast.INVALID_EXPR {
+			state := ct_state_make(checker, pkg, file)
+			defer ct_state_destroy(&state)
+			constant, sentinel_ok := checked_slice_sentinel(&state, expr.right, item.child)
+			if !sentinel_ok {
+				return invalid_hir_expr(checker, expr.span, state.diagnostic)
+			}
+			sentinel = u64(constant)
+			sentinel_expr = add_hir_expr(checker, hir.Expr{
+				kind=.Integer, span=checker.ast_module.exprs[expr.right].span, type=item.child, integer=i64(sentinel),
+				target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+		}
 		bounds := make([]hir.Expr_Id, 2, checker.allocator)
 		bounds[0] = hir.INVALID_EXPR
 		bounds[1] = hir.INVALID_EXPR
@@ -8791,11 +8868,11 @@ build_compound_expr :: proc(
 				}
 			}
 		}
-		preserve_sentinel := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
-		result_type := types.slice(store, item.child, item.mutable, preserve_sentinel, item.sentinel)
+		preserve_sentinel := expr.right != ast.INVALID_EXPR || item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
+		result_type := types.slice(store, item.child, item.mutable, preserve_sentinel, sentinel)
 		return add_hir_expr(checker, hir.Expr{
 			kind=.Slice, span=expr.span, type=result_type, args=bounds, left=container,
-			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
+			target=hir.INVALID_REF, right=sentinel_expr, diagnostic=source.INVALID_DIAGNOSTIC,
 		})
 	case .Field:
 		if enum_type, enum_ok := enum_type_from_field_expr(checker, expr, pkg, file, true); enum_ok {

compiler/checker/comptime.odin

@@ -792,6 +792,17 @@ ct_place_get :: proc(state: ^Ct_State, place_id: Ct_Place_Id) -> (Ct_Value_Id, b
 		#partial switch elem.kind {
 		case .Index:
 			index := int(elem.index)
+			if value.kind == .Array {
+				item, ok := types.node(&state.checker.module.types, value.type)
+				if ok && item.has_sentinel && u64(index) == item.count {
+					integer := i128(item.sentinel)
+					if types.is_signed(types.resolve_alias(item.child, &state.checker.module.types), state.checker.target) {
+						integer = i128(i64(item.sentinel))
+					}
+					current = ct_add_value(state, Ct_Value{kind=.Integer, type=item.child, integer=integer})
+					continue
+				}
+			}
 			if value.kind != .Array || index < 0 || index >= len(children) {
 				return INVALID_CT_VALUE, false
 			}
@@ -963,7 +974,7 @@ ct_value_can_materialize :: proc(state: ^Ct_State, id: Ct_Value_Id, depth := 0)
 		store := &state.checker.module.types
 		slice, slice_ok := types.node(store, value.type)
 		place_id := Ct_Place_Id(value.index)
-		if !slice_ok || slice.kind != .Slice || slice.mutable || value.start != 0 ||
+		if !slice_ok || slice.kind != .Slice || slice.mutable ||
 		   place_id == INVALID_CT_PLACE || int(place_id) >= len(state.places) {
 			return false
 		}
@@ -977,7 +988,7 @@ ct_value_can_materialize :: proc(state: ^Ct_State, id: Ct_Value_Id, depth := 0)
 		}
 		root := state.values[root_id]
 		array, array_ok := types.node(store, root.type)
-		return array_ok && array.kind == .Array && u64(value.count) == array.count &&
+		return array_ok && array.kind == .Array && u64(value.start)+u64(value.count) <= array.count &&
 		       types.equal(slice.child, array.child) && ct_value_can_materialize(state, root_id, depth+1)
 	case .Range, .Array, .Struct, .Optional_Some, .Fallible:
 		for child in ct_child_slice(state, value) {
@@ -1065,7 +1076,7 @@ ct_materialize_array_slice :: proc(
 	store := &state.checker.module.types
 	slice, slice_ok := types.node(store, value.type)
 	place_id := Ct_Place_Id(value.index)
-	if !slice_ok || slice.kind != .Slice || slice.mutable || value.start != 0 ||
+	if !slice_ok || slice.kind != .Slice || slice.mutable ||
 	   place_id == INVALID_CT_PLACE || int(place_id) >= len(state.places) {
 		return hir.INVALID_EXPR, false
 	}
@@ -1079,7 +1090,7 @@ ct_materialize_array_slice :: proc(
 	}
 	root := state.values[root_id]
 	array, array_ok := types.node(store, root.type)
-	if !array_ok || array.kind != .Array || u64(value.count) != array.count ||
+	if !array_ok || array.kind != .Array || u64(value.start)+u64(value.count) > array.count ||
 	   !types.equal(slice.child, array.child) {
 		return hir.INVALID_EXPR, false
 	}
@@ -1093,7 +1104,28 @@ ct_materialize_array_slice :: proc(
 	if !ok {
 		return hir.INVALID_EXPR, false
 	}
-	return coerce_expr(state.checker, address, value.type, span), true
+	checker := state.checker
+	bounds := make([]hir.Expr_Id, 2, checker.allocator)
+	endpoints := [2]u32{value.start, value.start+value.count}
+	for integer, index in endpoints {
+		bounds[index] = add_hir_expr(checker, hir.Expr{
+			kind=.Integer, span=span, type=types.USIZE, integer=i64(integer),
+			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
+	}
+	sentinel_expr := hir.INVALID_EXPR
+	if slice.has_sentinel {
+		sentinel_expr = add_hir_expr(checker, hir.Expr{
+			kind=.Integer, span=span, type=slice.child, integer=i64(slice.sentinel),
+			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
+	}
+	return add_hir_expr(checker, hir.Expr{
+		kind=.Slice, span=span, type=value.type, args=bounds, left=address, right=sentinel_expr,
+		target=hir.INVALID_REF, diagnostic=source.INVALID_DIAGNOSTIC,
+	}), true
 }
 
 ct_materialize_value :: proc(
@@ -1223,7 +1255,7 @@ ct_materialize_value :: proc(
 			return result
 		}
 		if state.diagnostic == source.INVALID_DIAGNOSTIC {
-			state.diagnostic = source.add(checker.diagnostics, span, "only immutable full-array comptime slices can materialize as runtime memory")
+			state.diagnostic = source.add(checker.diagnostics, span, "only immutable array-backed comptime slices can materialize as runtime memory")
 		}
 		return invalid_hir_expr(checker, span, state.diagnostic, value.type)
 	case .Function:
@@ -1948,6 +1980,22 @@ ct_eval_struct_expr :: proc(state: ^Ct_State, expr: ast.Expr, expected: types.Ty
 	return ct_add_value(state, Ct_Value{kind=.Struct, type=struct_type, start=start, count=u32(len(values)), active=active_field}), ct_flow(.Normal), true
 }
 
+checked_slice_sentinel :: proc(state: ^Ct_State, id: ast.Expr_Id, child: types.Type) -> (i128, bool) {
+	checker := state.checker
+	span := checker.ast_module.exprs[id].span
+	previous_error := state.error
+	constant := eval_integer_constant_in_state(state, id, allow_bool=false)
+	state.error = previous_error
+	if constant.kind != .Value {
+		return 0, ct_fail(state, .Not_Comptime, span, "slice sentinel must be a compile-time integer")
+	}
+	representation := types.resolve_alias(child, &checker.module.types)
+	if !types.is_concrete_integer(representation) || !fits_integer_type(constant.value, representation, checker.target) {
+		return 0, ct_failf(state, .Not_Comptime, span, "slice sentinel value does not fit element type %s", type_label(checker, child))
+	}
+	return constant.value, true
+}
+
 ct_eval_slice_expr :: proc(state: ^Ct_State, expr: ast.Expr, depth: int) -> (Ct_Value_Id, Ct_Flow, bool) {
 	checker := state.checker
 	store := &checker.module.types
@@ -1958,6 +2006,7 @@ ct_eval_slice_expr :: proc(state: ^Ct_State, expr: ast.Expr, depth: int) -> (Ct_
 	container_place := INVALID_CT_PLACE
 	container_start := 0
 	container_len := 0
+	bounded := true
 	item: types.Node
 	item_ok := false
 	if base_value != INVALID_CT_VALUE && int(base_value) < len(state.values) {
@@ -1967,6 +2016,25 @@ ct_eval_slice_expr :: proc(state: ^Ct_State, expr: ast.Expr, depth: int) -> (Ct_
 			container_start = int(base.start)
 			container_len = int(base.count)
 			item, item_ok = types.node(store, base.type)
+		} else if base.kind == .Array && checker.ast_module.exprs[expr.left].kind == .Array && expr.right != ast.INVALID_EXPR {
+			item, item_ok = types.node(store, base.type)
+			container_place = ct_add_place(state, ct_add_cell(state, base_value, false), base.type, false)
+			container_len = int(base.count)
+			item.mutable = false
+		} else if base.kind == .String && expr.right != ast.INVALID_EXPR && base.index < u64(len(checker.ast_module.strings)) {
+			text := checker.ast_module.strings[base.index]
+			array_type := types.array(store, types.U8, u64(len(text)), false, true, 0)
+			children := make([]Ct_Value_Id, len(text), checker.allocator)
+			defer delete(children, checker.allocator)
+			for byte, index in transmute([]u8)text {
+				children[index] = ct_add_value(state, Ct_Value{kind=.Integer, type=types.U8, integer=i128(byte)})
+			}
+			child_start := u32(len(state.children))
+			append(&state.children, ..children)
+			array_value := ct_add_value(state, Ct_Value{kind=.Array, type=array_type, start=child_start, count=u32(len(text))})
+			container_place = ct_add_place(state, ct_add_cell(state, array_value, false), array_type, false)
+			container_len = len(text)
+			item, item_ok = types.container(base.type, store)
 		} else if base.kind == .Pointer {
 			pointer_item, pointer_ok := types.node(store, base.type)
 			array_item: types.Node
@@ -1980,6 +2048,15 @@ ct_eval_slice_expr :: proc(state: ^Ct_State, expr: ast.Expr, depth: int) -> (Ct_
 				item = array_item
 				item.mutable = pointer_item.mutable && array_item.mutable
 				item_ok = true
+			} else if pointer_ok && pointer_item.many {
+				if expr.args[1] == ast.INVALID_EXPR {
+					return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "many-item pointer slicing requires an explicit end bound")
+				}
+				container_place = Ct_Place_Id(base.index)
+				container_start = int(base.active)
+				item = pointer_item
+				item_ok = true
+				bounded = false
 			}
 		}
 	}
@@ -2031,11 +2108,31 @@ ct_eval_slice_expr :: proc(state: ^Ct_State, expr: ast.Expr, depth: int) -> (Ct_
 			end = int(integer)
 		}
 	}
-	if start < 0 || end < start || end > container_len {
+	if start < 0 || end < start || bounded && end > container_len || container_start < 0 {
 		return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime slice bounds out of range")
 	}
-	preserve_sentinel := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
-	result_type := types.slice(store, item.child, item.mutable, preserve_sentinel, item.sentinel)
+	sentinel := item.sentinel
+	if expr.right != ast.INVALID_EXPR {
+		constant, sentinel_ok := checked_slice_sentinel(state, expr.right, item.child)
+		if !sentinel_ok {
+			return INVALID_CT_VALUE, ct_flow(.Normal), false
+		}
+		if bounded && (end == container_len && !item.has_sentinel) {
+			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime sentinel slice endpoint out of range")
+		}
+		endpoint := ct_extend_place(state, container_place, Ct_Path_Elem{kind=.Index, index=u32(container_start+end)}, item.child, false)
+		value, value_ok := ct_place_get(state, endpoint)
+		if !value_ok {
+			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime sentinel slice endpoint out of range")
+		}
+		actual, actual_ok := ct_integer_value(state, value)
+		if !actual_ok || actual != constant {
+			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime slice sentinel mismatch")
+		}
+		sentinel = u64(constant)
+	}
+	preserve_sentinel := expr.right != ast.INVALID_EXPR || item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
+	result_type := types.slice(store, item.child, item.mutable, preserve_sentinel, sentinel)
 	return ct_add_value(state, Ct_Value{
 		kind=.Slice, type=result_type, index=u64(container_place),
 		start=u32(container_start+start), count=u32(end-start),
@@ -5973,7 +6070,7 @@ eval_integer_constant_in_context :: proc(
 	return eval_integer_constant_in_state(&state, expr_id, depth)
 }
 
-eval_integer_constant_in_state :: proc(state: ^Ct_State, expr_id: ast.Expr_Id, depth := 0) -> Constant {
+eval_integer_constant_in_state :: proc(state: ^Ct_State, expr_id: ast.Expr_Id, depth := 0, allow_bool := true) -> Constant {
 	if depth > 64 || expr_id == ast.INVALID_EXPR || int(expr_id) >= len(state.checker.ast_module.exprs) {
 		return Constant{kind=.Not_Constant}
 	}
@@ -5994,6 +6091,9 @@ eval_integer_constant_in_state :: proc(state: ^Ct_State, expr_id: ast.Expr_Id, d
 		}
 		return Constant{kind=.Not_Constant}
 	}
+	if !allow_bool && state.values[value].kind != .Integer {
+		return Constant{kind=.Not_Constant}
+	}
 	integer, integer_ok := ct_integer_value(state, value)
 	if !integer_ok {
 		return Constant{kind=.Not_Constant}

compiler/ir/ir.odin

@@ -86,6 +86,9 @@ Opcode :: enum u8 {
 	Store,
 	Fill,
 	Slice,
+	// Private native-entry operations: own descriptors, borrow argument strings.
+	Prepare_Args,
+	Free_Args,
 	Length,
 	Slice_Ptr,
 	Extract,

compiler/llvm/llvm.odin

@@ -20,6 +20,7 @@ Emitter :: struct {
 	builder:     strings.Builder,
 	messages:    [dynamic]Trap_Message,
 	allocator:   mem.Allocator,
+	prepares_args: bool,
 }
 
 C_Record_ABI_Kind :: enum u8 {
@@ -284,7 +285,7 @@ valid_value :: proc(
 	}
 	switch instructions[value_id].op {
 	case .Param, .Const, .Poison, .String, .Aggregate, .Null, .Optional_Some,
-	     .Load_Global, .Function_Address, .Address_Of, .Load, .Union_Tag, .Slice, .Length, .Slice_Ptr,
+	     .Load_Global, .Function_Address, .Address_Of, .Load, .Union_Tag, .Slice, .Prepare_Args, .Length, .Slice_Ptr,
 	     .Fallible_Error, .Extract, .Select, .Unwrap,
 	     .Optional_Is_Some, .Optional_Value, .Orelse,
 	     .Widen, .Sum_Widen, .Sum_Project, .C_Coerce, .C_Vararg_Promote, .Retype, .Scalar_Cast, .Pointer_Cast, .Const_Cast, .Weaken_Pointer, .Weaken_Slice, .Decay_Array_Pointer,
@@ -295,7 +296,7 @@ valid_value :: proc(
 	     .Shift_Left, .Shift_Right, .Shift_Left_Saturating, .Compare, .Call:
 		return true
 	case .Address_Global, .Alloca, .Index_Address, .Field_Address, .Orelse_Begin,
-	     .Store, .Fill, .Mem_Copy, .Mem_Set, .Trap, .Label, .Br, .Cond_Br, .Return, .Return_Void:
+	     .Store, .Fill, .Free_Args, .Mem_Copy, .Mem_Set, .Trap, .Label, .Br, .Cond_Br, .Return, .Return_Void:
 		return false
 	}
 	return false
@@ -1545,6 +1546,16 @@ emit_instruction_stream :: proc(
 			write_operand(&emitter.builder, instructions, instruction.b, instruction.type, &emitter.module.types)
 			fmt.sbprintf(&emitter.builder, ", ptr %%memset_element%d\n", instruction_index)
 			fmt.sbprintf(&emitter.builder, "  %%memset_next%d = add i64 %%memset_index%d, 1\n  store i64 %%memset_next%d, ptr %%memset_index_slot%d\n  br label %%memset_loop%d\nmemset_done%d:\n", instruction_index, instruction_index, instruction_index, instruction_index, instruction_index, instruction_index)
+		case .Prepare_Args:
+			fmt.sbprintf(&emitter.builder, "  %%v%d = call %s @bro.prepare_args(i32 ", instruction_index, llvm_type(instruction.type, &emitter.module.types))
+			write_operand(&emitter.builder, instructions, instruction.a, types.C_INT, &emitter.module.types)
+			strings.write_string(&emitter.builder, ", ptr ")
+			write_operand(&emitter.builder, instructions, instruction.b, instructions[instruction.b].type, &emitter.module.types)
+			strings.write_string(&emitter.builder, ")\n")
+		case .Free_Args:
+			fmt.sbprintf(&emitter.builder, "  %%args_data%d = extractvalue %s ", instruction_index, llvm_type(instructions[instruction.a].type, &emitter.module.types))
+			write_operand(&emitter.builder, instructions, instruction.a, instructions[instruction.a].type, &emitter.module.types)
+			fmt.sbprintf(&emitter.builder, ", 0\n  call void @free(ptr %%args_data%d)\n", instruction_index)
 		case .Slice:
 			if !valid_instruction(instructions, instruction.a) {
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid slice container")
@@ -1556,6 +1567,11 @@ emit_instruction_stream :: proc(
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid slice container")
 				continue
 			}
+			check_sentinel := instruction.b != ir.INVALID_INSTRUCTION
+			if check_sentinel && !valid_value(instructions, instruction.b, item.child, &emitter.module.types) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid slice sentinel")
+				continue
+			}
 			pointer_name := fmt.tprintf("%%v%d", instruction.a)
 			length_name := fmt.tprintf("%d", item.count)
 			if item.kind == .Array {
@@ -1597,13 +1613,25 @@ emit_instruction_stream :: proc(
 			if item.kind == .Pointer {
 				fmt.sbprintf(&emitter.builder, "  %%slice_ok%d = or i1 false, %%slice_order%d\n", instruction_index, instruction_index)
 			} else {
-				fmt.sbprintf(&emitter.builder, "  %%slice_end_ok%d = icmp ule i64 %s, %s\n", instruction_index, end_name, length_name)
+				comparison := "ult" if check_sentinel && !item.has_sentinel else "ule"
+				fmt.sbprintf(&emitter.builder, "  %%slice_end_ok%d = icmp %s i64 %s, %s\n", instruction_index, comparison, end_name, length_name)
 				fmt.sbprintf(&emitter.builder, "  %%slice_ok%d = and i1 %%slice_order%d, %%slice_end_ok%d\n", instruction_index, instruction_index, instruction_index)
 			}
 			fmt.sbprintf(&emitter.builder, "  br i1 %%slice_ok%d, label %%slice_continue%d, label %%slice_trap%d\nslice_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
 			message := diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "slice bounds out of range")
 			emit_trap_call(emitter, message)
 			fmt.sbprintf(&emitter.builder, "  unreachable\nslice_continue%d:\n", instruction_index)
+			if check_sentinel {
+				element_type := llvm_type(item.child, &emitter.module.types)
+				fmt.sbprintf(&emitter.builder, "  %%slice_sentinel_ptr%d = getelementptr %s, ptr %s, i64 %s\n", instruction_index, element_type, pointer_name, end_name)
+				fmt.sbprintf(&emitter.builder, "  %%slice_sentinel_value%d = load %s, ptr %%slice_sentinel_ptr%d\n", instruction_index, element_type, instruction_index)
+				fmt.sbprintf(&emitter.builder, "  %%slice_sentinel_ok%d = icmp eq %s %%slice_sentinel_value%d, ", instruction_index, element_type, instruction_index)
+				write_operand(&emitter.builder, instructions, instruction.b, item.child, &emitter.module.types)
+				fmt.sbprintf(&emitter.builder, "\n  br i1 %%slice_sentinel_ok%d, label %%slice_sentinel_continue%d, label %%slice_sentinel_trap%d\nslice_sentinel_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+				sentinel_message := diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "slice sentinel mismatch")
+				emit_trap_call(emitter, sentinel_message)
+				fmt.sbprintf(&emitter.builder, "  unreachable\nslice_sentinel_continue%d:\n", instruction_index)
+			}
 			fmt.sbprintf(&emitter.builder, "  %%slice_start%d = getelementptr %s, ptr %s, i64 %s\n", instruction_index, llvm_type(item.child, &emitter.module.types), pointer_name, start_name)
 			fmt.sbprintf(&emitter.builder, "  %%slice_result%d = insertvalue %s poison, ptr %%slice_start%d, 0\n", instruction_index, llvm_type(instruction.type, &emitter.module.types), instruction_index)
 			fmt.sbprintf(&emitter.builder, "  %%slice_result_len%d = sub i64 %s, %s\n", instruction_index, end_name, start_name)
@@ -2729,6 +2757,11 @@ emit_functions :: proc(emitter: ^Emitter) {
 		if function.implementation == .Declaration && function.link_name == "write" {
 			continue
 		}
+		if emitter.prepares_args && function.implementation == .Declaration &&
+		   (function.link_name == "malloc" || function.link_name == "free" ||
+		    function.link_name == "strlen" || function.link_name == "exit") {
+			continue
+		}
 		if function.implementation == .Declaration {
 			duplicate := false
 			for previous in emitter.module.functions[:function_index] {
@@ -2863,6 +2896,59 @@ emit_declarations :: proc(emitter: ^Emitter) {
 		&emitter.builder,
 		"\ndefine internal void @bro.trap(ptr %message, i64 %length) noreturn {\nentry:\n  %written = call i64 @write(i32 2, ptr %message, i64 %length)\n  call void @llvm.trap()\n  unreachable\n}\n\n",
 	)
+	if emitter.prepares_args {
+		emit_argument_runtime(emitter)
+	}
+}
+
+// Only native entry wrappers own these descriptors; argument bytes stay borrowed.
+emit_argument_runtime :: proc(emitter: ^Emitter) {
+	strings.write_string(&emitter.builder, `declare ptr @malloc(i64)
+declare void @free(ptr)
+declare i64 @strlen(ptr)
+declare void @exit(i32) noreturn
+
+define internal { ptr, i64 } @bro.prepare_args(i32 %argc, ptr %argv) {
+entry:
+  %negative = icmp slt i32 %argc, 0
+  br i1 %negative, label %failure, label %check_empty
+check_empty:
+  %count = zext i32 %argc to i64
+  %empty = icmp eq i64 %count, 0
+  br i1 %empty, label %empty_result, label %check_size
+check_size:
+  %allocation = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %count, i64 16)
+  %size = extractvalue { i64, i1 } %allocation, 0
+  %overflow = extractvalue { i64, i1 } %allocation, 1
+  br i1 %overflow, label %failure, label %allocate
+allocate:
+  %data = call ptr @malloc(i64 %size)
+  %failed = icmp eq ptr %data, null
+  br i1 %failed, label %failure, label %loop
+loop:
+  %index = phi i64 [ 0, %allocate ], [ %next, %loop ]
+  %native = getelementptr ptr, ptr %argv, i64 %index
+  %string = load ptr, ptr %native
+  %length = call i64 @strlen(ptr %string)
+  %descriptor = getelementptr { ptr, i64 }, ptr %data, i64 %index
+  %with_pointer = insertvalue { ptr, i64 } poison, ptr %string, 0
+  %argument = insertvalue { ptr, i64 } %with_pointer, i64 %length, 1
+  store { ptr, i64 } %argument, ptr %descriptor
+  %next = add i64 %index, 1
+  %more = icmp ult i64 %next, %count
+  br i1 %more, label %loop, label %done
+done:
+  %result_pointer = insertvalue { ptr, i64 } poison, ptr %data, 0
+  %result = insertvalue { ptr, i64 } %result_pointer, i64 %count, 1
+  ret { ptr, i64 } %result
+empty_result:
+  ret { ptr, i64 } zeroinitializer
+failure:
+  call void @exit(i32 2)
+  unreachable
+}
+
+`)
 }
 
 emit :: proc(
@@ -2878,6 +2964,14 @@ emit :: proc(
 		builder=strings.builder_make(allocator),
 		allocator=allocator,
 	}
+	for function in module.functions {
+		for instruction in function.instructions {
+			if instruction.op == .Prepare_Args {
+				emitter.prepares_args = true
+				break
+			}
+		}
+	}
 	emitter.messages.allocator = allocator
 	defer {
 		for message in emitter.messages {

compiler/lower/lower.odin

@@ -306,9 +306,13 @@ lower_compound_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instructi
 				args[index] = lower_nested_expr(state, arg)
 			}
 		}
+		checked_sentinel := ir.INVALID_INSTRUCTION
+		if expr.right != hir.INVALID_EXPR {
+			checked_sentinel = lower_nested_expr(state, expr.right)
+		}
 		return append_instruction(state, ir.Instruction{
 			op=.Slice, span=expr.span, type=expr.type, args=args,
-			target=ir.INVALID_REF, a=container, b=ir.INVALID_INSTRUCTION,
+			target=ir.INVALID_REF, a=container, b=checked_sentinel,
 			diagnostic=source.INVALID_DIAGNOSTIC,
 		})
 	case .Unwrap:
@@ -1778,8 +1782,48 @@ append_injected_main :: proc(module: ^ir.Module, hir_module: ^hir.Module, alloca
 
 	instructions: [dynamic]ir.Instruction
 	instructions.allocator = allocator
+	param_types: []types.Type
 	args: []ir.Instruction_Id
+	prepared_args := ir.INVALID_INSTRUCTION
 	if param_index >= 0 {
+		init_type := main_function.locals[param_index].type
+		init_fields := types.fields_for(&module.types, init_type)
+		io_index := 0
+		if !types.equal(
+			types.resolve_alias(init_fields[0].type, &module.types),
+			types.resolve_alias(hir_module.functions[provider_index].result, &module.types),
+		) {
+			io_index = 1
+		}
+		args_index := 1 - io_index
+		args_type := types.resolve_alias(init_fields[args_index].type, &module.types)
+		values_type := types.resolve_alias(types.fields_for(&module.types, args_type)[0].type, &module.types)
+		argument_pointer := types.pointer(&module.types, types.U8, false, true, true, 0)
+		argv_type := types.pointer(&module.types, argument_pointer, false, true)
+		param_types = make([]types.Type, 2, allocator)
+		param_types[0] = types.C_INT
+		param_types[1] = argv_type
+		for param_type, index in param_types {
+			append(&instructions, ir.Instruction{
+				op=.Param, type=param_type, target=ir.local_ref(ir.Local_Id(index)),
+				a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+		}
+		prepared_args = ir.instruction_id(len(instructions))
+		append(&instructions, ir.Instruction{
+			op=.Prepare_Args, type=values_type, target=ir.INVALID_REF,
+			a=ir.Instruction_Id(0), b=ir.Instruction_Id(1),
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
+		values_args := make([]ir.Instruction_Id, 1, allocator)
+		values_args[0] = prepared_args
+		process_args := ir.instruction_id(len(instructions))
+		append(&instructions, ir.Instruction{
+			op=.Aggregate, type=args_type, args=values_args, target=ir.INVALID_REF,
+			a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
 		provider_call := ir.instruction_id(len(instructions))
 		append(&instructions, ir.Instruction{
 			op=.Call,
@@ -1789,12 +1833,13 @@ append_injected_main :: proc(module: ^ir.Module, hir_module: ^hir.Module, alloca
 			b=ir.INVALID_INSTRUCTION,
 			diagnostic=source.INVALID_DIAGNOSTIC,
 		})
-		init_args := make([]ir.Instruction_Id, 1, allocator)
-		init_args[0] = provider_call
+		init_args := make([]ir.Instruction_Id, len(init_fields), allocator)
+		init_args[io_index] = provider_call
+		init_args[args_index] = process_args
 		init_value := ir.instruction_id(len(instructions))
 		append(&instructions, ir.Instruction{
 			op=.Aggregate,
-			type=main_function.locals[param_index].type,
+			type=init_type,
 			args=init_args,
 			target=ir.INVALID_REF,
 			a=ir.INVALID_INSTRUCTION,
@@ -1814,6 +1859,13 @@ append_injected_main :: proc(module: ^ir.Module, hir_module: ^hir.Module, alloca
 		b=ir.INVALID_INSTRUCTION,
 		diagnostic=source.INVALID_DIAGNOSTIC,
 	})
+	if prepared_args != ir.INVALID_INSTRUCTION {
+		append(&instructions, ir.Instruction{
+			op=.Free_Args, type=types.VOID, target=ir.INVALID_REF,
+			a=prepared_args, b=ir.INVALID_INSTRUCTION,
+			diagnostic=source.INVALID_DIAGNOSTIC,
+		})
+	}
 
 	if types.kind(main_function.result, &hir_module.types) == .Fallible {
 		success := types.fallible_success(main_function.result, &hir_module.types)
@@ -1919,6 +1971,7 @@ append_injected_main :: proc(module: ^ir.Module, hir_module: ^hir.Module, alloca
 		implementation=.Definition,
 		linkage=.External,
 		is_main=true,
+		param_types=param_types,
 		result=types.I32,
 		instructions=instructions[:],
 		problematic=problematic,

compiler/parser/parser.odin

@@ -429,7 +429,8 @@ parse_type_atom :: proc(parser: ^Parser) -> ast.Type_Syntax {
 		return types.BOOL
 	case .Left_Paren:
 		advance(parser)
-		grouped := parse_type(parser)
+		skip_newlines(parser)
+		grouped := parse_type_pipe_tail(parser, parse_type_atom(parser), true)
 		if _, ok := allow(parser, .Right_Paren); !ok {
 			source.add(parser.diagnostics, current(parser).span, "expected ')' after grouped type")
 		}
@@ -533,10 +534,19 @@ sum_syntax_requires_resolution :: proc(parser: ^Parser, value: types.Type, depth
 	return false
 }
 
-parse_type_pipe_tail :: proc(parser: ^Parser, left: ast.Type_Syntax) -> ast.Type_Syntax {
+parse_type_pipe_tail :: proc(parser: ^Parser, left: ast.Type_Syntax, multiline := false) -> ast.Type_Syntax {
 	result := left
-	for current(parser).kind == .Pipe {
+	for {
+		if multiline {
+			skip_newlines(parser)
+		}
+		if current(parser).kind != .Pipe {
+			break
+		}
 		operator := advance(parser)
+		if multiline {
+			skip_newlines(parser)
+		}
 		right := parse_type_atom(parser)
 		composed, compose_error := types.compose_sum(&parser.module.type_store, result, right)
 		if compose_error == .Unsupported {
@@ -1440,6 +1450,7 @@ parse_expression_bp :: proc(parser: ^Parser, minimum_binding_power, nesting: int
 			skip_newlines(parser)
 			start_expr := ast.INVALID_EXPR
 			end_expr := ast.INVALID_EXPR
+			sentinel_expr := ast.INVALID_EXPR
 			slicing := false
 			if _, ok := allow(parser, .Range); ok {
 				slicing = true
@@ -1453,12 +1464,19 @@ parse_expression_bp :: proc(parser: ^Parser, minimum_binding_power, nesting: int
 				}
 			}
 			skip_newlines(parser)
-			if slicing && current(parser).kind != .Right_Bracket {
+			if slicing && current(parser).kind != .Right_Bracket && current(parser).kind != .Semicolon {
 				parser.range_disabled += 1
 				end_expr = parse_expression_bp(parser, 0, nesting+1)
 				parser.range_disabled -= 1
 				skip_newlines(parser)
 			}
+			if slicing {
+				if _, ok := allow(parser, .Semicolon); ok {
+					skip_newlines(parser)
+					sentinel_expr = parse_expression_bp(parser, 0, nesting+1)
+					skip_newlines(parser)
+				}
+			}
 			end_token, ok := allow(parser, .Right_Bracket)
 			if !ok {
 				source.add(parser.diagnostics, current(parser).span, "expected ']' after index or slice")
@@ -1475,7 +1493,7 @@ parse_expression_bp :: proc(parser: ^Parser, minimum_binding_power, nesting: int
 					span=span_from(left_expr.span, end_token.span),
 					args=args,
 					left=left,
-					right=ast.INVALID_EXPR,
+					right=sentinel_expr,
 					diagnostic=source.INVALID_DIAGNOSTIC,
 				})
 			} else {

compiler_tests.odin

@@ -2252,6 +2252,256 @@ main func() i32 {
 	testing.expect(t, strings.contains(llvm_text, "getelementptr [4 x i32], ptr"))
 }
 
+@(test)
+explicit_sentinel_slices_execute_without_copying :: proc(t: ^testing.T) {
+	directory := "/tmp/brolang-test-explicit-sentinel-slices"
+	main_path := "/tmp/brolang-test-explicit-sentinel-slices/main.bro"
+	output := "/tmp/brolang-test-explicit-sentinel-slices-output"
+	text := `pointer func(value *mut u8, count usize) [;0]mut u8 { return value[..count;0] }
+bounded func(value []u8, count usize) [;0]u8 { return value[..count;0] }
+array func(value @mut [3]mut u8, start usize, count usize) [;0]mut u8 { return value[start..count;0] }
+terminated func(value [;0]u8) [;0]u8 { return value[..;0] }
+nonzero func(value [*;9]u8, count usize) [;9]u8 { return value[1..count;9] }
+signed func(value *i16, count usize) [;-7]i16 { return value[..count;-7] }
+argument func(value [*;0]u8, present bool) ?[;0]u8 {
+	if !present { return null }
+	length usize := 0
+	while value[length] != 0 { length += 1 }
+	return value[..length;0]
+}
+static_text func() [;0]u8 { return "hello"[..;0] }
+static_partial func() [;7]u16 {
+	values [4]u16 := [11, 22, 7, 44]
+	return values[1..2;7]
+}
+comptime_text [;0]u8 :: $static_text()
+comptime_partial [;7]u16 :: $static_partial()
+equal func($T type, left, right []T) bool {
+	if left.len != right.len { return false }
+	for 0..left.len |index| {
+		if left[index] != right[index] { return false }
+	}
+	return true
+}
+main func() i32 {
+	values [3]mut u8 := [11, 22, 0]
+	view :: pointer((&values).ptr, 2)
+	if view.len != 2 { return 1 }
+	view[0] = 33
+	if values[0] != 33 { return 2 }
+	all :: values[..]
+	if all.len != 3 { return 3 }
+	part :: bounded(all, 2)
+	if part.len != 2 or part[1] != 22 { return 4 }
+	suffix :: array(&values, 1, 2)
+	suffix[0] = 44
+	if suffix.len != 1 or values[1] != 44 { return 5 }
+	empty :: pointer((&values).ptr + 2, 0)
+	if empty.len != 0 { return 6 }
+	zeros [2;0]mut u8 := [1, 2]
+	full :: terminated(zeros[..])
+	if full.len != 2 or full[1] != 2 { return 7 }
+	nines [2;9]u8 := [3, 4]
+	nine :: nonzero((&nines).ptr, 2)
+	if nine.len != 1 or nine[0] != 4 { return 8 }
+	wide [2]i16 := [123, -7]
+	negative :: signed((&wide).ptr, 1)
+	if negative.len != 1 or negative[0] != 123 { return 9 }
+	direct :: zeros[..;0]
+	if direct.len != 2 { return 10 }
+	if argument((&zeros).ptr, true) |arg| {
+		zeros[0] = 55
+		if arg.len != 2 or arg[0] != 55 { return 11 }
+	} else { return 12 }
+	if argument((&zeros).ptr, false) |_| { return 13 }
+	if comptime_text.len != 5 or comptime_text[0] != 'h' or comptime_text[4] != 'o' { return 14 }
+	if comptime_partial.len != 1 or comptime_partial[0] != 22 { return 15 }
+	if !equal(comptime_text, "hello") or equal(comptime_text, "hellx") { return 16 }
+	if !equal(direct, "7\x02") { return 17 }
+	return 0
+}
+`
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	defer _ = os.remove(output)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)text))
+	testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
+@(test)
+explicit_sentinel_slice_runtime_guards_trap :: proc(t: ^testing.T) {
+	cases := [?]struct {
+		text, message: string,
+	}{
+		{
+			`check func(value *u8, count usize) void { _ = value[..count;0] }
+main func() void {
+	values [2]u8 := [1, 2]
+	check((&values).ptr, 1)
+}
+`, "slice sentinel mismatch",
+		},
+		{
+			`check func(value @[2]u8, count usize) void { _ = value[..count;0] }
+main func() void {
+	values [2]u8 := [1, 0]
+	check(&values, 2)
+}
+`, "slice bounds out of range",
+		},
+		{
+			`check func(value []u8, count usize) void { _ = value[..count;0] }
+main func() void {
+	values [2;0]u8 := [1, 2]
+	check(values[..2], 2)
+}
+`, "slice bounds out of range",
+		},
+		{
+			`check func(value [;0]u8, count usize) void { _ = value[..count;0] }
+main func() void {
+	values [2;0]u8 := [1, 2]
+	check(values[..], 3)
+}
+`, "slice bounds out of range",
+		},
+		{
+			`check func(value *u8, start usize, count usize) void { _ = value[start..count;0] }
+main func() void {
+	values [2]u8 := [1, 0]
+	check((&values).ptr, 2, 1)
+}
+`, "slice bounds out of range",
+		},
+		{
+			`check func(value [;0]u8, count usize) void { _ = value[..count;9] }
+main func() void {
+	values [2;0]u8 := [1, 2]
+	check(values[..], 2)
+}
+`, "slice sentinel mismatch",
+		},
+	}
+	for test_case, index in cases {
+		directory := fmt.tprintf("/tmp/brolang-test-sentinel-slice-trap-%d", index)
+		main_path := fmt.tprintf("%s/main.bro", directory)
+		output := fmt.tprintf("%s-output", directory)
+		_ = os2.remove_all(directory)
+		defer _ = os2.remove_all(directory)
+		defer _ = os.remove(output)
+		testing.expect(t, os.make_directory(directory) == nil)
+		testing.expect(t, os.write_entire_file(main_path, transmute([]byte)test_case.text))
+		testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
+		state, stdout, stderr, err := os2.process_exec(
+			os2.Process_Desc{command=[]string{output}}, context.allocator,
+		)
+		defer delete(stdout)
+		defer delete(stderr)
+		testing.expect(t, err == nil)
+		testing.expect(t, !state.success)
+		testing.expect(t, strings.contains(string(stderr), test_case.message))
+	}
+}
+
+@(test)
+explicit_sentinel_slice_semantic_errors_are_diagnosed :: proc(t: ^testing.T) {
+	cases := [?]struct {
+		text, message: string,
+	}{
+		{
+			`bad func(value *u8, count usize, mark u8) void { _ = value[..count;mark] }
+main func() void {
+	values [2]u8 := [1, 0]
+	bad((&values).ptr, 1, 0)
+}
+`, "slice sentinel must be a compile-time integer",
+		},
+		{
+			`bad func(value *u8, count usize) void { _ = value[..count;true] }
+main func() void {
+	values [2]u8 := [1, 0]
+	bad((&values).ptr, 1)
+}
+`, "slice sentinel must be a compile-time integer",
+		},
+		{
+			`bad func(value *u8, count usize) void { _ = value[..count;256] }
+main func() void {
+	values [2]u8 := [1, 0]
+	bad((&values).ptr, 1)
+}
+`, "slice sentinel value does not fit element type",
+		},
+		{
+			`bad func(value *u8, count usize) void { _ = value[..count;-1] }
+main func() void {
+	values [2]u8 := [1, 0]
+	bad((&values).ptr, 1)
+}
+`, "slice sentinel value does not fit element type",
+		},
+		{
+			`bad func(value [*;0]u8) void { _ = value[..;0] }
+main func() void { bad("text") }
+`, "many-item pointer slicing requires an explicit end bound",
+		},
+		{
+			`bad func(value *u8, count usize) [;0]mut u8 { return value[..count;0] }
+main func() void {
+	values [2]u8 := [1, 0]
+	_ = bad((&values).ptr, 1)
+}
+`, "cannot implicitly convert",
+		},
+		{
+			`bad func(count usize) usize {
+	values [2]u8 := [1, 0]
+	return values[..count;0].len
+}
+result :: $bad(2)
+main func() void { _ = result }
+`, "comptime sentinel slice endpoint out of range",
+		},
+		{
+			`bad func(count usize) usize {
+	values [2]u8 := [1, 2]
+	return values[..count;0].len
+}
+result :: $bad(1)
+main func() void { _ = result }
+`, "comptime slice sentinel mismatch",
+		},
+		{
+			`bad func(value []u8) usize { return value[..;0].len }
+result :: $bad("text")
+main func() void { _ = result }
+`, "comptime sentinel slice endpoint out of range",
+		},
+	}
+	for test_case in cases {
+		source_file := source.Source{path="invalid_sentinel_slice.bro", text=test_case.text}
+		diagnostics := source.init_diagnostics(&source_file)
+		defer source.destroy_diagnostics(&diagnostics)
+		symbols := symbol.init_table()
+		defer symbol.destroy_table(&symbols)
+		stream := lexer.lex(&source_file, &diagnostics, &symbols)
+		defer delete(stream.items)
+		ast_module := parser.parse(&stream, &source_file, &diagnostics)
+		defer ast.destroy_module(&ast_module)
+		hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+		defer hir.destroy_module(&hir_module)
+
+		found := false
+		for diagnostic in diagnostics.items {
+			found = found || strings.contains(diagnostic.message, test_case.message)
+		}
+		testing.expect(t, found, test_case.message)
+	}
+}
+
 @(test)
 slicing_an_array_rvalue_materializes_a_temporary :: proc(t: ^testing.T) {
 	// The checker accepts slicing a non-location array (here, a by-value array
@@ -3284,10 +3534,28 @@ main func() int ! Error { return try value() }
 			source=`process :: import "@std/process"
 Error :: enum { failed }
 fail func() void ! Error { return .failed }
-main func(_ process.Init) void ! Error { try fail() }
+main func(init process.Init) void ! Error {
+	if init.args.values.len != 3 { return }
+	if init.args.values[1].len != 0 or init.args.values[2].len != 9 { return }
+	if init.args.values[2][0] != 't' or init.args.values[2][8] != 's' { return }
+	try fail()
+}
 `,
 			exit_code=1,
 		},
+		{
+			name="process-success",
+			source=`process :: import "@std/process"
+Error :: enum { failed }
+main func(init process.Init) i32 ! Error {
+	if init.args.values.len != 3 { return .failed }
+	if init.args.values[1].len != 0 or init.args.values[2].len != 9 { return .failed }
+	if init.args.values[2][0] != 't' or init.args.values[2][8] != 's' { return .failed }
+	return 7
+}
+`,
+			exit_code=7,
+		},
 		{
 			name="inferred-main-try",
 			source=`Error :: enum { failed }
@@ -3328,7 +3596,12 @@ main func() void! { try dispatch(2) }
 			source=`process :: import "@std/process"
 Error :: enum { failed }
 fail func() void ! Error { return .failed }
-main func(_ process.Init) void! { try fail() }
+main func(init process.Init) void! {
+	if init.args.values.len != 3 { return }
+	if init.args.values[1].len != 0 or init.args.values[2].len != 9 { return }
+	if init.args.values[2][0] != 't' or init.args.values[2][8] != 's' { return }
+	try fail()
+}
 `,
 			exit_code=1,
 		},
@@ -3353,7 +3626,7 @@ main func(_ process.Init) void! { try fail() }
 		)
 		testing.expect_value(t, status, 0)
 		state, stdout, stderr, _ := os2.process_exec(
-			os2.Process_Desc{command=[]string{output}},
+			os2.Process_Desc{command=[]string{output, "", "two words"}},
 			context.allocator,
 		)
 		defer delete(stdout)
@@ -3468,7 +3741,6 @@ milestone_33_injects_explicit_io_provider_and_runs_std_io :: proc(t: ^testing.T)
 	testing.expect_value(t, len(diagnostics.items), 0)
 	testing.expect(t, hir_module.injected_main != hir.INVALID_FUNCTION)
 	testing.expect(t, hir_module.io_provider != hir.INVALID_FUNCTION)
-	testing.expect_value(t, count_substring_occurrences(llvm_text, "define i32 @main()"), 1)
 	testing.expect_value(t, count_substring_occurrences(llvm_text, "define internal fastcc i32 @bro__p0__main__"), 1)
 	testing.expect_value(t, count_substring_occurrences(llvm_text, "declare i64 @write("), 1)
 
@@ -3685,7 +3957,6 @@ milestone_37_validates_process_init_and_hidden_system_provider :: proc(t: ^testi
 	Case :: struct {
 		io_source: string,
 		process_source: string,
-		message: string,
 	}
 	cases := []Case{
 		{
@@ -3693,18 +3964,54 @@ milestone_37_validates_process_init_and_hidden_system_provider :: proc(t: ^testi
 system func() Io { return Io {value = 0} }
 `,
 			process_source=`io :: import "@std/io"
-Init :: struct { io io.Io }
+Args :: struct { values [][;0]u8 }
+Init :: struct { io io.Io, args Args }
 `,
-			message="does not provide the required '@hide system func() Io'",
 		},
 		{
 			io_source=`Io :: struct { value i32 }
 @hide system func() Io { return Io {value = 0} }
 `,
 			process_source=`io :: import "@std/io"
-Init :: struct { io io.Io, extra i32 }
+Args :: struct { values [][;0]u8 }
+Init :: struct { io io.Io, args Args, extra i32 }
+`,
+		},
+		{
+			io_source=`Io :: struct { value i32 }
+@hide system func() Io { return Io {value = 0} }
+`,
+			process_source=`io :: import "@std/io"
+Args :: struct { values [][;0]u8 }
+Init :: struct { io io.Io }
+`,
+		},
+		{
+			io_source=`Io :: struct { value i32 }
+@hide system func() Io { return Io {value = 0} }
+`,
+			process_source=`io :: import "@std/io"
+Args :: struct { values [][]u8 }
+Init :: struct { io io.Io, args Args }
+`,
+		},
+		{
+			io_source=`Io :: struct { value i32 }
+@hide system func() Io { return Io {value = 0} }
+`,
+			process_source=`io :: import "@std/io"
+Args :: struct { values [][;0]u8, extra i32 }
+Init :: struct { io io.Io, args Args }
+`,
+		},
+		{
+			io_source=`Io :: struct { value i32 }
+@hide system func() Io { return Io {value = 0} }
+`,
+			process_source=`io :: import "@std/io"
+Args :: struct { values [][;0]u8 }
+Init :: struct { io io.Io, args i32 }
 `,
-			message="Init must be an auto-layout record containing exactly 'io io.Io'",
 		},
 	}
 	for test_case, index in cases {
@@ -3735,12 +4042,8 @@ main func(init process.Init) void { _ = init }
 		symbols := symbol.init_table()
 		ast_module, loaded := loader.load(app, &sources, &diagnostics, &symbols, project_root_path=root)
 		hir_module := checker.check(&ast_module, &diagnostics, &symbols)
-		found := false
-		for diagnostic in diagnostics.items {
-			found = found || strings.contains(diagnostic.message, test_case.message)
-		}
 		testing.expect(t, loaded)
-		testing.expect(t, found)
+		testing.expect(t, len(diagnostics.items) > 0)
 		hir.destroy_module(&hir_module)
 		ast.destroy_module(&ast_module)
 		symbol.destroy_table(&symbols)
@@ -3749,6 +4052,131 @@ main func(init process.Init) void { _ = init }
 	}
 }
 
+@(test)
+process_init_supplies_native_argument_slices :: proc(t: ^testing.T) {
+	directory := "/tmp/brolang-test-process-args"
+	main_path := "/tmp/brolang-test-process-args/main.bro"
+	output := "/tmp/brolang-test-process-args/app"
+	text := `process :: import "@std/process"
+io :: import "@std/io"
+mem :: import "@std/mem"
+
+main func(init process.Init) i32 {
+	count :: init.args.values.len
+	if count != 1 and count != 4 and count != 16385 { return 1 }
+	if !mem.eql(init.args.values[0], "/tmp/brolang-test-process-args/app") { return 2 }
+	if count == 4 {
+		if !mem.eql(init.args.values[1], "run") { return 3 }
+		if init.args.values[2].len != 0 { return 4 }
+		if !mem.eql(init.args.values[3], "two words") { return 5 }
+	}
+	if count == 16385 {
+		index := usize(1)
+		while index < count {
+			if init.args.values[index].len != 0 { return 6 }
+			index += 1
+		}
+	}
+	io.write_all(io.stdout(init.io), "args-ok\n") catch |_| { return 7 }
+	return 0
+}
+`
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)text))
+	testing.expect_value(t, compiler_core.compile_package(
+		directory, output, nil, target.DEFAULT, cimport.Options{}, ".",
+	), 0)
+	large_command := make([]string, 16385)
+	defer delete(large_command)
+	large_command[0] = output
+	for index in 1..<len(large_command) {
+		large_command[index] = ""
+	}
+	commands := [][]string{
+		{output},
+		{output, "run", "", "two words"},
+		large_command,
+	}
+	for command in commands {
+		state, stdout, stderr, error := os2.process_exec(
+			os2.Process_Desc{command=command}, context.allocator,
+		)
+		testing.expect(t, error == nil)
+		testing.expect_value(t, state.exit_code, 0)
+		testing.expect_value(t, string(stdout), "args-ok\n")
+		testing.expect_value(t, len(stderr), 0)
+		delete(stdout)
+		delete(stderr)
+	}
+
+	plain_main := "main func() i32 { return 37 }\n"
+	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)plain_main))
+	testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
+	for command in commands {
+		state, stdout, stderr, error := os2.process_exec(
+			os2.Process_Desc{command=command}, context.allocator,
+		)
+		testing.expect(t, error == nil)
+		testing.expect_value(t, state.exit_code, 37)
+		testing.expect_value(t, len(stdout), 0)
+		testing.expect_value(t, len(stderr), 0)
+		delete(stdout)
+		delete(stderr)
+	}
+}
+
+@(test)
+process_init_startup_respects_reordered_fields :: proc(t: ^testing.T) {
+	root := "/tmp/brolang-test-process-reordered"
+	app := "/tmp/brolang-test-process-reordered/app"
+	output := "/tmp/brolang-test-process-reordered/program"
+	io_source := `Io :: struct { value i32 }
+@hide system func() Io { return Io {value = 37} }
+`
+	process_source := `io :: import "@std/io"
+Args :: struct { values [][;0]u8 }
+Init :: struct { args Args, io io.Io }
+`
+	main_source := `process :: import "@std/process"
+main func(init process.Init) i32 {
+	if init.io.value != 37 or init.args.values.len != 3 { return 1 }
+	empty :: init.args.values[1]
+	if empty.len != 0 { return 2 }
+	spaced :: init.args.values[2]
+	if spaced.len != 3 or spaced[0] != 'a' or spaced[1] != ' ' or spaced[2] != 'b' { return 3 }
+	return 0
+}
+`
+	_ = os2.remove_all(root)
+	defer _ = os2.remove_all(root)
+	testing.expect(t, os2.make_directory_all(app) == nil)
+	testing.expect(t, os2.make_directory_all(fmt.tprintf("%s/std/io", root)) == nil)
+	testing.expect(t, os2.make_directory_all(fmt.tprintf("%s/std/process", root)) == nil)
+	testing.expect(t, os.write_entire_file(
+		fmt.tprintf("%s/main.bro", app), transmute([]byte)main_source,
+	))
+	testing.expect(t, os.write_entire_file(
+		fmt.tprintf("%s/std/io/io.bro", root), transmute([]byte)io_source,
+	))
+	testing.expect(t, os.write_entire_file(
+		fmt.tprintf("%s/std/process/process.bro", root), transmute([]byte)process_source,
+	))
+	testing.expect_value(t, compiler_core.compile_package(
+		app, output, nil, target.DEFAULT, cimport.Options{}, root,
+	), 0)
+	state, stdout, stderr, error := os2.process_exec(
+		os2.Process_Desc{command=[]string{output, "", "a b"}}, context.allocator,
+	)
+	defer delete(stdout)
+	defer delete(stderr)
+	testing.expect(t, error == nil)
+	testing.expect_value(t, state.exit_code, 0)
+	testing.expect_value(t, len(stdout), 0)
+	testing.expect_value(t, len(stderr), 0)
+}
+
 @(test)
 milestone_37_tuples_reflection_expand_for_and_debug_print_compile_and_run :: proc(t: ^testing.T) {
 	sources := source.init_store()
@@ -5848,16 +6276,6 @@ main func() void {
 		values [2]mut i32 := [1, 2]
 		yield &values[0]
 	}
-	_ = ${
-		values [2]mut i32 := [1, 2]
-		view []mut i32 := values[..]
-		yield view
-	}
-	_ = ${
-		values [2]mut i32 := [1, 2]
-		view []i32 := values[1..]
-		yield view
-	}
 	_ = $spin()
 	_ = $missing()
 	_ = ${
@@ -5880,7 +6298,6 @@ main func() void {
 	found_runtime := false
 	runtime_only_count := 0
 	pointer_errors := 0
-	slice_errors := 0
 	found_quota := false
 	found_missing := false
 	found_yield := false
@@ -5889,7 +6306,6 @@ main func() void {
 		found_runtime = found_runtime || strings.contains(message, "unresolved comptime value 'runtime'")
 		runtime_only_count += 1 if strings.contains(message, "runtime-only") else 0
 		pointer_errors += 1 if strings.contains(message, "only immutable pointers to whole comptime arrays can materialize as runtime memory") else 0
-		slice_errors += 1 if strings.contains(message, "only immutable full-array comptime slices can materialize as runtime memory") else 0
 		found_quota = found_quota || strings.contains(message, "comptime evaluation exceeded the step quota")
 		found_missing = found_missing || strings.contains(message, "did not return a value")
 		found_yield = found_yield || strings.contains(message, "a value block must end with an explicit 'yield'")
@@ -5897,7 +6313,6 @@ main func() void {
 	testing.expect(t, found_runtime)
 	testing.expect(t, runtime_only_count >= 2)
 	testing.expect(t, pointer_errors >= 4)
-	testing.expect(t, slice_errors >= 2)
 	testing.expect(t, found_quota)
 	testing.expect(t, found_missing)
 	testing.expect(t, found_yield)
@@ -7680,6 +8095,65 @@ main func() i32 {
 	testing.expect(t, strings.contains(llvm_text, "call void @llvm.memcpy.p0.p0.i64"))
 }
 
+@(test)
+multiline_grouped_sum_types_compile_and_run :: proc(t: ^testing.T) {
+	directory :: "/tmp/brolang-test-multiline-sums"
+	output := "/tmp/brolang-test-multiline-sums-output"
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	defer _ = os.remove(output)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.make_directory(directory + "/errors") == nil)
+	errors_text := `AllocError :: enum { alloc }
+CapacityError :: enum { capacity }
+SourceError :: union(enum) { source i32 }
+`
+	testing.expect(t, os.write_entire_file(directory + "/errors/errors.hon", transmute([]byte)errors_text))
+	text := `errors :: import "errors"
+@hide:file
+DriverError :: alias (
+	errors.AllocError
+	| (
+		errors.CapacityError |
+		errors.SourceError
+	)
+)
+code func(err DriverError) i32 {
+	return match err {
+		.alloc: 1
+		.capacity: 2
+		.source |value|: value
+	}
+}
+fail func() void ! (
+	errors.AllocError
+	|
+	errors.CapacityError
+) {
+	return .capacity
+}
+main func() i32 {
+	if (code(.alloc) != 1) return 1
+	if (code(.capacity) != 2) return 2
+	if (code(.source{42}) != 42) return 3
+	result := 0
+	fail() catch |err| {
+		result = code(err)
+	}
+	if (result != 2) return 4
+	return 0
+}
+`
+	testing.expect(t, os.write_entire_file(directory + "/main.hon", transmute([]byte)text))
+	status := compiler_core.compile_package(directory, output)
+	testing.expect_value(t, status, 0)
+	if status != 0 {
+		return
+	}
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
 @(test)
 anonymous_struct_payloads_and_keyed_payload_sugar_compile :: proc(t: ^testing.T) {
 	text := `PayloadError :: union(enum) {

std/process/process.hon

@@ -2,4 +2,9 @@ import "@std/io"
 
 Init :: struct {
 	io io.Io
+	args Args
+}
+
+Args :: struct {
+	values [][;0]u8
 }