labeled block statements

TODO.md

@@ -391,9 +391,16 @@
     loop, a labeled one searches by label). The checker tracks a `loop_labels` stack and a
     `Yield_Target.defer_floor`; a `yield :L v` desugars to `slot = v; flush defers to L's body;
     break :L`, reusing the milestone-18 break lowering — **no new IR opcode, no emitter change**
-  - deferred (`// ponytail:`): a labeled bare block as a *plain statement* with `break :blk`;
-    `none`-before-concrete typing in an untyped block whose first concrete yield references a
-    block local (annotate instead)
+  - a labeled bare block as a *plain statement* is also exitable with `break :blk` (a HIR
+    `.Block` break target; not a loop, so unlabeled `break`/`continue` and `continue :blk` skip
+    it). The checker tracks a parallel `loop_is_loop` stack so labeled `break` reaches a loop or
+    block while `continue` and unlabeled `break`/`continue` reach only the innermost loop
+  - untyped block `none`-before-concrete typing now builds the block's leading (yield-free)
+    statements first (a throwaway probe), so a first concrete `yield :blk` that references a
+    block local still resolves the result to `?T`
+  - deferred (`// ponytail:`): the same `none`-before-concrete typing in an untyped block (or
+    loop) whose concrete yield references a local declared *past* the first yield (annotate);
+    same-label loop/block shadowing resolves innermost-wins
 
 21. unions and tagged unions
 

compiler/checker/checker.odin

@@ -95,9 +95,12 @@ Build_Ctx :: struct {
 	// only see loops opened within the defer (those past `loop_floor`).
 	defers:            ^[dynamic][]hir.Stmt_Id,
 	loop_defer_starts: ^[dynamic]int,
-	// Parallel to `loop_defer_starts`: the label of each enclosing loop (INVALID when
-	// unlabeled), so a `break :L` / `continue :L` can target an outer labeled loop.
+	// Parallel to `loop_defer_starts`: the label of each enclosing break target (INVALID
+	// when unlabeled), so a `break :L` / `continue :L` can target an outer one. A labeled
+	// block statement is a break target too; `loop_is_loop` distinguishes loops (which
+	// `continue` and unlabeled `break`/`continue` target) from value/labeled blocks.
 	loop_labels:       ^[dynamic]symbol.Id,
+	loop_is_loop:      ^[dynamic]bool,
 	defer_depth:       int,
 	loop_floor:        int,
 }
@@ -4603,7 +4606,9 @@ build_block :: proc(
 			}
 			append(ctx.loop_defer_starts, len(ctx.defers^))
 			append(ctx.loop_labels, statement.label)
+			append(ctx.loop_is_loop, true)
 			loop_body := build_block(ctx, statement.body)
+			pop(ctx.loop_is_loop)
 			pop(ctx.loop_labels)
 			pop(ctx.loop_defer_starts)
 			update := hir.INVALID_STMT
@@ -4700,7 +4705,9 @@ build_block :: proc(
 			}
 			append(ctx.loop_defer_starts, len(ctx.defers^))
 			append(ctx.loop_labels, statement.label)
+			append(ctx.loop_is_loop, true)
 			loop_body := build_block(ctx, statement.body, capture_start)
+			pop(ctx.loop_is_loop)
 			pop(ctx.loop_labels)
 			pop(ctx.loop_defer_starts)
 			resize(ctx.locals, capture_start)
@@ -4740,14 +4747,22 @@ build_block :: proc(
 			// hides the loops opened outside the defer.
 			target_index := -1
 			if symbol.is_valid(statement.label) {
+				// `break :L` targets a labeled loop or block; `continue :L` only a loop.
 				for i := len(ctx.loop_labels^) - 1; i >= ctx.loop_floor; i -= 1 {
-					if ctx.loop_labels^[i] == statement.label {
+					if ctx.loop_labels^[i] == statement.label &&
+					   (ctx.loop_is_loop^[i] || statement.kind == .Break) {
+						target_index = i
+						break
+					}
+				}
+			} else {
+				// Unlabeled `break`/`continue` targets the innermost loop, skipping blocks.
+				for i := len(ctx.loop_defer_starts^) - 1; i >= ctx.loop_floor; i -= 1 {
+					if ctx.loop_is_loop^[i] {
 						target_index = i
 						break
 					}
 				}
-			} else if len(ctx.loop_defer_starts^) > ctx.loop_floor {
-				target_index = len(ctx.loop_defer_starts^) - 1
 			}
 			if target_index < 0 {
 				keyword := "break" if statement.kind == .Break else "continue"
@@ -4776,6 +4791,25 @@ build_block :: proc(
 				local = hir.INVALID_LOCAL, diagnostic = source.INVALID_DIAGNOSTIC,
 			})
 		case .Block:
+			if symbol.is_valid(statement.label) {
+				// A labeled block statement (`blk: { … break :blk … }`): a break target
+				// with an exit-label boundary, built as a HIR `.Block`. Not a loop, so
+				// unlabeled `break`/`continue` and `continue :blk` skip it.
+				append(ctx.loop_defer_starts, len(ctx.defers^))
+				append(ctx.loop_labels, statement.label)
+				append(ctx.loop_is_loop, false)
+				built := build_block(ctx, statement.body)
+				pop(ctx.loop_is_loop)
+				pop(ctx.loop_labels)
+				pop(ctx.loop_defer_starts)
+				append(&body, hir.stmt_id(len(checker.module.statements)))
+				append(&checker.module.statements, hir.Stmt{
+					kind = .Block, span = statement.span, label = statement.label,
+					then_body = built, local = hir.INVALID_LOCAL, target = hir.INVALID_EXPR,
+					diagnostic = source.INVALID_DIAGNOSTIC,
+				})
+				continue
+			}
 			// A bare `{ ... }` scope: build it (its own locals/defers are scoped by
 			// the recursive call) and splice its statements in.
 			block := build_block(ctx, statement.body)
@@ -5364,6 +5398,62 @@ value_loop_element_type :: proc(ctx: ^Build_Ctx, loop_stmt: ast.Stmt) -> types.T
 	return result
 }
 
+// stmt_contains_yield reports whether a statement contains a `yield` anywhere within it
+// (recursing through if/block/loop bodies). Used to stop the leading probe build before any
+// statement that yields (the block's yield target is not pushed during the probe).
+stmt_contains_yield :: proc(checker: ^Checker, id: ast.Stmt_Id) -> bool {
+	s := checker.ast_module.statements[id]
+	#partial switch s.kind {
+	case .Yield:
+		return true
+	case .If, .For, .While, .Block:
+		for sub in s.body {
+			if stmt_contains_yield(checker, sub) {
+				return true
+			}
+		}
+		for sub in s.else_body {
+			if stmt_contains_yield(checker, sub) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// block_element_type pre-types an untyped value block's element from its first concrete
+// `yield :blk`, building the block's leading (yield-free) statements first so the probe can
+// reference block locals declared before the first yield. The leading build is a throwaway
+// (its scope is restored). INVALID when there is no concrete yield, or the concrete yield
+// references a local only in scope past the first yield (annotate the binding instead).
+block_element_type :: proc(ctx: ^Build_Ctx, block_stmts: []ast.Stmt_Id) -> types.Type {
+	checker := ctx.checker
+	concrete := first_concrete_yield_expr(checker, block_stmts)
+	if concrete == ast.INVALID_EXPR {
+		return types.INVALID
+	}
+	lead_end := len(block_stmts)
+	for id, i in block_stmts {
+		if stmt_contains_yield(checker, id) {
+			lead_end = i
+			break
+		}
+	}
+	scope_start := len(ctx.locals^)
+	defer_start := len(ctx.defers^)
+	lead := build_block(ctx, block_stmts[:lead_end], close = false)
+	delete(lead, checker.allocator)
+	probe := build_expr(checker, concrete, ctx.locals^[:], ctx.global_reads, ctx.calls, types.INVALID, ctx.pkg, ctx.file)
+	result := checker.module.exprs[probe].type if checker.module.exprs[probe].kind != .Invalid else types.INVALID
+	// Discard the throwaway leading build's scope (its hir stmts/locals are dead but stable).
+	for i := defer_start; i < len(ctx.defers^); i += 1 {
+		delete(ctx.defers^[i], checker.allocator)
+	}
+	resize(ctx.defers, defer_start)
+	resize(ctx.locals, scope_start)
+	return result
+}
+
 // build_value_labeled_block turns `x :: blk: { …; yield :blk v }` into a result slot each
 // `yield :blk` assigns (via the build_block `.Yield` desugar → `slot = v; break :blk`), then
 // reads it after the block. Every path must yield (or otherwise exit); HIR holds a `.Block`
@@ -5388,14 +5478,12 @@ build_value_labeled_block :: proc(
 		result_optional = types.is_optional(slot_type, &checker.module.types)
 	} else if result_optional {
 		// Untyped block that also yields `none`: pre-type the element from the first
-		// concrete yield (a block has no captures, so a capture-free probe suffices).
-		elem := first_concrete_yield_expr(checker, block_stmts)
-		if elem != ast.INVALID_EXPR {
-			probe := build_expr(checker, elem, ctx.locals^[:], ctx.global_reads, ctx.calls, types.INVALID, ctx.pkg, ctx.file)
-			if checker.module.exprs[probe].kind != .Invalid {
-				slot_type = types.optional(&checker.module.types, checker.module.exprs[probe].type)
-				slot = new_value_slot(ctx, slot_type)
-			}
+		// concrete yield (regardless of source order) so a `none` yielded first still
+		// resolves the result to `?T`.
+		elem := block_element_type(ctx, block_stmts)
+		if is_runtime_type(checker, elem) {
+			slot_type = types.optional(&checker.module.types, elem)
+			slot = new_value_slot(ctx, slot_type)
 		}
 	}
 	append(ctx.yield_targets, Yield_Target{
@@ -5722,6 +5810,8 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 	loop_defer_starts.allocator = checker.allocator
 	loop_labels: [dynamic]symbol.Id
 	loop_labels.allocator = checker.allocator
+	loop_is_loop: [dynamic]bool
+	loop_is_loop.allocator = checker.allocator
 	yield_targets: [dynamic]Yield_Target
 	yield_targets.allocator = checker.allocator
 	ctx := Build_Ctx{
@@ -5738,6 +5828,7 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 		defers = &defers,
 		loop_defer_starts = &loop_defer_starts,
 		loop_labels = &loop_labels,
+		loop_is_loop = &loop_is_loop,
 		yield_targets = &yield_targets,
 	}
 	block := build_block(&ctx, function.body)
@@ -5789,6 +5880,7 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 	delete(defers)
 	delete(loop_defer_starts)
 	delete(loop_labels)
+	delete(loop_is_loop)
 	delete(yield_targets)
 	delete(locals)
 }

compiler/parser/parser.odin

@@ -1058,14 +1058,16 @@ parse_loop_control :: proc(parser: ^Parser, kind: ast.Stmt_Kind) -> ast.Stmt_Id
 }
 
 // A bare `{ ... }` introduces a nested scope. Locals declared inside are not
-// visible after it, and any `defer`s inside it run at the closing brace.
-parse_block_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
+// visible after it, and any `defer`s inside it run at the closing brace. A labeled
+// `blk: { ... }` can be exited early with `break :blk`.
+parse_block_statement :: proc(parser: ^Parser, label := symbol.INVALID) -> ast.Stmt_Id {
 	start := current(parser).span // the '{'
 	body := parse_block(parser)
 	id := ast.stmt_id(len(parser.module.statements))
 	append(&parser.module.statements, ast.Stmt{
 		kind=.Block,
 		span=start,
+		label=label,
 		body=body,
 		expr=ast.INVALID_EXPR,
 		update=ast.INVALID_STMT,
@@ -1159,6 +1161,12 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	if current(parser).kind == .Left_Brace {
 		return parse_block_statement(parser)
 	}
+	// `blk: { ... }` is a labeled block statement (exitable via `break :blk`). At
+	// statement start, `Identifier ':'` (a single colon, not `::`) opens one.
+	if current(parser).kind == .Identifier && peek(parser).kind == .Colon {
+		label := parse_optional_loop_label(parser)
+		return parse_block_statement(parser, label)
+	}
 
 	if current(parser).kind == .Identifier || current(parser).kind == .Underscore {
 		start_cursor := parser.cursor

compiler_tests.odin

@@ -2133,8 +2133,9 @@ yield_compiles_and_runs :: proc(t: ^testing.T) {
 	state := run_executable(output)
 	// Value blocks, value if-statements (incl. `return` branches and unwrap-`if`),
 	// `orelse`, value loops, labeled value blocks (`blk: { … yield :blk v }`, incl.
-	// defer-capture and `{T,none}` → optional), and outer-loop control (`yield :outer v`
-	// and `break :outer` from an inner loop) together produce 42.
+	// defer-capture, `{T,none}` → optional, and `none` before a concrete yield that uses a
+	// block local), outer-loop control (`yield :outer v` / `break :outer`), and labeled
+	// block statements exited via `break :blk` together produce 42.
 	testing.expect_value(t, state.exit_code, 42)
 }
 
@@ -2182,7 +2183,8 @@ yield_control_flow_is_diagnosed :: proc(t: ^testing.T) {
 	// Value if/loop/block misuse: an `if` value without an `else`; a branch that neither
 	// yields nor exits on every path (20.6); a value loop whose body lacks a trailing
 	// fall-through `yield`; a `yield :label` with no matching value loop; a labeled value
-	// block that does not yield on every path, and a `break :label` naming no loop (20.7).
+	// block that does not yield on every path; a `break :label` naming no loop; and a
+	// `continue :label` targeting a block (not a loop).
 	text := `main :: func() i32 {
 	noelse :: if (true) {
 		yield 1
@@ -2205,6 +2207,9 @@ yield_control_flow_is_diagnosed :: proc(t: ^testing.T) {
 	for 0..10 |m| {
 		break :nope
 	}
+	scope: {
+		continue :scope
+	}
 	return noelse + badbranch + noloopyield + noblockyield
 }
 `
@@ -2226,6 +2231,7 @@ yield_control_flow_is_diagnosed :: proc(t: ^testing.T) {
 	stray_label := false
 	block_no_yield := false
 	bad_break_label := false
+	continue_block := false
 	for diagnostic in diagnostics.items {
 		no_else = no_else || strings.contains(diagnostic.message, "an 'if' used as a value must have an 'else'")
 		branch_no_yield = branch_no_yield || strings.contains(diagnostic.message, "a value branch must end with 'yield' or exit on every path")
@@ -2233,6 +2239,8 @@ yield_control_flow_is_diagnosed :: proc(t: ^testing.T) {
 		stray_label = stray_label || strings.contains(diagnostic.message, "no enclosing value loop or block is labeled 'stray'")
 		block_no_yield = block_no_yield || strings.contains(diagnostic.message, "a labeled value block must 'yield' on every path")
 		bad_break_label = bad_break_label || strings.contains(diagnostic.message, "no enclosing loop is labeled 'nope'")
+		// `continue :scope` targets a labeled block, which is not a loop.
+		continue_block = continue_block || strings.contains(diagnostic.message, "no enclosing loop is labeled 'scope'")
 	}
 	testing.expect(t, no_else)
 	testing.expect(t, branch_no_yield)
@@ -2240,6 +2248,7 @@ yield_control_flow_is_diagnosed :: proc(t: ^testing.T) {
 	testing.expect(t, stray_label)
 	testing.expect(t, block_no_yield)
 	testing.expect(t, bad_break_label)
+	testing.expect(t, continue_block)
 }
 
 @(test)

examples/programs/yield/main.bro

@@ -240,6 +240,45 @@ break_outer :: func() i32 {
 	return count # 5
 }
 
+# A labeled block *statement* (not a value source): `break :blk` exits it early.
+stmt_block :: func(early i32) i32 {
+	x i32 = 0
+	blk: {
+		x = 1
+		if (early == 1) break :blk
+		x = 2
+	}
+	return x # early == 1 -> 1, else 2
+}
+
+# `break :search` escapes a nested loop and the block in one jump; the block's
+# defer still runs on the way out.
+stmt_block_escape :: func() i32 {
+	hits i32 = 0
+	search: {
+		defer hits += 1000
+		for 0..10 |i| {
+			hits += 1
+			if (i == 3) break :search
+		}
+		hits += 100 # skipped by break :search
+	}
+	return hits # 4 + 1000 (defer) = 1004
+}
+
+# Item B: a `none` yielded before a concrete `yield :blk` that references a block local.
+lblock_local :: func() i32 {
+	r :: blk: {
+		val :: 9
+		if (false) yield :blk none
+		yield :blk val
+	}
+	if r |v| {
+		return v
+	}
+	return -1
+}
+
 main :: func() i32 {
 	if (basic() != 42) return 101
 	if (typed() != 100) return 102
@@ -276,5 +315,10 @@ main :: func() i32 {
 	if (yield_outer(99) != -1) return 129
 	if (break_outer() != 5) return 130
 
+	if (stmt_block(1) != 1) return 131
+	if (stmt_block(0) != 2) return 132
+	if (stmt_block_escape() != 1004) return 133
+	if (lblock_local() != 9) return 134
+
 	return 42
 }