add defer

TODO.md

@@ -286,9 +286,24 @@
   - the LLVM emitter opens a fresh recovery block after any terminator (not just `ret`),
     so dead code following a `break`/`continue` branch stays well-formed
 
-19. add `defer` statement (inspired by zig)
-  - now unblocked: `defer` reuses the loop-target stack and loop tracking added in
-    milestone 18 to flush deferred statements on `break`/`continue` exits too
+19. add `defer` statement (inspired by zig) (implemented; also adds bare block statements)
+  - `defer <stmt>` runs the statement when the enclosing block scope exits, in reverse
+    (LIFO) order, on every exit path: fall-through, `return`, `break`, `continue`. The
+    deferred statement may be a block (`defer { ... }`)
+  - bare block statements `{ ... }` were added as the enabling feature: a `{ ... }`
+    introduces a nested scope (locals are name-scoped to it; defers inside it fire at the
+    closing brace). A leading `{` is unambiguous since struct literals are postfix only
+  - the return value is captured *before* defers run (a `defer` that mutates the returned
+    local can't change what is returned) — the checker spills the return value into a temp
+    local, then flushes, matching Zig
+  - `return` flushes all active defers; `break`/`continue` flush only down to and including
+    the innermost loop body; fall-through flushes the current block's own defers. Deferring
+    a `return`/`break`/`continue`/`defer`, a `return` inside a `defer`, or a `break`/
+    `continue` that would escape a `defer` are all rejected
+  - implemented entirely in lexer/parser/checker (new `Keyword_Defer`; `Block`/`Defer` AST
+    kinds reusing `body`/`update`; `parse_block_statement`/`parse_defer`). No HIR opcode:
+    a bare block is built and spliced inline, and a deferred statement is built once at the
+    `defer` site and its hir replayed at each exit, so lowering/codegen are unchanged
 
 20. add `yield` statement (see below)
 

compiler/ast/ast.odin

@@ -131,6 +131,8 @@ Stmt_Kind :: enum u8 {
 	For,
 	Break,
 	Continue,
+	Block,
+	Defer,
 }
 
 Assignment_Op :: enum u8 {
@@ -165,6 +167,9 @@ Stmt :: struct {
 	// `For` statements use `expr` as the iterable, `name` as the item capture,
 	// `index_name` as the optional index capture, and `pointer_capture` to
 	// distinguish `|@item|` from copy capture.
+	// `Block` statements (a bare `{ ... }` scope) use `body` as their statements.
+	// `Defer` statements use `update` as the deferred statement (which may itself
+	// be a `Block`).
 	captures:   []symbol.Id,
 	guard:      Expr_Id,
 	body:       []Stmt_Id,

compiler/checker/checker.odin

@@ -68,9 +68,18 @@ Build_Ctx :: struct {
 	global_reads: ^[dynamic]hir.Global_Id,
 	calls:        ^[dynamic]hir.Function_Id,
 	problematic:  ^bool,
-	// Number of enclosing loops being built. `break`/`continue` are only valid
-	// when this is > 0; bumped around loop-body builds in `build_block`.
-	loop_depth:   int,
+	// `defer` lowering. Deferred statements are built once at the `defer` site and
+	// their hir stmt ids stored here as a flat stack across scopes (one entry per
+	// deferred statement); they are replayed (appended) at each scope exit in LIFO
+	// order. `loop_defer_starts` records `len(defers)` at each enclosing loop body
+	// entry: `break`/`continue` flush down to that mark (and need `len > loop_floor`
+	// to be valid). `defer_depth`/`loop_floor` guard control flow inside a deferred
+	// statement: `return` is rejected while `defer_depth > 0`, and `break`/`continue`
+	// only see loops opened within the defer (those past `loop_floor`).
+	defers:            ^[dynamic][]hir.Stmt_Id,
+	loop_defer_starts: ^[dynamic]int,
+	defer_depth:       int,
+	loop_floor:        int,
 }
 
 Constant_Kind :: enum {
@@ -737,6 +746,11 @@ mark_block_imports_used :: proc(checker: ^Checker, statements: []ast.Stmt_Id, fi
 		case .For:
 			mark_expr_imports_used(checker, statement.expr, file)
 			mark_block_imports_used(checker, statement.body, file)
+		case .Block:
+			mark_block_imports_used(checker, statement.body, file)
+		case .Defer:
+			deferred := [1]ast.Stmt_Id{statement.update}
+			mark_block_imports_used(checker, deferred[:], file)
 		case .Break, .Continue:
 		case .Invalid:
 		}
@@ -1875,6 +1889,11 @@ infer_statements :: proc(
 			}
 			infer_statements(checker, statement.body, locals, local_types, pkg, file, demanded, result, result_hint)
 			resize(locals, capture_start)
+		case .Block:
+			infer_statements(checker, statement.body, locals, local_types, pkg, file, demanded, result, result_hint)
+		case .Defer:
+			deferred := [1]ast.Stmt_Id{statement.update}
+			infer_statements(checker, deferred[:], locals, local_types, pkg, file, demanded, result, result_hint)
 		}
 	}
 	resize(locals, scope_start)
@@ -3962,6 +3981,17 @@ make_link_name :: proc(checker: ^Checker, id: Spec_Id) -> string {
 	return fmt.aprintf("%s", strings.to_string(builder), allocator = checker.allocator)
 }
 
+// Replay the deferred statements in frames `[lo, len(defers))` into `body`,
+// innermost-most-recent first (LIFO across frames); each frame's own statements
+// keep their forward order. Used at every scope-exit path in `build_block`.
+flush_defers :: proc(ctx: ^Build_Ctx, body: ^[dynamic]hir.Stmt_Id, lo: int) {
+	for i := len(ctx.defers^) - 1; i >= lo; i -= 1 {
+		for stmt_id in ctx.defers^[i] {
+			append(body, stmt_id)
+		}
+	}
+}
+
 build_block :: proc(
 	ctx: ^Build_Ctx,
 	statements: []ast.Stmt_Id,
@@ -3971,6 +4001,7 @@ build_block :: proc(
 	body: [dynamic]hir.Stmt_Id
 	body.allocator = checker.allocator
 	scope_start := len(ctx.locals^)
+	defer_start := len(ctx.defers^)
 	duplicate_start := scope_start if duplicate_scope_start < 0 else duplicate_scope_start
 	for statement_id in statements {
 		statement := checker.ast_module.statements[statement_id]
@@ -4224,6 +4255,16 @@ build_block :: proc(
 			})
 			ctx.problematic^ = ctx.problematic^ || checker.module.exprs[value].kind == .Invalid
 		case .Return:
+			if ctx.defer_depth > 0 {
+				id := source.add(checker.diagnostics, statement.span, "cannot 'return' inside a 'defer'")
+				append(&body, hir.stmt_id(len(checker.module.statements)))
+				append(&checker.module.statements, hir.Stmt{
+					kind = .Trap, span = statement.span, expr = hir.INVALID_EXPR,
+					local = hir.INVALID_LOCAL, diagnostic = id,
+				})
+				ctx.problematic^ = true
+				continue
+			}
 			if statement.expr == ast.INVALID_EXPR {
 				if !types.is_void(ctx.result) {
 					id := source.add(checker.diagnostics, statement.span, "'return _' is only valid in a void function")
@@ -4234,6 +4275,7 @@ build_block :: proc(
 					})
 					ctx.problematic^ = true
 				} else {
+					flush_defers(ctx, &body, 0)
 					append(&body, hir.stmt_id(len(checker.module.statements)))
 					append(&checker.module.statements, hir.Stmt{
 						kind = .Return, span = statement.span, expr = hir.INVALID_EXPR,
@@ -4257,12 +4299,32 @@ build_block :: proc(
 				ctx.result, ctx.pkg, ctx.file,
 			)
 			value = coerce_expr(checker, value, ctx.result, statement.span)
+			ctx.problematic^ = ctx.problematic^ || checker.module.exprs[value].kind == .Invalid
+			// Run deferred statements before returning, but capture the return value
+			// first (spill it to a temp) so a defer that mutates the returned local
+			// can't change what is returned — Zig evaluates the return value, then
+			// runs defers.
+			if len(ctx.defers^) > 0 {
+				if checker.module.exprs[value].kind != .Invalid {
+					tmp := hir.local_id(len(ctx.hir_locals^))
+					append(ctx.hir_locals, hir.Local{name = checker.sink_symbol, type = ctx.result, mutable = false})
+					append(&body, hir.stmt_id(len(checker.module.statements)))
+					append(&checker.module.statements, hir.Stmt{
+						kind = .Declaration, span = statement.span, local = tmp, expr = value,
+						diagnostic = source.INVALID_DIAGNOSTIC,
+					})
+					value = hir.expr_id(len(checker.module.exprs))
+					append(&checker.module.exprs, hir.Expr{
+						kind = .Local, span = statement.span, type = ctx.result, target = hir.local_ref(tmp),
+					})
+				}
+				flush_defers(ctx, &body, 0)
+			}
 			append(&body, hir.stmt_id(len(checker.module.statements)))
 			append(&checker.module.statements, hir.Stmt{
 				kind = .Return, span = statement.span, expr = value,
 				local = hir.INVALID_LOCAL, diagnostic = source.INVALID_DIAGNOSTIC,
 			})
-			ctx.problematic^ = ctx.problematic^ || checker.module.exprs[value].kind == .Invalid
 		case .Expression:
 			value := build_expr(checker, statement.expr, ctx.locals^[:], ctx.global_reads, ctx.calls, types.INVALID, ctx.pkg, ctx.file)
 			if !types.is_void(checker.module.exprs[value].type) {
@@ -4443,9 +4505,9 @@ build_block :: proc(
 				condition = invalid_hir_expr(checker, statement.span, id, types.BOOL)
 				ctx.problematic^ = true
 			}
-			ctx.loop_depth += 1
+			append(ctx.loop_defer_starts, len(ctx.defers^))
 			loop_body := build_block(ctx, statement.body)
-			ctx.loop_depth -= 1
+			pop(ctx.loop_defer_starts)
 			update := hir.INVALID_STMT
 			if statement.update != ast.INVALID_STMT {
 				update_ast := [1]ast.Stmt_Id{statement.update}
@@ -4537,9 +4599,9 @@ build_block :: proc(
 					append(ctx.locals, Build_Local{name=statement.index_name, type=types.USIZE, mutable=false, id=index_local})
 				}
 			}
-			ctx.loop_depth += 1
+			append(ctx.loop_defer_starts, len(ctx.defers^))
 			loop_body := build_block(ctx, statement.body, capture_start)
-			ctx.loop_depth -= 1
+			pop(ctx.loop_defer_starts)
 			resize(ctx.locals, capture_start)
 
 			append(&body, hir.stmt_id(len(checker.module.statements)))
@@ -4571,7 +4633,9 @@ build_block :: proc(
 				ctx.problematic^ = true
 			}
 		case .Break, .Continue:
-			if ctx.loop_depth == 0 {
+			// Inside a `defer`, `loop_floor` hides the enclosing loops so only loops
+			// opened within the defer count.
+			if len(ctx.loop_defer_starts^) <= ctx.loop_floor {
 				keyword := "break" if statement.kind == .Break else "continue"
 				id := source.addf(checker.diagnostics, statement.span, "'%s' outside of a loop", keyword)
 				append(&body, hir.stmt_id(len(checker.module.statements)))
@@ -4582,12 +4646,50 @@ build_block :: proc(
 				ctx.problematic^ = true
 				continue
 			}
+			// Exit the loop body and any blocks between here and it: run their
+			// deferred statements down to and including the innermost loop body.
+			flush_defers(ctx, &body, ctx.loop_defer_starts^[len(ctx.loop_defer_starts^) - 1])
 			append(&body, hir.stmt_id(len(checker.module.statements)))
 			append(&checker.module.statements, hir.Stmt{
 				kind = .Break if statement.kind == .Break else .Continue,
 				span = statement.span, expr = hir.INVALID_EXPR,
 				local = hir.INVALID_LOCAL, diagnostic = source.INVALID_DIAGNOSTIC,
 			})
+		case .Block:
+			// 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)
+			for stmt in block {
+				append(&body, stmt)
+			}
+			delete(block, checker.allocator)
+		case .Defer:
+			deferred := checker.ast_module.statements[statement.update]
+			if deferred.kind == .Return || deferred.kind == .Break ||
+			   deferred.kind == .Continue || deferred.kind == .Defer {
+				keyword := "return"
+				if deferred.kind == .Break    { keyword = "break" }
+				if deferred.kind == .Continue { keyword = "continue" }
+				if deferred.kind == .Defer    { keyword = "defer" }
+				id := source.addf(checker.diagnostics, statement.span, "cannot defer a '%s' statement", keyword)
+				append(&body, hir.stmt_id(len(checker.module.statements)))
+				append(&checker.module.statements, hir.Stmt{
+					kind = .Trap, span = statement.span, expr = hir.INVALID_EXPR,
+					local = hir.INVALID_LOCAL, diagnostic = id,
+				})
+				ctx.problematic^ = true
+				continue
+			}
+			// Build the deferred statement once, guarded so a `return` inside it is
+			// rejected and `break`/`continue` only target loops opened within the
+			// defer; its hir is replayed at each scope exit, not emitted here.
+			saved_floor := ctx.loop_floor
+			ctx.defer_depth += 1
+			ctx.loop_floor = len(ctx.loop_defer_starts^)
+			entry := build_block(ctx, []ast.Stmt_Id{statement.update})
+			ctx.loop_floor = saved_floor
+			ctx.defer_depth -= 1
+			append(ctx.defers, entry)
 		case .Invalid:
 			append(&body, hir.stmt_id(len(checker.module.statements)))
 			append(&checker.module.statements, hir.Stmt{
@@ -4597,6 +4699,18 @@ build_block :: proc(
 			ctx.problematic^ = true
 		}
 	}
+	// Normal fall-through exit: run this block's own deferred statements, unless
+	// every path already exited early (return/break/continue) — that would only
+	// emit unreachable duplicates.
+	if !all_paths_exit(&checker.module, body[:]) {
+		flush_defers(ctx, &body, defer_start)
+	}
+	// Free this block's deferred-statement entry slices (their stmt ids were already
+	// replayed at every path that can leave this block) and pop the frame.
+	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 body[:]
 }
@@ -4652,6 +4766,34 @@ loop_body_breaks :: proc(module: ^hir.Module, stmts: []hir.Stmt_Id) -> bool {
 	return false
 }
 
+// Like `all_paths_return`, but also treats `break`/`continue` as terminating the
+// block. Used only to decide whether `build_block` may skip the fall-through defer
+// flush (a block that always exits early would otherwise emit unreachable copies).
+all_paths_exit :: proc(module: ^hir.Module, stmts: []hir.Stmt_Id) -> bool {
+	for id in stmts {
+		statement := module.statements[id]
+		#partial switch statement.kind {
+		case .Return, .Trap, .Break, .Continue:
+			return true
+		case .If:
+			if statement.else_body != nil &&
+			   all_paths_exit(module, statement.then_body) &&
+			   all_paths_exit(module, statement.else_body) {
+				return true
+			}
+		case .While:
+			if statement.expr != hir.INVALID_EXPR && int(statement.expr) < len(module.exprs) {
+				condition := module.exprs[statement.expr]
+				if condition.kind == .Bool && condition.integer != 0 &&
+				   !loop_body_breaks(module, statement.then_body) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
 build_function :: proc(checker: ^Checker, id: Spec_Id) {
 	spec := checker.specs[id]
 	function := checker.ast_module.functions[spec.template]
@@ -4751,6 +4893,10 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 			},
 		)
 	}
+	defers: [dynamic][]hir.Stmt_Id
+	defers.allocator = checker.allocator
+	loop_defer_starts: [dynamic]int
+	loop_defer_starts.allocator = checker.allocator
 	ctx := Build_Ctx{
 		checker = checker,
 		pkg = function.pkg,
@@ -4762,6 +4908,8 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 		global_reads = &global_reads,
 		calls = &calls,
 		problematic = &problematic,
+		defers = &defers,
+		loop_defer_starts = &loop_defer_starts,
 	}
 	block := build_block(&ctx, function.body)
 	returns := all_paths_return(&checker.module, block)
@@ -4806,6 +4954,11 @@ build_function :: proc(checker: ^Checker, id: Spec_Id) {
 			diagnostic = source.INVALID_DIAGNOSTIC,
 		},
 	)
+	for entry in defers {
+		delete(entry, checker.allocator)
+	}
+	delete(defers)
+	delete(loop_defer_starts)
 	delete(locals)
 }
 

compiler/lexer/lexer.odin

@@ -34,6 +34,7 @@ keyword_kind :: proc(text: string) -> token.Kind {
 	case "for":           return .Keyword_For
 	case "break":         return .Keyword_Break
 	case "continue":      return .Keyword_Continue
+	case "defer":         return .Keyword_Defer
 	case "else":          return .Keyword_Else
 	case "true":          return .Keyword_True
 	case "false":         return .Keyword_False

compiler/parser/parser.odin

@@ -1001,6 +1001,41 @@ parse_loop_control :: proc(parser: ^Parser, kind: ast.Stmt_Kind) -> ast.Stmt_Id
 	return 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 {
+	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,
+		body=body,
+		expr=ast.INVALID_EXPR,
+		update=ast.INVALID_STMT,
+		diagnostic=source.INVALID_DIAGNOSTIC,
+	})
+	return id
+}
+
+// `defer <statement>` runs the statement when the enclosing scope exits. The
+// statement may be a block (`defer { ... }`). The checker rejects deferring a
+// `return`/`break`/`continue`/`defer`.
+parse_defer :: proc(parser: ^Parser) -> ast.Stmt_Id {
+	marker := advance(parser) // consume 'defer'
+	skip_newlines(parser)
+	inner := parse_statement(parser)
+	id := ast.stmt_id(len(parser.module.statements))
+	append(&parser.module.statements, ast.Stmt{
+		kind=.Defer,
+		span=marker.span,
+		update=inner,
+		expr=ast.INVALID_EXPR,
+		diagnostic=source.INVALID_DIAGNOSTIC,
+	})
+	return id
+}
+
 starts_declared_type :: proc(parser: ^Parser) -> bool {
 	if current(parser).kind != .Left_Bracket {
 		return is_type_token(current(parser).kind)
@@ -1045,6 +1080,13 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	if current(parser).kind == .Keyword_Continue {
 		return parse_loop_control(parser, .Continue)
 	}
+	if current(parser).kind == .Keyword_Defer {
+		return parse_defer(parser)
+	}
+	// A leading `{` opens a bare block scope (struct literals are postfix only).
+	if current(parser).kind == .Left_Brace {
+		return parse_block_statement(parser)
+	}
 
 	if current(parser).kind == .Identifier || current(parser).kind == .Underscore {
 		start_cursor := parser.cursor
@@ -1333,7 +1375,7 @@ parse_while_update :: proc(parser: ^Parser) -> ast.Stmt_Id {
 		statement := &parser.module.statements[update]
 		switch statement.kind {
 		case .Assignment, .Expression:
-		case .Invalid, .Declaration, .Return, .If, .While, .For, .Break, .Continue:
+		case .Invalid, .Declaration, .Return, .If, .While, .For, .Break, .Continue, .Block, .Defer:
 			diagnostic := source.add(
 				parser.diagnostics,
 				statement.span,

compiler/token/token.odin

@@ -69,6 +69,7 @@ Kind :: enum u8 {
 	Keyword_For,
 	Keyword_Break,
 	Keyword_Continue,
+	Keyword_Defer,
 	Keyword_Else,
 	Keyword_True,
 	Keyword_False,

compiler_tests.odin

@@ -2061,6 +2061,69 @@ missing_return :: func() i32 {
 	testing.expect(t, missing)
 }
 
+@(test)
+defer_compiles_and_runs :: proc(t: ^testing.T) {
+	output := "/tmp/brolang-test-defer"
+	defer _ = os.remove(output)
+	status := compiler_core.compile_package("examples/programs/defer", output)
+	testing.expect_value(t, status, 0)
+	state := run_executable(output)
+	// LIFO, runs on fall-through / break / continue / return (with the return value
+	// captured before defers run), scoped bare blocks, and `defer { ... }` blocks
+	// together produce 42.
+	testing.expect_value(t, state.exit_code, 42)
+}
+
+@(test)
+defer_misuse_is_diagnosed :: proc(t: ^testing.T) {
+	// Deferring control flow that would escape the defer is rejected: `defer return`,
+	// `defer break`, and a `return` inside a `defer { ... }` block.
+	text := `main :: func() i32 {
+	bad_defer_return()
+	bad_defer_break()
+	bad_return_in_defer()
+	return 0
+}
+bad_defer_return :: func() void {
+	defer return
+}
+bad_defer_break :: func() void {
+	for 0..3 |i| {
+		defer break
+		_ = i
+	}
+}
+bad_return_in_defer :: func() void {
+	defer {
+		return
+	}
+}
+`
+	source_file := source.Source{path="test.bro", text=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)
+
+	defer_return := false
+	defer_break := false
+	return_in_defer := false
+	for diagnostic in diagnostics.items {
+		defer_return = defer_return || strings.contains(diagnostic.message, "cannot defer a 'return' statement")
+		defer_break = defer_break || strings.contains(diagnostic.message, "cannot defer a 'break' statement")
+		return_in_defer = return_in_defer || strings.contains(diagnostic.message, "cannot 'return' inside a 'defer'")
+	}
+	testing.expect(t, defer_return)
+	testing.expect(t, defer_break)
+	testing.expect(t, return_in_defer)
+}
+
 @(test)
 foreign_function_links_from_c_source :: proc(t: ^testing.T) {
 	output := "/tmp/brolang-test-foreign-source"

examples/programs/defer/main.bro

@@ -0,0 +1,82 @@
+# Milestone 19: `defer` and bare block statements.
+#
+# `defer <stmt>` runs the statement when the enclosing scope exits, in reverse
+# (LIFO) order, on every exit path. A bare `{ ... }` introduces a scope. Each
+# section returns a distinct code on failure; success falls through to 42.
+
+# The return value is captured before defers run, so the mutation here does not
+# change what is returned (Zig semantics).
+spill_check :: func() i32 {
+	x i32 = 5
+	defer x = 999
+	return x
+}
+
+# A function-scope defer runs only at function exit; a `break` runs the loop-body
+# defer but NOT the enclosing function-scope defer.
+enclosing_defer_check :: func() i32 {
+	v i32 = 0
+	defer v = v + 100
+	for 0..3 |i| {
+		defer v = v + 1
+		if (i == 1) break
+	}
+	return v # 0->1 (i=0 fall-through), ->2 (i=1 break); the +100 runs after capture
+}
+
+main :: func() i32 {
+	# 1. return value captured before defers run.
+	if (spill_check() != 5) return 101
+
+	# 2. LIFO ordering, run at end of each loop iteration.
+	r i32 = 0
+	for 0..1 |i| {
+		defer r = r * 2 + 1 # registered first -> runs last
+		defer r = r * 2     # registered second -> runs first
+		_ = i
+	}
+	if (r != 1) return 102 # 0 -> (r*2)=0 -> (r*2+1)=1 ; FIFO would give 2
+
+	# 3. scoped bare block + scoped defer (defer fires at the closing brace, and
+	#    the block-local is not visible afterwards).
+	a i32 = 1
+	{
+		defer a = 4
+		c i32 = 3
+		_ = c
+	}
+	if (a != 4) return 103
+
+	# 4. `defer { ... }` block: all its statements run (in order) at scope close.
+	s i32 = 0
+	{
+		defer {
+			s = s + 1
+			s = s * 10
+		}
+		s = 5
+	}
+	if (s != 60) return 104 # 5 -> 6 -> 60
+
+	# 5. `break` flushes the loop-body defer.
+	bc i32 = 0
+	for 0..5 |i| {
+		defer bc = bc + 1
+		if (i == 2) break
+	}
+	if (bc != 3) return 105 # i=0,1 fall-through + i=2 break
+
+	# 6. `continue` flushes the loop-body defer.
+	cc i32 = 0
+	for 0..3 |i| {
+		defer cc = cc + 1
+		if (i == 1) continue
+		cc = cc + 10
+	}
+	if (cc != 23) return 106 # 10,+1 ; +1 (continue) ; +10,+1
+
+	# 7. break does not run an enclosing function-scope defer.
+	if (enclosing_defer_check() != 2) return 107
+
+	return 42
+}