errdefer and try/defer fix

compiler/parser/parser.odin

@@ -1410,18 +1410,44 @@ parse_block_statement :: proc(parser: ^Parser, label := symbol.INVALID) -> ast.S
 	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`.
+// `defer <statement>` runs whenever the enclosing scope exits; `errdefer`
+// runs only when it exits through a function error and may capture that error.
 parse_defer :: proc(parser: ^Parser) -> ast.Stmt_Id {
-	marker := advance(parser) // consume 'defer'
+	marker := advance(parser)
+	error_only := marker.kind == .Keyword_Errdefer
 	skip_newlines(parser)
+	captures: []symbol.Id
+	if error_only {
+		if _, ok := allow(parser, .Pipe); ok {
+			capture := current(parser)
+			if capture.kind != .Identifier && capture.kind != .Underscore {
+				source.add(parser.diagnostics, capture.span, "expected an errdefer capture name")
+			} else {
+				advance(parser)
+				captures = make([]symbol.Id, 1, parser.module.allocator)
+				captures[0] = capture.symbol
+			}
+			if current(parser).kind == .Comma {
+				source.add(parser.diagnostics, current(parser).span, "'errdefer' accepts exactly one capture")
+				for current(parser).kind != .Pipe && current(parser).kind != .Newline &&
+				    current(parser).kind != .Eof {
+					advance(parser)
+				}
+			}
+			if _, close_ok := allow(parser, .Pipe); !close_ok {
+				source.add(parser.diagnostics, current(parser).span, "expected '|' after errdefer capture")
+			}
+			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,
+		error_only=error_only,
+		captures=captures,
 		expr=ast.INVALID_EXPR,
 		diagnostic=source.INVALID_DIAGNOSTIC,
 	})
@@ -1486,7 +1512,7 @@ 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 {
+	if current(parser).kind == .Keyword_Defer || current(parser).kind == .Keyword_Errdefer {
 		return parse_defer(parser)
 	}
 	if current(parser).kind == .Keyword_Yield {