From 435ee44e4c79124a93941269e4784df19c201df0 Mon Sep 17 00:00:00 2001
From: Brymer Meneses <68867487+brymer-meneses@users.noreply.github.com>
Date: Fri, 23 Aug 2024 00:21:46 +0800
Subject: [PATCH] Report invalid parse on `var x: i32 = {.7 = 8}` (#4237)

---
 toolchain/parse/handle_period.cpp             |  3 +-
 .../fail_invalid_struct_designator.carbon     | 32 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon

diff --git a/toolchain/parse/handle_period.cpp b/toolchain/parse/handle_period.cpp
index 8ececd7d35cbd..7675a8b0e720b 100644
--- a/toolchain/parse/handle_period.cpp
+++ b/toolchain/parse/handle_period.cpp
@@ -24,7 +24,8 @@ static auto HandlePeriodOrArrow(Context& context, NodeKind node_kind,
   } else if (context.ConsumeAndAddLeafNodeIf(Lex::TokenKind::Base,
                                              NodeKind::BaseName)) {
     // OK, `.base`.
-  } else if (context.ConsumeAndAddLeafNodeIf(Lex::TokenKind::IntLiteral,
+  } else if (node_kind != NodeKind::StructFieldDesignator &&
+             context.ConsumeAndAddLeafNodeIf(Lex::TokenKind::IntLiteral,
                                              NodeKind::IntLiteral)) {
     // OK, '.42'.
   } else if (paren_state != State::Invalid &&
diff --git a/toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon b/toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon
new file mode 100644
index 0000000000000..c2c5c6a3cd8ea
--- /dev/null
+++ b/toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon
@@ -0,0 +1,32 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/struct/fail_invalid_struct_designator.carbon
+
+// CHECK:STDERR: fail_invalid_struct_designator.carbon:[[@LINE+3]]:16: ERROR: Expected identifier after `.`.
+// CHECK:STDERR: var x: i32 = {.7 = 8};
+// CHECK:STDERR:                ^
+var x: i32 = {.7 = 8};
+
+// CHECK:STDOUT: - filename: fail_invalid_struct_designator.carbon
+// CHECK:STDOUT:   parse_tree: [
+// CHECK:STDOUT:     {kind: 'FileStart', text: ''},
+// CHECK:STDOUT:       {kind: 'VariableIntroducer', text: 'var'},
+// CHECK:STDOUT:         {kind: 'IdentifierName', text: 'x'},
+// CHECK:STDOUT:         {kind: 'IntTypeLiteral', text: 'i32'},
+// CHECK:STDOUT:       {kind: 'BindingPattern', text: ':', subtree_size: 3},
+// CHECK:STDOUT:       {kind: 'VariableInitializer', text: '='},
+// CHECK:STDOUT:         {kind: 'StructLiteralStart', text: '{'},
+// CHECK:STDOUT:           {kind: 'IdentifierName', text: '7', has_error: yes},
+// CHECK:STDOUT:         {kind: 'StructFieldDesignator', text: '.', subtree_size: 2},
+// CHECK:STDOUT:         {kind: 'IntLiteral', text: '8'},
+// CHECK:STDOUT:         {kind: 'InvalidParse', text: '=', has_error: yes},
+// CHECK:STDOUT:       {kind: 'StructLiteral', text: '}', has_error: yes, subtree_size: 6},
+// CHECK:STDOUT:     {kind: 'VariableDecl', text: ';', subtree_size: 12},
+// CHECK:STDOUT:     {kind: 'FileEnd', text: ''},
+// CHECK:STDOUT:   ]