From 581d292381157464ae6f2c88c8a628314f005742 Mon Sep 17 00:00:00 2001
From: travisstaloch <twostepted@gmail.com>
Date: Fri, 23 Dec 2022 13:10:04 -0800
Subject: [PATCH] fix overflow found while fuzzing

* allow file level `union {}` to parse as tuple field

this was found while fuzzing zls.

* before this patch the input `union {}` crashed the parser.  after
  this, it parses correctly just like `struct {}`.
* adds behavior tests for both inputs `struct {}` and `union {}`,
  checking that each becomes a file level tuple field.
---
 lib/std/zig/Ast.zig                       |  2 +-
 test/behavior.zig                         |  1 +
 test/behavior/empty_file_level_struct.zig |  1 +
 test/behavior/empty_file_level_union.zig  |  1 +
 test/behavior/empty_tuple_fields.zig      | 26 +++++++++++++++++++++++
 5 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 test/behavior/empty_file_level_struct.zig
 create mode 100644 test/behavior/empty_file_level_union.zig
 create mode 100644 test/behavior/empty_tuple_fields.zig

diff --git a/lib/std/zig/Ast.zig b/lib/std/zig/Ast.zig
index c2439437e79914885c19917b119be51367c97a90..74b104847091ac40e71d8f502706b9ac91d7268b 100644
--- a/lib/std/zig/Ast.zig
+++ b/lib/std/zig/Ast.zig
@@ -618,7 +618,7 @@ pub fn firstToken(tree: Ast, node: Node.Index) TokenIndex {
         .tagged_union_enum_tag_trailing,
         => {
             const main_token = main_tokens[n];
-            switch (token_tags[main_token - 1]) {
+            switch (token_tags[main_token -| 1]) {
                 .keyword_packed, .keyword_extern => end_offset += 1,
                 else => {},
             }
diff --git a/test/behavior.zig b/test/behavior.zig
index 4a70cb010b509311217314c02a0ce20d3786bf9f..36403a8f0cad5bead0358b2c3253dc0a7b3648f9 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -151,6 +151,7 @@ test {
     _ = @import("behavior/const_slice_child.zig");
     _ = @import("behavior/decltest.zig");
     _ = @import("behavior/defer.zig");
+    _ = @import("behavior/empty_tuple_fields.zig");
     _ = @import("behavior/empty_union.zig");
     _ = @import("behavior/enum.zig");
     _ = @import("behavior/error.zig");
diff --git a/test/behavior/empty_file_level_struct.zig b/test/behavior/empty_file_level_struct.zig
new file mode 100644
index 0000000000000000000000000000000000000000..86f0f2b3c7f579279b17bab584b232f8002398bf
--- /dev/null
+++ b/test/behavior/empty_file_level_struct.zig
@@ -0,0 +1 @@
+struct {}
diff --git a/test/behavior/empty_file_level_union.zig b/test/behavior/empty_file_level_union.zig
new file mode 100644
index 0000000000000000000000000000000000000000..0d24797ffb6565c4012b5aff0ab04a9860602959
--- /dev/null
+++ b/test/behavior/empty_file_level_union.zig
@@ -0,0 +1 @@
+union {}
diff --git a/test/behavior/empty_tuple_fields.zig b/test/behavior/empty_tuple_fields.zig
new file mode 100644
index 0000000000000000000000000000000000000000..7309dc9b3e9b3b3feb8aa0718d94dab3a3f0b4a3
--- /dev/null
+++ b/test/behavior/empty_tuple_fields.zig
@@ -0,0 +1,26 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+test "empty file level struct" {
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+
+    const T = @import("empty_file_level_struct.zig");
+    const info = @typeInfo(T);
+    try std.testing.expectEqual(@as(usize, 1), info.Struct.fields.len);
+    try std.testing.expectEqualStrings("0", info.Struct.fields[0].name);
+    try std.testing.expect(@typeInfo(info.Struct.fields[0].type) == .Struct);
+}
+
+test "empty file level union" {
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+
+    const T = @import("empty_file_level_union.zig");
+    const info = @typeInfo(T);
+    try std.testing.expectEqual(@as(usize, 1), info.Struct.fields.len);
+    try std.testing.expectEqualStrings("0", info.Struct.fields[0].name);
+    try std.testing.expect(@typeInfo(info.Struct.fields[0].type) == .Union);
+}
-- 
2.54.0