From 0fa8cf44f69dcb00dacf180d88ebfa09bc462120 Mon Sep 17 00:00:00 2001
From: mlugg <mlugg@mlugg.co.uk>
Date: Sat, 16 Sep 2023 22:38:47 +0100
Subject: [PATCH] translate-c: do not translate macros which use arguments as
 struct/union/enum names

Consider this C macro:
```c
#define FOO(x) struct x
```

Previously, translate-c did not detect that the `x` in the body referred
to the argument, so wrongly translated this code as using the
nonexistent `struct_x`. Since undefined identifiers are noticed in
AstGen, this prevents the translated file from being usable at all.

translate-c now instead detects this case and emits an appropriate
compile error in the macro's place.
---
 src/translate_c.zig  | 32 ++++++++++++++++++++++++++------
 test/translate_c.zig |  6 ++++++
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/translate_c.zig b/src/translate_c.zig
index 93c85ab8bd..b8b221301c 100644
--- a/src/translate_c.zig
+++ b/src/translate_c.zig
@@ -5524,22 +5524,38 @@ const MacroCtx = struct {
         return MacroSlicer{ .source = self.source, .tokens = self.list };
     }
 
-    fn containsUndefinedIdentifier(self: *MacroCtx, scope: *Scope, params: []const ast.Payload.Param) ?[]const u8 {
+    const MacroTranslateError = union(enum) {
+        undefined_identifier: []const u8,
+        invalid_arg_usage: []const u8,
+    };
+
+    fn checkTranslatableMacro(self: *MacroCtx, scope: *Scope, params: []const ast.Payload.Param) ?MacroTranslateError {
         const slicer = self.makeSlicer();
+        var last_is_type_kw = false;
         var i: usize = 1; // index 0 is the macro name
         while (i < self.list.len) : (i += 1) {
             const token = self.list[i];
             switch (token.id) {
                 .Period, .Arrow => i += 1, // skip next token since field identifiers can be unknown
+                .Keyword_struct, .Keyword_union, .Keyword_enum => if (!last_is_type_kw) {
+                    last_is_type_kw = true;
+                    continue;
+                },
                 .Identifier => {
                     const identifier = slicer.slice(token);
                     const is_param = for (params) |param| {
                         if (param.name != null and mem.eql(u8, identifier, param.name.?)) break true;
                     } else false;
-                    if (!scope.contains(identifier) and !isBuiltinDefined(identifier) and !is_param) return identifier;
+                    if (is_param and last_is_type_kw) {
+                        return .{ .invalid_arg_usage = identifier };
+                    }
+                    if (!scope.contains(identifier) and !isBuiltinDefined(identifier) and !is_param) {
+                        return .{ .undefined_identifier = identifier };
+                    }
                 },
                 else => {},
             }
+            last_is_type_kw = false;
         }
         return null;
     }
@@ -5649,8 +5665,10 @@ fn transPreprocessorEntities(c: *Context, unit: *clang.ASTUnit) Error!void {
 fn transMacroDefine(c: *Context, m: *MacroCtx) ParseError!void {
     const scope = &c.global_scope.base;
 
-    if (m.containsUndefinedIdentifier(scope, &.{})) |ident|
-        return m.fail(c, "unable to translate macro: undefined identifier `{s}`", .{ident});
+    if (m.checkTranslatableMacro(scope, &.{})) |err| switch (err) {
+        .undefined_identifier => |ident| return m.fail(c, "unable to translate macro: undefined identifier `{s}`", .{ident}),
+        .invalid_arg_usage => unreachable, // no args
+    };
 
     const init_node = try parseCExpr(c, m, scope);
     const last = m.next().?;
@@ -5698,8 +5716,10 @@ fn transMacroFnDefine(c: *Context, m: *MacroCtx) ParseError!void {
 
     try m.skip(c, .RParen);
 
-    if (m.containsUndefinedIdentifier(scope, fn_params.items)) |ident|
-        return m.fail(c, "unable to translate macro: undefined identifier `{s}`", .{ident});
+    if (m.checkTranslatableMacro(scope, fn_params.items)) |err| switch (err) {
+        .undefined_identifier => |ident| return m.fail(c, "unable to translate macro: undefined identifier `{s}`", .{ident}),
+        .invalid_arg_usage => |ident| return m.fail(c, "unable to translate macro: untranslatable usage of arg `{s}`", .{ident}),
+    };
 
     const expr = try parseCExpr(c, m, scope);
     const last = m.next().?;
diff --git a/test/translate_c.zig b/test/translate_c.zig
index 3a453b9aa8..3fad7f8fe5 100644
--- a/test/translate_c.zig
+++ b/test/translate_c.zig
@@ -4129,4 +4129,10 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\    }) != 0) {}
         \\}
     });
+
+    cases.add("macro using argument as struct name is not translated",
+        \\#define FOO(x) struct x
+    , &[_][]const u8{
+        \\pub const FOO = @compileError("unable to translate macro: untranslatable usage of arg `x`");
+    });
 }