translate-c: Escape non-ASCII characters that appear in macros

Macro definitions are simply a slice of bytes, which may not be
UTF-8 encoded. If they are not UTF-8 encoded, escape non-printable
and non-ASCII characters as `\xNN`.

Fixes #12784

src/translate_c.zig

@@ -5957,20 +5957,36 @@ fn zigifyEscapeSequences(ctx: *Context, m: *MacroCtx) ![]const u8 {
     return bytes[0..i];
 }
 
+/// non-ASCII characters (c > 127) are also treated as non-printable by fmtSliceEscapeLower.
+/// If a C string literal or char literal in a macro is not valid UTF-8, we need to escape
+/// non-ASCII characters so that the Zig source we output will itself be UTF-8.
+fn escapeUnprintables(ctx: *Context, m: *MacroCtx) ![]const u8 {
+    const zigified = try zigifyEscapeSequences(ctx, m);
+    if (std.unicode.utf8ValidateSlice(zigified)) return zigified;
+
+    const formatter = std.fmt.fmtSliceEscapeLower(zigified);
+    const encoded_size = @intCast(usize, std.fmt.count("{s}", .{formatter}));
+    var output = try ctx.arena.alloc(u8, encoded_size);
+    return std.fmt.bufPrint(output, "{s}", .{formatter}) catch |err| switch (err) {
+        error.NoSpaceLeft => unreachable,
+        else => |e| return e,
+    };
+}
+
 fn parseCPrimaryExprInner(c: *Context, m: *MacroCtx, scope: *Scope) ParseError!Node {
     const tok = m.next().?;
     const slice = m.slice();
     switch (tok) {
         .CharLiteral => {
             if (slice[0] != '\'' or slice[1] == '\\' or slice.len == 3) {
-                return Tag.char_literal.create(c.arena, try zigifyEscapeSequences(c, m));
+                return Tag.char_literal.create(c.arena, try escapeUnprintables(c, m));
             } else {
                 const str = try std.fmt.allocPrint(c.arena, "0x{s}", .{std.fmt.fmtSliceHexLower(slice[1 .. slice.len - 1])});
                 return Tag.integer_literal.create(c.arena, str);
             }
         },
         .StringLiteral => {
-            return Tag.string_literal.create(c.arena, try zigifyEscapeSequences(c, m));
+            return Tag.string_literal.create(c.arena, try escapeUnprintables(c, m));
         },
         .IntegerLiteral, .FloatLiteral => {
             return parseCNumLit(c, m);

test/behavior/translate_c_macros.zig

@@ -5,6 +5,7 @@ const expectEqual = std.testing.expectEqual;
 const expectEqualStrings = std.testing.expectEqualStrings;
 
 const h = @cImport(@cInclude("behavior/translate_c_macros.h"));
+const latin1 = @cImport(@cInclude("behavior/translate_c_macros_not_utf8.h"));
 
 test "casting to void with a macro" {
     h.IGNORE_ME_1(42);
@@ -134,3 +135,14 @@ test "string literal macro with embedded tab character" {
 
     try expectEqualStrings("hello\t", h.EMBEDDED_TAB);
 }
+
+test "string and char literals that are not UTF-8 encoded. Issue #12784" {
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+
+    try expectEqual(@as(u8, '\xA9'), latin1.UNPRINTABLE_CHAR);
+    try expectEqualStrings("\xA9\xA9\xA9", latin1.UNPRINTABLE_STRING);
+}

test/behavior/translate_c_macros_not_utf8.h

@@ -0,0 +1,5 @@
+// Note: This file is encoded with ISO/IEC 8859-1 (latin1), not UTF-8.
+// Do not change the encoding
+
+#define UNPRINTABLE_STRING "©©©"
+#define UNPRINTABLE_CHAR '©'