[Clang] disallow # operators in attribute argument lists (#147308)

Fixes #147217

---

This PR addresses the parsing of attribute arguments by diagnosing and
disallowing the `#` operator

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -228,6 +228,12 @@ Improvements to Clang's diagnostics
 - Fixed false positive in ``-Wmissing-noreturn`` diagnostic when it was requiring the usage of
   ``[[noreturn]]`` on lambdas before C++23 (#GH154493).
 
+- Clang now diagnoses the use of ``#`` and ``##`` preprocessor tokens in
+  attribute argument lists in C++ when ``-pedantic`` is enabled. The operators
+  can be used in macro replacement lists with the usual preprocessor semantics,
+  however, non-preprocessor use of tokens now triggers a pedantic warning in C++.
+  Compilation in C mode is unchanged, and still permits these tokens to be used. (#GH147217)
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -830,6 +830,9 @@ def err_ms_property_expected_comma_or_rparen : Error<
   "expected ',' or ')' at end of property accessor list">;
 def err_ms_property_initializer : Error<
   "property declaration cannot have a default member initializer">;
+def ext_invalid_attribute_argument
+    : Extension<"'%0' is not allowed in an attribute argument list">,
+    InGroup<DiagGroup<"attribute-preprocessor-tokens">>;
 
 def err_assume_attr_expects_cond_expr : Error<
   "use of this expression in an %0 attribute requires parentheses">;

clang/lib/Parse/ParseDeclCXX.cpp

@@ -4512,6 +4512,27 @@ bool Parser::ParseCXX11AttributeArgs(
       Form = ParsedAttr::Form::Microsoft();
   }
 
+  if (LO.CPlusPlus) {
+    TentativeParsingAction TPA(*this);
+    bool HasInvalidArgument = false;
+    while (Tok.isNot(tok::r_paren) && Tok.isNot(tok::eof)) {
+      if (Tok.isOneOf(tok::hash, tok::hashhash)) {
+        Diag(Tok.getLocation(), diag::ext_invalid_attribute_argument)
+            << PP.getSpelling(Tok);
+        HasInvalidArgument = true;
+      }
+      ConsumeAnyToken();
+    }
+
+    if (HasInvalidArgument) {
+      SkipUntil(tok::r_paren);
+      TPA.Commit();
+      return true;
+    }
+
+    TPA.Revert();
+  }
+
   // If the attribute isn't known, we will not attempt to parse any
   // arguments.
   if (Form.getSyntax() != ParsedAttr::AS_Microsoft &&

clang/test/Parser/cxx0x-attributes-preprocessor-tokens.cpp

@@ -0,0 +1,58 @@
+// RUN: %clang_cc1 -fsyntax-only -Wattribute-preprocessor-tokens -verify %s
+// RUN: %clang_cc1 -Wattribute-preprocessor-tokens -E %s | FileCheck %s
+// RUN: %clang_cc1 -x c -fsyntax-only -verify=c %s
+// RUN: %clang_cc1 -x c -E %s | FileCheck %s
+
+#define ATTR_STR(X) [[clang::annotate(#X)]]
+#define ATTR_PASTE(X, Y) [[clang::annotate("test", X ## Y)]]
+
+[[clang::assume(#)]] void f1();           // c-error {{expected expression}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}}
+
+[[clang::assume(##)]] void f2();          // c-error {{expected expression}} \
+                                          // expected-warning {{'##' is not allowed in an attribute argument list}}
+
+[[clang::assume(1#2#3)]] void f3();       // c-error {{use of this expression in an 'assume' attribute requires parentheses}} \
+                                          // c-error {{expected ')'}} \
+                                          // c-note {{to match this '('}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(#)]] void f4();        // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(##)]] void f5();       // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'##' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(1#2#3)]] void f6();    // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}} \
+                                          // expected-warning {{'#' is not allowed in an attribute argument list}}
+
+[[clang::assume(%:)]] void f7();          // c-error {{expected expression}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}}
+
+
+[[clang::assume(%:%:)]] void f8();        // c-error {{expected expression}} \
+                                          // expected-warning {{'%:%:' is not allowed in an attribute argument list}}
+
+[[clang::assume(1%:2%:3)]] void f9();     // c-error {{use of this expression in an 'assume' attribute requires parentheses}} \
+                                          // c-error {{expected ')'}} \
+                                          // c-note {{to match this '('}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(%:)]] void f10();      // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(%:%:)]] void f11();    // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'%:%:' is not allowed in an attribute argument list}}
+
+[[unknown::unknown(1%:2%:3)]] void f12(); // c-warning {{unknown attribute 'unknown::unknown' ignored}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}} \
+                                          // expected-warning {{'%:' is not allowed in an attribute argument list}}
+
+ATTR_STR(stringify) void f13();
+// CHECK: {{\[\[}}clang{{::}}annotate("stringify"){{\]\]}} void f13();
+
+ATTR_PASTE(1, 2) void f14();
+// CHECK: {{\[\[}}clang{{::}}annotate("test", 12){{\]\]}} void f14();