[Clang] A lone [ does not an attribute make (#147306)

In some tentative parses, we would always consider `[` as the start of
an attribute - only `[[` should be.

Fixes #63880

Author: cor3ntin

clang/docs/ReleaseNotes.rst

@@ -932,6 +932,7 @@ Bug Fixes to C++ Support
   through its address (``(&Foo::bar<baz>)()``).
 - Correctly handle allocations in the condition of a ``if constexpr``.(#GH120197) (#GH134820)
 - Fixed a crash when handling invalid member using-declaration in C++20+ mode. (#GH63254)
+- Fixed parsing of lambda expressions that appear after ``*`` or ``&`` in contexts where a declaration can appear. (#GH63880)
 - Fix name lookup in lambda appearing in the body of a requires expression. (#GH147650)
 - Fix a crash when trying to instantiate an ambiguous specialization. (#GH51866)
 - Improved handling of variables with ``consteval`` constructors, to

clang/lib/Parse/ParseTentative.cpp

@@ -735,10 +735,12 @@ bool Parser::TrySkipAttributes() {
                      tok::kw_alignas) ||
          Tok.isRegularKeywordAttribute()) {
     if (Tok.is(tok::l_square)) {
+      if (!NextToken().is(tok::l_square))
+        return true;
+
       ConsumeBracket();
-      if (Tok.isNot(tok::l_square))
-        return false;
       ConsumeBracket();
+
       if (!SkipUntil(tok::r_square) || Tok.isNot(tok::r_square))
         return false;
       // Note that explicitly checking for `[[` and `]]` allows to fail as

clang/test/Parser/cxx0x-lambda-expressions.cpp

@@ -159,3 +159,15 @@ struct U {
   template <typename T>
   void m_fn1(T x = 0[0); // expected-error{{expected ']'}} expected-note{{to match this '['}}
 } *U;
+
+
+
+namespace GH63880{
+void f() {
+    char* i(*[] { return new int; }());
+    // expected-error@-1{{cannot initialize a variable of type 'char *' with an lvalue of type 'int'}}
+
+    char* j(&[]() -> int& { return *new int; }());
+    //expected-error@-1{{cannot initialize a variable of type 'char *' with an rvalue of type 'int *'}}
+}
+}