[CodeComplete] Fix a crash in preferred type and signature help

[ilya-biryukov]

Summary

Null type pointers could be dereferenced in some cases.

[ilya-biryukov]

• Rename the test, tweak assert comment

[merge_guards_bot]

Build result: pass - 60699 tests passed, 0 failed and 726 were skipped.

Log files: console-log.txt, CMakeCache.txt

clang/lib/Parse/ParseExprCXX.cpp

if (Tok.is(tok::l_brace)) {
     T.consumeOpen();
 
     PreferredType.enterTypeCast(Tok.getLocation(), TypeRep.get());
 
     ExprVector Exprs;
     CommaLocsTy CommaLocs;
 
     auto RunSignatureHelp = [&]() {
-      QualType PreferredType = Actions.ProduceConstructorSignatureHelp(
+      QualType PreferredType;
+      if (TypeRep)
+        PreferredType = Actions.ProduceConstructorSignatureHelp(
             getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
             DS.getEndLoc(), Exprs, T.getOpenLocation());
       CalledSignatureHelp = true;
       return PreferredType;
     };
 
     if (Tok.isNot(tok::r_paren)) {
       if (ParseExpressionList(Exprs, CommaLocs, [&] {
             PreferredType.enterFunctionArgument(Tok.getLocation(),
                                                 RunSignatureHelp);
if (Tok.is(tok::l_paren)) {
     BalancedDelimiterTracker T(*this, tok::l_paren);
     T.consumeOpen();
     ConstructorLParen = T.getOpenLocation();
     if (Tok.isNot(tok::r_paren)) {
       CommaLocsTy CommaLocs;
       auto RunSignatureHelp = [&]() {
         ParsedType TypeRep =
             Actions.ActOnTypeName(getCurScope(), DeclaratorInfo).get();
+        assert(TypeRep && "invalid types should be handled before");
         QualType PreferredType = Actions.ProduceConstructorSignatureHelp(
             getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
             DeclaratorInfo.getEndLoc(), ConstructorArgs, ConstructorLParen);
         CalledSignatureHelp = true;
         return PreferredType;
       };
       if (ParseExpressionList(ConstructorArgs, CommaLocs, [&] {
             PreferredType.enterFunctionArgument(Tok.getLocation(),

clang/unittests/Sema/CodeCompleteTest.cpp

Code = R"cpp(
     int foo(int);
 
     void test() {
       accepts_vector(^::^vector<decltype(foo(1))>::^self);
     }
   )cpp";
   EXPECT_THAT(collectPreferredTypes(Code), Each("vector<int>"));
 }
+
+TEST(PreferredTypeTest, NoCrashOnInvalidTypes) {
+  StringRef Code = R"cpp(
+    auto x = decltype(&1)(^);
+    auto y = new decltype(&1)(^);
+  )cpp";
+  EXPECT_THAT(collectPreferredTypes(Code), Each("NULL TYPE"));
+}
 } // namespace