Don't eagerly evaluate the TypeSourceInfo when mangling names.

[zturner]

Summary

Don't eagerly evaluate the TypeSourceInfo while mangling.

A VarDecl may not have TypeSourceInfo, for example if source is
generated in-memory by another application. This patch changes
the mangler to use a default instance if the TypeSourceInfo
doesn't exist.

[majnemer]

LGTM

[dblaikie]

It'd be good to include an explanation (in a comment and/or the commit
message) as to why this is necessary and untested in-tree so when someone
comes back to this they don't remove it for being unnecessary.

[zturner]

majnemer@ caught up with me offline and suggested a different fix, which is to simply call the getSourceRange() method of VarDecl instead of going through the TypeSourceInfo. This also solves the problem, so I will commit this fix instead as it seems more straightforward.

[zturner]

Closed by commit rL211667 (authored by @zturner).

cfe/trunk/lib/AST/MicrosoftMangle.cpp

else if (!VD->isStaticLocal())
     Out << '3';
   else
     Out << '4';
   // Now mangle the type.
   // <variable-type> ::= <type> <cvr-qualifiers>
   //                 ::= <type> <pointee-cvr-qualifiers> # pointers, references
   // Pointers and references are odd. The type of 'int * const foo;' gets
   // mangled as 'QAHA' instead of 'PAHB', for example.
-  TypeLoc TL = VD->getTypeSourceInfo()->getTypeLoc();
+  SourceRange SR = VD->getSourceRange();
   QualType Ty = VD->getType();
   if (Ty->isPointerType() || Ty->isReferenceType() ||
       Ty->isMemberPointerType()) {
-    mangleType(Ty, TL.getSourceRange(), QMM_Drop);
+    mangleType(Ty, SR, QMM_Drop);
     manglePointerExtQualifiers(
         Ty.getDesugaredType(getASTContext()).getLocalQualifiers(), nullptr);
     if (const MemberPointerType *MPT = Ty->getAs<MemberPointerType>()) {
       mangleQualifiers(MPT->getPointeeType().getQualifiers(), true);
       // Member pointers are suffixed with a back reference to the member
       // pointer's class name.
       mangleName(MPT->getClass()->getAsCXXRecordDecl());
     } else
       mangleQualifiers(Ty->getPointeeType().getQualifiers(), false);
   } else if (const ArrayType *AT = getASTContext().getAsArrayType(Ty)) {
     // Global arrays are funny, too.
     mangleDecayedArrayType(AT);
     if (AT->getElementType()->isArrayType())
       Out << 'A';
     else
       mangleQualifiers(Ty.getQualifiers(), false);
   } else {
-    mangleType(Ty, TL.getSourceRange(), QMM_Drop);
+    mangleType(Ty, SR, QMM_Drop);
     mangleQualifiers(Ty.getLocalQualifiers(), false);
   }
 }
 
 void MicrosoftCXXNameMangler::mangleMemberDataPointer(const CXXRecordDecl *RD,
                                                       const ValueDecl *VD) {
   // <member-data-pointer> ::= <integer-literal>
   //                       ::= $F <number> <number>