[libclang] Fix hang in release / assertion in debug when evaluating value-dependent types.

[emilio]

Summary

Expression evaluator doesn't work in value-dependent types, so ensure that the
precondition it asserts holds.

This fixes https://bugs.llvm.org/show_bug.cgi?id=42532.

[Anastasia]

LGTM! Thanks!

[emilio]

Thanks for the review as always @Anastasia ^.^

clang/test/Index/evaluate-cursor.cpp

 }
 
 unsigned long long foo_int = 1ull << 60;
 
 unsigned long long HUGE = 1ull << 63;
 
 long long HUGE_NEG = -(1ll << 35);
 
+template <typename d> class e {
+  using f = d;
+  static const auto g = alignof(f);
+};
+
 // RUN: c-index-test -evaluate-cursor-at=%s:4:7 \
 // RUN:    -evaluate-cursor-at=%s:8:7 \
 // RUN:    -evaluate-cursor-at=%s:8:11 -std=c++11 %s | FileCheck %s
 // CHECK: Value: 10
 // CHECK: Value: 11
 // CHECK: Value: 11
 
 // RUN: c-index-test -get-macro-info-cursor-at=%s:11:9 \
 // RUN:    -get-macro-info-cursor-at=%s:14:11 \
 // RUN:    -get-macro-info-cursor-at=%s:15:11 -std=c++11 %s | FileCheck -check-prefix=CHECK-MACRO %s
 // CHECK-MACRO: [function macro]
 // CHECK-MACRO: [function macro]
 // CHECK-MACRO: [builtin macro]
 
 // RUN: c-index-test -evaluate-cursor-at=%s:18:20 \
 // RUN:    -evaluate-cursor-at=%s:20:20 \
 // RUN:    -evaluate-cursor-at=%s:22:11 \
 // RUN:    -std=c++11 %s | FileCheck -check-prefix=CHECK-LONG %s
 // CHECK-LONG: unsigned, Value: 1152921504606846976
 // CHECK-LONG: unsigned, Value: 9223372036854775808
 // CHECK-LONG: Value: -34359738368
+
+// RUN: c-index-test -evaluate-cursor-at=%s:18:20 \
+// RUN:    -evaluate-cursor-at=%s:20:20 \
+// RUN:    -evaluate-cursor-at=%s:26:21 \
+// RUN:    -std=c++11 %s | FileCheck -check-prefix=CHECK-DOES-NOT-CRASH %s
+// CHECK-DOES-NOT-CRASH: Not Evaluatable

clang/tools/libclang/CIndex.cpp

 
 static const ExprEvalResult* evaluateExpr(Expr *expr, CXCursor C) {
   Expr::EvalResult ER;
   ASTContext &ctx = getCursorContext(C);
   if (!expr)
     return nullptr;
 
   expr = expr->IgnoreParens();
+  if (expr->isValueDependent())
+    return nullptr;
   if (!expr->EvaluateAsRValue(ER, ctx))
     return nullptr;
 
   QualType rettype;
   CallExpr *callExpr;
   auto result = llvm::make_unique<ExprEvalResult>();
   result->EvalType = CXEval_UnExposed;
   result->IsUnsignedInt = false;