[libclang] Fix crash when visiting a captured VLA.

[ckandeler]

Summary

When a variable-length array is being captured in a lambda, the AST
contains two captures, the first one having a null init expression.
Visiting that one triggers an assertion, so skip it.

[ckandeler]

Fixed formatting issues.

[milianw]

this relates to https://reviews.llvm.org/D82740 too, but comes with a test which is good. personally I would place the check directly within Visit to make it more generically prevent a crash on invalid input, but that's probably a subjective design decision.

[ckandeler]

I suppose it boils down to whether the visit() function is supposed to accept null arguments or not. Since I don't know the answer to that, I added the check at the caller. From the description of the linked patch, it appears that other places are also calling the function with a null pointer, but that could just mean that these should be fixed independently. Someone with better knowledge of the code would have to make that decision.

[jkorous]

LGTM! Thanks for fixing this!

[jkorous]

@ckandeler do you have commit access or do you want me to land the patch?

[ckandeler]

In D82629#2134521, @jkorous wrote:

@ckandeler do you have commit access or do you want me to land the patch?

I do not, so it'd be great if you could do it.

clang/test/Index/evaluate-cursor.cpp

 template <typename d> class e {
   using f = d;
   static const auto g = alignof(f);
 };
 
 constexpr static int calc_val() { return 1 + 2; }
 const auto the_value = calc_val() + sizeof(char);
 
+void vlaTest() {
+  int msize = 4;
+  float arr[msize];
+  [&arr] {};
+}
+
 // 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: c-index-test -evaluate-cursor-at=%s:30:1 \
 // RUN:    -evaluate-cursor-at=%s:30:32 \
 // RUN:    -evaluate-cursor-at=%s:30:35 \
 // RUN:    -evaluate-cursor-at=%s:30:37 -std=c++11 %s | FileCheck %s -check-prefix=CHECK-EXPR
 // CHECK-EXPR: unsigned, Value: 4
 // CHECK-EXPR: Value: 3
 // CHECK-EXPR: unsigned, Value: 4
 // CHECK-EXPR: unsigned, Value: 1
+
+// RUN: c-index-test -evaluate-cursor-at=%s:35:5 \
+// RUN:    -std=c++11 %s | FileCheck -check-prefix=VLA %s
+// VLA: Not Evaluatable

clang/tools/libclang/CIndex.cpp

case VisitorJob::LambdaExprPartsKind: {
           continue;
 
         if (Visit(MakeCursorVariableRef(C->getCapturedVar(), C->getLocation(),
                                         TU)))
           return true;
       }
       // Visit init captures
       for (auto InitExpr : E->capture_inits()) {
-        if (Visit(InitExpr))
+        if (InitExpr && Visit(InitExpr))
           return true;
       }
 
       TypeLoc TL = E->getCallOperator()->getTypeSourceInfo()->getTypeLoc();
       // Visit parameters and return type, if present.
       if (FunctionTypeLoc Proto = TL.getAs<FunctionProtoTypeLoc>()) {
         if (E->hasExplicitParameters()) {
           // Visit parameters.