[ASTMatchers] fix captureVars assertion failure on capturesVariables (#76619)

Matcher `capturesVar` should check for `capturesVariables()` before
calling `getCaptureVar()` since it asserts this `LambdaCapture` does
capture a variable.

Fixes #76425

Author: danix800

clang/docs/ReleaseNotes.rst

@@ -633,6 +633,7 @@ AST Matchers
 - Add ``isExplicitObjectMemberFunction``.
 - Fixed ``forEachArgumentWithParam`` and ``forEachArgumentWithParamType`` to
   not skip the explicit object parameter for operator calls.
+- Fixed captureVars assertion failure if not capturesVariables. (#GH76425)
 
 clang-format
 ------------

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -4961,6 +4961,8 @@ AST_MATCHER_P(LambdaExpr, hasAnyCapture, internal::Matcher<LambdaCapture>,
 /// capturesVar(hasName("x")) matches `x` and `x = 1`.
 AST_MATCHER_P(LambdaCapture, capturesVar, internal::Matcher<ValueDecl>,
               InnerMatcher) {
+  if (!Node.capturesVariable())
+    return false;
   auto *capturedVar = Node.getCapturedVar();
   return capturedVar && InnerMatcher.matches(*capturedVar, Finder, Builder);
 }

clang/unittests/ASTMatchers/ASTMatchersNodeTest.cpp

@@ -2321,6 +2321,8 @@ TEST_P(ASTMatchersTest, LambdaCaptureTest_BindsToCaptureOfVarDecl) {
       matches("int main() { int cc; auto f = [=](){ return cc; }; }", matcher));
   EXPECT_TRUE(
       matches("int main() { int cc; auto f = [&](){ return cc; }; }", matcher));
+  EXPECT_TRUE(matches(
+      "void f(int a) { int cc[a]; auto f = [&](){ return cc;}; }", matcher));
 }
 
 TEST_P(ASTMatchersTest, LambdaCaptureTest_BindsToCaptureWithInitializer) {