[clang-tidy] Add readability-avoid-default-lambda-capture

clang-tools-extra/clang-tidy/readability/AvoidDefaultLambdaCaptureCheck.cpp

@@ -44,16 +44,19 @@ void AvoidDefaultLambdaCaptureCheck::check(
   if (DefaultCaptureLoc.isInvalid())
     return;
 
-  auto Diag = diag(DefaultCaptureLoc,
-                   "lambda default captures are discouraged; "
-                   "prefer to capture specific variables explicitly");
-
   std::vector<std::string> ImplicitCaptures;
-
   for (const auto &Capture : Lambda->implicit_captures()) {
+    // It is impossible to explicitly capture a VLA in C++, since VLAs don't
+    // exist in ISO C++ and so the syntax was never created to capture them.
+    if (Capture.getCaptureKind() == LCK_VLAType)
+      return;
     ImplicitCaptures.push_back(generateCaptureText(Capture));
   }
 
+  auto Diag = diag(DefaultCaptureLoc,
+                   "lambda default captures are discouraged; "
+                   "prefer to capture specific variables explicitly");
+
   // For template-dependent lambdas, the list of captures hasn't been created
   // yet, so the list of implicit captures is empty.
   if (ImplicitCaptures.empty() && Lambda->isGenericLambda())

clang-tools-extra/docs/clang-tidy/checks/readability/avoid-default-lambda-capture.rst

@@ -13,6 +13,10 @@ Coding guidelines that recommend against defaulted lambda captures include:
 
 * Item 31 of Effective Modern C++ by Scott Meyers
 
+This check does not lint for variable-length array (VLA) captures. VLAs are not
+ISO C++, and it is impossible to explicitly capture them as the syntax does not
+exist.
+
 Example
 -------
 

clang-tools-extra/test/clang-tidy/checkers/readability/avoid-default-lambda-capture.cpp

@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s readability-avoid-default-lambda-capture %t
+// RUN: %check_clang_tidy %s readability-avoid-default-lambda-capture %t -- -- -Wno-vla-extension
 
 void test_default_captures() {
   int value = 42;
@@ -129,3 +129,15 @@ void test_init_captures() {
   (void)y1;
   (void)y2;
 }
+
+void test_vla_no_crash() {
+  // VLAs create implicit VLA bound captures that cannot be written explicitly.
+  // No warning should be issued.
+  int n = 5;
+  int vla[n];
+  for (int i = 0; i < n; ++i) {
+    vla[i] = i * 10;
+  }
+
+  auto lambda = [&]() { return vla[0]; };
+}