[clang-tools-extra] [clang-tidy] Fix `modernize-use-scoped-lock` crash on malformed code (PR #165127)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-tidy

Author: Victor Chernyakin (localspook)

<details>
<summary>Changes</summary>

This code:

```cpp
void f() {
  std::lock_guard&lt;std::mutex&gt; dont_crash {some_nonexistant_variable};
}
```

Generates an AST like this:

```txt
TranslationUnitDecl
`-FunctionDecl &lt;line:3:1, line:5:1&gt; line:3:6 f 'void ()'
  `-CompoundStmt &lt;col:10, line:5:1&gt;
    `-DeclStmt &lt;line:4:3, col:69&gt;
      `-VarDecl &lt;col:3, col:31&gt; col:31 dont_crash 
'std::lock_guard&lt;std::mutex&gt;' destroyed
```

Where the `VarDecl` has no initializer. The check doesn't expect this and 
crashes.

---
Full diff: https://github.com/llvm/llvm-project/pull/165127.diff


3 Files Affected:

- (modified) clang-tools-extra/clang-tidy/modernize/UseScopedLockCheck.cpp 
(+2-1) 
- (modified) clang-tools-extra/docs/ReleaseNotes.rst (+5) 
- (added) 
clang-tools-extra/test/clang-tidy/checkers/modernize/use-scoped-lock-no-crash.cpp
 (+9) 


``````````diff
diff --git a/clang-tools-extra/clang-tidy/modernize/UseScopedLockCheck.cpp 
b/clang-tools-extra/clang-tidy/modernize/UseScopedLockCheck.cpp
index aa1ee6db8917a..5c03c1a3aae9e 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseScopedLockCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseScopedLockCheck.cpp
@@ -217,7 +217,8 @@ void UseScopedLockCheck::diagOnSingleLock(
 
   // Create Fix-its only if we can find the constructor call to properly handle
   // 'std::lock_guard l(m, std::adopt_lock)' case.
-  const auto *CtorCall = dyn_cast<CXXConstructExpr>(LockGuard->getInit());
+  const auto *CtorCall =
+      dyn_cast_if_present<CXXConstructExpr>(LockGuard->getInit());
   if (!CtorCall)
     return;
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst 
b/clang-tools-extra/docs/ReleaseNotes.rst
index 33cc401bcb78f..d3e70f11ffaf1 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -364,6 +364,11 @@ Changes in existing checks
   on Windows when the check was enabled with a 32-bit :program:`clang-tidy`
   binary.
 
+- Improved :doc:`modernize-use-scoped-lock
+  <clang-tidy/checks/modernize/use-scoped-lock>` check by fixing a crash
+  on malformed code (common when using :program:`clang-tidy` through
+  :program:`clangd``).
+
 - Improved :doc:`modernize-use-std-format
   <clang-tidy/checks/modernize/use-std-format>` check to correctly match
   when the format string is converted to a different type by an implicit
diff --git 
a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-scoped-lock-no-crash.cpp
 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-scoped-lock-no-crash.cpp
new file mode 100644
index 0000000000000..587dbe2707873
--- /dev/null
+++ 
b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-scoped-lock-no-crash.cpp
@@ -0,0 +1,9 @@
+// RUN: %check_clang_tidy -std=c++17-or-later -expect-clang-tidy-error %s 
modernize-use-scoped-lock %t -- -- -isystem %clang_tidy_headers
+
+#include <mutex>
+
+void f() {
+  std::lock_guard<std::mutex> dont_crash {some_nonexistant_variable};
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use 'std::scoped_lock' instead 
of 'std::lock_guard' [modernize-use-scoped-lock]
+  // CHECK-MESSAGES: :[[@LINE-2]]:43: error: use of undeclared identifier 
'some_nonexistant_variable' [clang-diagnostic-error]
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/165127
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