[clang-tools-extra] [clang-tidy] Improve `bugprone-exception-escape`'s handling of lambdas (PR #160592)

[Victor Chernyakin via cfe-commits]

https://github.com/localspook created https://github.com/llvm/llvm-project/pull/160592

Fixes #132605.

>From d9d55b575b9f79fca04363409bbbe35c7312a21c Mon Sep 17 00:00:00 2001
From: Victor Chernyakin <chernyakin.victor.j at outlook.com>
Date: Wed, 24 Sep 2025 12:43:55 -0700
Subject: [PATCH] [clang-tidy] Improve `bugprone-exception-escape`'s handling
 of lambdas

---
 .../clang-tidy/utils/ExceptionAnalyzer.cpp    |  5 +++
 clang-tools-extra/docs/ReleaseNotes.rst       |  5 +++
 .../checkers/bugprone/exception-escape.cpp    | 38 +++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp b/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
index bdde7249d2796..fd4320eb8144b 100644
--- a/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
+++ b/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
@@ -595,6 +595,11 @@ ExceptionAnalyzer::throwsException(const Stmt *St,
         Results.merge(DestructorExcs);
       }
     }
+  } else if (const auto *Lambda = dyn_cast<LambdaExpr>(St)) {
+    for (const Stmt *Init : Lambda->capture_inits()) {
+      ExceptionInfo Excs = throwsException(Init, Caught, CallStack);
+      Results.merge(Excs);
+    }
   } else {
     for (const Stmt *Child : St->children()) {
       ExceptionInfo Excs = throwsException(Child, Caught, CallStack);
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 7cdff86beeec6..63ea45cb39270 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -210,6 +210,11 @@ Changes in existing checks
   correcting a spelling mistake on its option
   ``NamePrefixSuffixSilenceDissimilarityTreshold``.
 
+- Improved :doc:`bugprone-exception-escape
+  <clang-tidy/checks/bugprone/exception-escape>` check's handling of lambdas:
+  exceptions from captures are now diagnosed, exceptions in the bodies of
+  lambdas that aren't actually invoked are not.
+
 - Improved :doc:`bugprone-infinite-loop
   <clang-tidy/checks/bugprone/infinite-loop>` check by adding detection for
   variables introduced by structured bindings.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
index b10bd1d482867..da200cd6de8df 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
@@ -894,3 +894,41 @@ void pointer_exception_can_not_escape_with_void_handler() noexcept {
   } catch (void *) {
   }
 }
+
+void throw_in_uninvoked_lambda() noexcept {
+  [] { throw 42; };
+}
+
+struct copy_constructor_throws {
+  copy_constructor_throws(const copy_constructor_throws&) { throw 42; }
+};
+
+void throw_in_lambda_default_by_value_capture(const copy_constructor_throws& a) noexcept {
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: an exception may be thrown in function 'throw_in_lambda_default_by_value_capture' which should not throw exceptions
+  [=] { a; };
+  // CHECK-MESSAGES: :[[@LINE-6]]:61: note: frame #0: unhandled exception of type 'int' may be thrown in function 'copy_constructor_throws' here
+  // CHECK-MESSAGES: :[[@LINE-2]]:4: note: frame #1: function 'throw_in_lambda_default_by_value_capture' calls function 'copy_constructor_throws' here
+}
+
+void throw_in_lambda_explicit_by_value_capture(const copy_constructor_throws& a) noexcept {
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: an exception may be thrown in function 'throw_in_lambda_explicit_by_value_capture' which should not throw exceptions
+  [a] {};
+  // CHECK-MESSAGES: :[[@LINE-13]]:61: note: frame #0: unhandled exception of type 'int' may be thrown in function 'copy_constructor_throws' here
+  // CHECK-MESSAGES: :[[@LINE-2]]:4: note: frame #1: function 'throw_in_lambda_explicit_by_value_capture' calls function 'copy_constructor_throws' here
+}
+
+void no_throw_in_lambda_by_reference_capture(const copy_constructor_throws& a) noexcept {
+  [&] { a; };
+  [&a] {};
+}
+
+void throw_in_uninvoked_lambda() noexcept {
+  [] { throw 42; };
+}
+
+void throw_in_lambda() noexcept {
+  // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: an exception may be thrown in function 'throw_in_lambda' which should not throw exceptions
+  [] { throw 42; }();
+  // CHECK-MESSAGES: :[[@LINE-1]]:8: note: frame #0: unhandled exception of type 'int' may be thrown in function 'operator()' here
+  // CHECK-MESSAGES: :[[@LINE-2]]:19: note: frame #1: function 'throw_in_lambda' calls function 'operator()' here
+}