From 71263dc615cd6ece304e4326485336691c2ddc26 Mon Sep 17 00:00:00 2001
From: Baranov Victor <bar.victor.2002@gmail.com>
Date: Sun, 29 Mar 2026 09:11:28 +0300
Subject: [PATCH] [clang-tidy] Fix bugprone-inc-dec-in-conditions FP with
 lambda condition (#189145)

Fixes https://github.com/llvm/llvm-project/issues/163913.
---
 .../bugprone/IncDecInConditionsCheck.cpp      |  5 ++-
 clang-tools-extra/docs/ReleaseNotes.rst       |  5 +++
 .../bugprone/inc-dec-in-conditions.cpp        | 44 +++++++++++++++++++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
index 9f723d52f60e..bdb91b1ed0f4 100644
--- a/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
@@ -39,6 +39,9 @@ void IncDecInConditionsCheck::registerMatchers(MatchFinder *Finder) {
       expr(anyOf(hasAncestor(expr(matchers::hasUnevaluatedContext())),
                  hasAncestor(typeLoc())));
 
+  auto IsInLambda =
+      hasAncestor(lambdaExpr(hasAncestor(expr(equalsBoundNode("parent")))));
+
   Finder->addMatcher(
       expr(
           OperatorMatcher, unless(hasAncestor(OperatorMatcher)),
@@ -50,7 +53,7 @@ void IncDecInConditionsCheck::registerMatchers(MatchFinder *Finder) {
                          cxxOperatorCallExpr(
                              isPrePostOperator(),
                              hasUnaryOperand(expr().bind("operand")))),
-                   unless(IsInUnevaluatedContext),
+                   unless(IsInUnevaluatedContext), unless(IsInLambda),
                    hasAncestor(
                        expr(equalsBoundNode("parent"),
                             hasDescendant(
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 637edaece2a9..eb735e6e62ee 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -219,6 +219,11 @@ Changes in existing checks
   loss in overloads with transparent standard functors (e.g. ``std::plus<>``)
   for ``std::accumulate``, ``std::reduce``, and ``std::inner_product``.
 
+- Improved :doc:`bugprone-inc-dec-in-conditions
+  <clang-tidy/checks/bugprone/inc-dec-in-conditions>` check by fixing a false
+  positive when increment/decrement operators appear inside lambda bodies that
+  are part of a condition expression.
+
 - Improved :doc:`bugprone-macro-parentheses
   <clang-tidy/checks/bugprone/macro-parentheses>` check by printing the macro
   definition in the warning message if the macro is defined on command line.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/inc-dec-in-conditions.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/inc-dec-in-conditions.cpp
index 91de013138f0..82a36f1dc3e0 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/inc-dec-in-conditions.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/inc-dec-in-conditions.cpp
@@ -78,3 +78,47 @@ namespace PR85838 {
     if (static_cast<decltype(++foo)>(bar) < foo) {}
   }
 }
+
+namespace GH163913 {
+  void lambdaWithIncrement(int size) {
+    if ([](int n) {
+        ++n;
+        return n;
+    }(size) < 42) {}
+  }
+
+  void lambdaWithDecrement(int size) {
+    if ([](int n) {
+        --n;
+        return n;
+    }(size) < 42) {}
+  }
+
+  template <typename Func>
+  auto eval(Func&& fn) -> decltype(fn()) {
+    return fn();
+  }
+
+  void lambdaWithForLoop(int size) {
+    if (eval([&] {
+        int result = 0;
+        for (int i = 0; i < size; i++) {
+            result += i;
+        }
+        return result;
+    }) < 42) {}
+  }
+
+  void outsideLambda(int size) {
+    if ([](int n) {
+        --n;
+        return n;
+    }(size) < ++size) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: incrementing and referencing a variable in a complex condition
+    if (++size > [](int n) {
+        --n;
+        return n;
+    }(size)) {}
+    // CHECK-MESSAGES: :[[@LINE-4]]:9: warning: incrementing and referencing a variable in a complex condition
+  }
+}