[clang-tools-extra] [clang-tidy] Ignore expresions in unevaluated context in bugprone-inc-dec-in-conditions (PR #85849)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL created https://github.com/llvm/llvm-project/pull/85849

Skip checking for references to variable in unevaluated context, like decltype, static_assert and so on.

Closes #85838

>From 2bd3d15a9e4a9a34bb9edb12815207093c0f3157 Mon Sep 17 00:00:00 2001
From: Piotr Zegar <me at piotrzegar.pl>
Date: Tue, 19 Mar 2024 19:09:38 +0000
Subject: [PATCH] [clang-tidy] Ignore expresions in unevaluated context in
 bugprone-inc-dec-in-conditions

Skip checking for references to variable in unevaluated context,
like decltype, static_assert and so on.

Closes #85838
---
 .../clang-tidy/bugprone/IncDecInConditionsCheck.cpp      | 7 ++++++-
 clang-tools-extra/docs/ReleaseNotes.rst                  | 4 ++++
 .../checkers/bugprone/inc-dec-in-conditions.cpp          | 9 +++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
index 16f43128d55e87..c9990cf6d10fd5 100644
--- a/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/IncDecInConditionsCheck.cpp
@@ -31,6 +31,10 @@ void IncDecInConditionsCheck::registerMatchers(MatchFinder *Finder) {
       anyOf(binaryOperator(anyOf(isComparisonOperator(), isLogicalOperator())),
             cxxOperatorCallExpr(isComparisonOperator())));
 
+  auto IsInUnevaluatedContext =
+      expr(anyOf(hasAncestor(expr(matchers::hasUnevaluatedContext())),
+                 hasAncestor(typeLoc())));
+
   Finder->addMatcher(
       expr(
           OperatorMatcher, unless(isExpansionInSystemHeader()),
@@ -47,7 +51,8 @@ void IncDecInConditionsCheck::registerMatchers(MatchFinder *Finder) {
                             hasDescendant(
                                 expr(unless(equalsBoundNode("operand")),
                                      matchers::isStatementIdenticalToBoundNode(
-                                         "operand"))
+                                         "operand"),
+                                     unless(IsInUnevaluatedContext))
                                     .bind("second")))))
                   .bind("operator"))),
       this);
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 44680f79de6f54..8803be56d4fd1a 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -132,6 +132,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/assert-side-effect>` check by detecting side
   effect from calling a method with non-const reference parameters.
 
+- Improved :doc:`bugprone-inc-dec-in-conditions
+  <clang-tidy/checks/bugprone/inc-dec-in-conditions>` check to ignore code
+  within unevaluated contexts, such as ``decltype``.
+
 - Improved :doc:`bugprone-non-zero-enum-to-bool-conversion
   <clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion>` check by
   eliminating false positives resulting from direct usage of bitwise operators
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 82af039973c3bb..a9cb27a47f35b5 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
@@ -68,3 +68,12 @@ bool doubleCheck(Container<int> x) {
   // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: decrementing and referencing a variable in a complex condition can cause unintended side-effects due to C++'s order of evaluation, consider moving the modification outside of the condition to avoid misunderstandings [bugprone-inc-dec-in-conditions]
   // CHECK-MESSAGES: :[[@LINE-2]]:31: warning: incrementing and referencing a variable in a complex condition can cause unintended side-effects due to C++'s order of evaluation, consider moving the modification outside of the condition to avoid misunderstandings [bugprone-inc-dec-in-conditions]
 }
+
+namespace PR85838 {
+  void test()
+  {
+    auto foo = 0;
+    auto bar = 0;
+    if (++foo < static_cast<decltype(foo)>(bar)) {}
+  }
+}