[clang-tidy] Ignore expresions in unevaluated context in bugprone-inc…

…-dec-in-conditions (#85849) Skip checking for references to variable in unevaluated context, like decltype, static_assert and so on. Closes #85838
llvm · Mar 24, 2024 · d4a4585 · d4a4585
1 parent 4804805
commit d4a4585
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Showing 3 changed files with 21 additions and 1 deletion.
diff --git 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()),
@@ -42,12 +46,14 @@ void IncDecInConditionsCheck::registerMatchers(MatchFinder *Finder) {
                          cxxOperatorCallExpr(
                              isPrePostOperator(),
                              hasUnaryOperand(expr().bind("operand")))),
+                   unless(IsInUnevaluatedContext),
                    hasAncestor(
                        expr(equalsBoundNode("parent"),
                             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
@@ -139,6 +139,10 @@ 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
@@ -68,3 +68,13 @@ 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)) {}
+    if (static_cast<decltype(++foo)>(bar) < foo) {}
+  }
+}