[clang-tools-extra] 8c3ef3b - [clang-tidy] Fix assignment-in-if-condition false positive in statement expressions (#231704)

[via cfe-commits]

Author: mark-zilber
Date: 2026-10-18T21:20:17+03:00
New Revision: 8c3ef3bef883424fa714b307f8b52c0685496008

URL: https://github.com/llvm/llvm-project/commit/8c3ef3bef883424fa714b307f8b52c0685496008
DIFF: https://github.com/llvm/llvm-project/commit/8c3ef3bef883424fa714b307f8b52c0685496008.diff

LOG: [clang-tidy] Fix assignment-in-if-condition false positive in statement expressions (#231704)

The check traversed into GNU statement expressions and diagnosed
assignments in separate statements inside them, e.g. `({ ...; r = ...;
r; })`.

Now the check only looks at the last statement of a GNU statement
expression, skipping any labels or attributes on it. An assignment that
is itself the value is still diagnosed.

Fixes #210638

Added: 
    

Modified: 
    clang-tools-extra/clang-tidy/bugprone/AssignmentInIfConditionCheck.cpp
    clang-tools-extra/docs/ReleaseNotes.md
    clang-tools-extra/test/clang-tidy/checkers/bugprone/assignment-in-if-condition.cpp

Removed: 
    


################################################################################
diff  --git a/clang-tools-extra/clang-tidy/bugprone/AssignmentInIfConditionCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/AssignmentInIfConditionCheck.cpp
index d5d8a29d969693..ac5ab07fd3e061 100644
--- a/clang-tools-extra/clang-tidy/bugprone/AssignmentInIfConditionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/AssignmentInIfConditionCheck.cpp
@@ -45,6 +45,16 @@ void AssignmentInIfConditionCheck::check(
           return true;
         }
 
+        // Only traverse the result expression of a statement expression,
+        // looking through labels and attributes on the last statement.
+        bool TraverseStmtExpr(StmtExpr *SE,
+                              DataRecursionQueue *Queue = nullptr) {
+          if (auto *Last =
+                  dyn_cast_if_present<ValueStmt>(SE->getSubStmt()->body_back()))
+            return TraverseStmt(Last->getExprStmt(), Queue);
+          return true;
+        }
+
         bool VisitBinaryOperator(BinaryOperator *BO) {
           if (BO->isAssignmentOp())
             Check.report(BO);

diff  --git a/clang-tools-extra/docs/ReleaseNotes.md b/clang-tools-extra/docs/ReleaseNotes.md
index fdab8b19b63a8b..b48662c1934423 100644
--- a/clang-tools-extra/docs/ReleaseNotes.md
+++ b/clang-tools-extra/docs/ReleaseNotes.md
@@ -180,6 +180,11 @@ infrastructure are described first, followed by tool-specific sections.
 
 #### Changes in existing checks
 
+- Improved {doc}`bugprone-assignment-in-if-condition
+  <clang-tidy/checks/bugprone/assignment-in-if-condition>` check by ignoring
+  assignments inside GNU statement expressions unless they form the value of
+  the statement expression.
+
 - Improved {doc}`bugprone-easily-swappable-parameters
   <clang-tidy/checks/bugprone/easily-swappable-parameters>` check by no longer
   emitting empty notes for type aliases when {option}`ModelImplicitConversions`

diff  --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/assignment-in-if-condition.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/assignment-in-if-condition.cpp
index ad0d360d99fefc..fb3d7adaed3b13 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/assignment-in-if-condition.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/assignment-in-if-condition.cpp
@@ -80,6 +80,59 @@ void f5(int arg) {
   v = f;
 }
 
+void f6(int arg) {
+  int x;
+  if (({ x = 5; }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f7(int arg) {
+  if (({ int r; r = arg; (r = 1); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:29: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f8(int arg) {
+  if (({ label: arg = 1; }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:21: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+int get_value();
+
+void f9(int arg) {
+  if (({ [[clang::nomerge]] arg = get_value(); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:33: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f10(int x, int y) {
+  if (({ x = 1; ({ y = 2; }); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:22: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f11(int x) {
+  if (({ ({ x = 1; }); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f12(int arg) {
+  BrokenOperator bo1, bo2;
+  if (({ bo1 = arg; ({ bo2 = arg; }); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:28: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
+void f13(int arg) {
+  BrokenOperator bo;
+  if (({ ({ bo = arg; }); }))
+  // CHECK-MESSAGES: :[[@LINE-1]]:16: warning: an assignment within an 'if' condition is bug-prone [bugprone-assignment-in-if-condition]
+    return;
+}
+
 // Tests that shouldn't trigger warnings.
 void awesome_f2(int arg) {
   int f = 3;
@@ -102,6 +155,34 @@ void awesome_f4(int arg) {
   }
 }
 
+#define STMT_EXPR_MACRO(arg)                                                   \
+  ({                                                                           \
+    bool R;                                                                    \
+    R = (arg) != 1;                                                            \
+    R;                                                                         \
+  })
+
+void awesome_f5(int arg) {
+  if (STMT_EXPR_MACRO(arg))
+    return;
+}
+
+void awesome_f6(int arg) {
+  if (({ int r; r = arg; r; }))
+    return;
+}
+
+void awesome_f7(int x, int y) {
+  if (({ x = 1; ({ y = 2; y; }); }))
+    return;
+}
+
+void awesome_f8(int arg) {
+  BrokenOperator bo;
+  if (({ bo = arg; ({ bo = 2; bo.d; }); }))
+    return;
+}
+
 template <typename Func> bool exec(Func F) { return F(); }
 
 void lambda_if() {