[clang-tidy] Don't treat invalid branches as identical

The clang-tidy check bugprone-branch-clone has a false positive if some
symbols are undefined. This patch silences the warning when the two
sides of a branch are invalid.

Fixes #56057

Differential Revision: https://reviews.llvm.org/D128402

clang-tools-extra/clang-tidy/bugprone/BranchCloneCheck.cpp

@@ -19,6 +19,17 @@ using namespace clang::ast_matchers;
 /// Returns true when the statements are Type I clones of each other.
 static bool areStatementsIdentical(const Stmt *LHS, const Stmt *RHS,
                                    const ASTContext &Context) {
+  if (isa<Expr>(LHS) && isa<Expr>(RHS)) {
+    // If we have errors in expressions, we will be unable
+    // to accurately profile and compute hashes for each
+    // of the left and right statements.
+    const auto *LHSExpr = llvm::cast<Expr>(LHS);
+    const auto *RHSExpr = llvm::cast<Expr>(RHS);
+    if (LHSExpr->containsErrors() && RHSExpr->containsErrors()) {
+      return false;
+    }
+  }
+
   llvm::FoldingSetNodeID DataLHS, DataRHS;
   LHS->Profile(DataLHS, Context, false);
   RHS->Profile(DataRHS, Context, false);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -158,6 +158,10 @@ Changes in existing checks
 - Fixed nonsensical suggestion of :doc:`altera-struct-pack-align
   <clang-tidy/checks/altera/struct-pack-align>` check for empty structs.
 
+- Fixed a false positive in :doc:`bugprone-branch-clone
+  <clang-tidy/checks/bugprone/branch-clone>` when the branches
+  involve unknown expressions.
+
 - Fixed some false positives in :doc:`bugprone-infinite-loop
   <clang-tidy/checks/bugprone/infinite-loop>` involving dependent expressions.
 

clang-tools-extra/test/clang-tidy/checkers/bugprone/branch-clone-unknown-expr.cpp

@@ -0,0 +1,9 @@
+// RUN: %check_clang_tidy -expect-clang-tidy-error %s bugprone-branch-clone %t
+
+int test_unknown_expression() {
+  if (unknown_expression_1) {        // CHECK-MESSAGES: :[[@LINE]]:7: error: use of undeclared identifier 'unknown_expression_1' [clang-diagnostic-error]
+    function1(unknown_expression_2); // CHECK-MESSAGES: :[[@LINE]]:15: error: use of undeclared identifier 'unknown_expression_2' [clang-diagnostic-error]
+  } else {
+    function2(unknown_expression_3); // CHECK-MESSAGES: :[[@LINE]]:15: error: use of undeclared identifier 'unknown_expression_3' [clang-diagnostic-error]
+  }
+}