[clang-tools-extra] 187e050 - [clang-tidy] performance-unnecessary-copy-initialization: Disable structured bindings.

[Felix Berger via cfe-commits]

Author: Felix Berger
Date: 2021-07-12T09:55:27-04:00
New Revision: 187e050b33bbee1ef210c83f5595c283ba671909

URL: https://github.com/llvm/llvm-project/commit/187e050b33bbee1ef210c83f5595c283ba671909
DIFF: https://github.com/llvm/llvm-project/commit/187e050b33bbee1ef210c83f5595c283ba671909.diff

LOG: [clang-tidy] performance-unnecessary-copy-initialization: Disable structured bindings.

Structured bindings can currently trigger the check and lead to a wrong
fix. Because the DecompositionDecl itself is not used and the check does not
iterate through its the decl's bindings to verify whether the bindings' holding
vars are used this leads to the whole statement to be deleted.

To support structured bindings properly 3 cases would need to be considered.

  1. All holding vars are not used -> The statement can be deleted.
  2. All holding vars are used as const or not used -> auto can be converted to const auto&.
  3. Neither case is true -> leave unchanged.

In the check we'll have to separate the logic that determines this from the code
that produces the diagnostic and fixes and first determine which of the cases
we're dealing with before creating fixes.

Since this is a bigger refactoring we'll disable structured bindings for now to
prevent incorrect fixes.

Differential Revision: https://reviews.llvm.org/D105727

Reviewed-by: ymandel

Added: 
    

Modified: 
    clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
    clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp

Removed: 
    


################################################################################
diff  --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
index f75a3a901ecd5..f69a2079e4ba1 100644
--- a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
+++ b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
@@ -147,6 +147,7 @@ void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
     return compoundStmt(
                forEachDescendant(
                    declStmt(
+                       unless(has(decompositionDecl())),
                        has(varDecl(hasLocalStorage(),
                                    hasType(qualType(
                                        hasCanonicalType(allOf(

diff  --git a/clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
index c2b3d8f9c7395..b66a88e5cf81f 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s performance-unnecessary-copy-initialization %t
+// RUN: %check_clang_tidy -std=c++17 %s performance-unnecessary-copy-initialization %t
 
 template <typename T>
 struct Iterator {
@@ -637,3 +637,18 @@ void negativeReferenceIsInitializedOutsideOfBlock() {
     }
   };
 }
+
+void negativeStructuredBinding() {
+  // Structured bindings are not yet supported but can trigger false positives
+  // since the DecompositionDecl itself is unused and the check doesn't traverse
+  // VarDecls of the BindingDecls.
+  struct Pair {
+    ExpensiveToCopyType first;
+    ExpensiveToCopyType second;
+  };
+
+  Pair P;
+  const auto [C, D] = P;
+  C.constMethod();
+  D.constMethod();
+}