[clang-tools-extra] Add bugprone-loop-variable-copied-then-modified clang-tidy check. (PR #157213)

[Nicolas van Kempen via cfe-commits]

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@@ -0,0 +1,55 @@
+// RUN: %check_clang_tidy %s bugprone-loop-variable-copied-then-modified %t -- -- -I%S -std=c++!4 -config="{CheckOptions: {bugprone-loop-variable-copied-then-modified.IgnoreInexpensiveVariables: true}}"
+
+#include "Inputs/system-header-simulator/sim_set"
+#include "Inputs/system-header-simulator/sim_unordered_set"
+#include "Inputs/system-header-simulator/sim_map"
+#include "Inputs/system-header-simulator/sim_unordered_map"
+#include "Inputs/system-header-simulator/sim_vector"
+#include "Inputs/system-header-simulator/sim_algorithm"
+
+template <typename T>
+struct Iterator {
+  void operator++() {}
+  const T& operator*() {
+    static T* TT = new T();
+    return *TT;
+  }
+  bool operator!=(const Iterator &) { return false; }
+};
+template <typename T>
+struct View {
+  T begin() { return T(); }
+  T begin() const { return T(); }
+  T end() { return T(); }
+  T end() const { return T(); }
+};
+
+struct S {
+  int value;
+
+  S() : value(0) {};
+  S(const S &);
+  ~S();
+  S &operator=(const S &);
+  void modify() {
+    value++;
+  }
+};
+
+void NegativeOnlyCopyingInts() {
+    std::vector<int> foo;
+    foo.push_back(1);
+    foo.push_back(2);
+    foo.push_back(3);
+    for (int v : foo) {
+        v += 1;
+    }
+}
+
+void PositiveLoopVariableCopiedAndThenModfied() {
+  for (S S1 : View<Iterator<S>>()) {
+    // CHECK-MESSAGES: [[@LINE-1]]:10: warning: loop variable 'S1' is copied and then modified, which is likely a bug; you probably want to modify the underlying object and not this copy. If you *did* intend to modify this copy, please use an explicit copy inside the body of the loop
+    // CHECK-FIXES: for (const S& S1 : View<Iterator<S>>()) {
+    S1.modify();
+  }
+}
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nicovank wrote:

Newline

https://github.com/llvm/llvm-project/pull/157213