clang-tidy: not suggest cmStrCat for short appends and concats

We rely, that standard library have really effective `+=` and `+` operators
for `std::string` with any paired arguments: `std::string`, `const char *` and `char`.
So, that change just blocks `c = a + b` and `c += a` replacements,
but still replaces the `c = a + b + d` and `c += a + b` and longer (with more `+` operators).

Utilities/ClangTidyModule/StringConcatenationUseCmstrcatCheck.cxx

@@ -126,6 +126,10 @@ void StringConcatenationUseCmstrcatCheck::check(
 void StringConcatenationUseCmstrcatCheck::issueCorrection(
   ExprChain const& Chain, MatchFinder::MatchResult const& Result)
 {
+  if (Chain.second.size() < 2) {
+    return;
+  }
+
   std::vector<FixItHint> FixIts;
   CXXOperatorCallExpr const* ExprNode;
   std::vector<clang::CXXOperatorCallExpr const*>::const_iterator It =

Utilities/ClangTidyModule/Tests/cmake-string-concatenation-use-cmstrcat-fixit.cxx

@@ -14,20 +14,18 @@ std::string concat;
 // Correction needed
 void test1()
 {
-  concat = cmStrCat(a, b);
-  concat = cmStrCat(a, " and this is a string literal");
-  concat = cmStrCat(a, 'O');
-  concat = cmStrCat("This is a string literal", b);
-  concat = cmStrCat('O', a);
   concat = cmStrCat(a, " and this is a string literal", 'O', b);
 
-  concat = cmStrCat(concat, b);
+  concat = cmStrCat(concat, a, a);
-  concat = cmStrCat(concat, " and this is a string literal");
+  concat = cmStrCat(concat, " and this is a string literal", a);
-  concat = cmStrCat(concat, 'o');
+  concat = cmStrCat(concat, b, 'o', a);
   concat = cmStrCat(concat, b, " and this is a string literal ", 'o', b);
 
+  if (true)
+    concat = cmStrCat(concat, a, b);
+
   std::pair<std::string, std::string> p;
-  concat = cmStrCat(p.first, p.second);
+  concat = cmStrCat(p.first, p.second, a);
 }
 
 // No correction needed
@@ -37,4 +35,17 @@ void test2()
   a = "This is a string literal";
   a = 'X';
   cmStrCat(a, b);
+
+  concat = a + b;
+  concat = a + " and this is a string literal";
+  concat = a + 'O';
+  concat = "This is a string literal" + b;
+  concat = 'O' + a;
+  concat += b;
+
+  std::pair<std::string, std::string> p;
+  concat = p.first + p.second;
+
+  if (true)
+    concat += a;
 }

Utilities/ClangTidyModule/Tests/cmake-string-concatenation-use-cmstrcat-stdout.txt

@@ -1,124 +1,95 @@
 cmake-string-concatenation-use-cmstrcat.cxx:17:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   17 |   concat = a + b;
+   17 |   concat = a + " and this is a string literal" + 'O' + b;
-      |            ^ ~
-      |            cmStrCat( , )
-cmake-string-concatenation-use-cmstrcat.cxx:17:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:17:14: note: FIX-IT applied suggested code changes
-   17 |   concat = a + b;
-      |              ^
-cmake-string-concatenation-use-cmstrcat.cxx:17:17: note: FIX-IT applied suggested code changes
-   17 |   concat = a + b;
-      |                 ^
-cmake-string-concatenation-use-cmstrcat.cxx:18:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   18 |   concat = a + " and this is a string literal";
-      |            ^ ~
-      |            cmStrCat( ,                        )
-cmake-string-concatenation-use-cmstrcat.cxx:18:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:18:14: note: FIX-IT applied suggested code changes
-   18 |   concat = a + " and this is a string literal";
-      |              ^
-cmake-string-concatenation-use-cmstrcat.cxx:18:47: note: FIX-IT applied suggested code changes
-   18 |   concat = a + " and this is a string literal";
-      |                                               ^
-cmake-string-concatenation-use-cmstrcat.cxx:19:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   19 |   concat = a + 'O';
-      |            ^ ~
-      |            cmStrCat( , )
-cmake-string-concatenation-use-cmstrcat.cxx:19:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:19:14: note: FIX-IT applied suggested code changes
-   19 |   concat = a + 'O';
-      |              ^
-cmake-string-concatenation-use-cmstrcat.cxx:19:19: note: FIX-IT applied suggested code changes
-   19 |   concat = a + 'O';
-      |                   ^
-cmake-string-concatenation-use-cmstrcat.cxx:20:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   20 |   concat = "This is a string literal" + b;
-      |            ^                          ~
-      |            cmStrCat(                  ,  )
-cmake-string-concatenation-use-cmstrcat.cxx:20:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:20:39: note: FIX-IT applied suggested code changes
-   20 |   concat = "This is a string literal" + b;
-      |                                       ^
-cmake-string-concatenation-use-cmstrcat.cxx:20:42: note: FIX-IT applied suggested code changes
-   20 |   concat = "This is a string literal" + b;
-      |                                          ^
-cmake-string-concatenation-use-cmstrcat.cxx:21:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   21 |   concat = 'O' + a;
-      |            ^   ~
-      |            cmStrCat( , )
-cmake-string-concatenation-use-cmstrcat.cxx:21:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:21:16: note: FIX-IT applied suggested code changes
-   21 |   concat = 'O' + a;
-      |                ^
-cmake-string-concatenation-use-cmstrcat.cxx:21:19: note: FIX-IT applied suggested code changes
-   21 |   concat = 'O' + a;
-      |                   ^
-cmake-string-concatenation-use-cmstrcat.cxx:22:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   22 |   concat = a + " and this is a string literal" + 'O' + b;
       |            ^ ~                                 ~     ~
       |            cmStrCat( ,                         ,     ,  )
-cmake-string-concatenation-use-cmstrcat.cxx:22:12: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:17:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:22:14: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:17:14: note: FIX-IT applied suggested code changes
-   22 |   concat = a + " and this is a string literal" + 'O' + b;
+   17 |   concat = a + " and this is a string literal" + 'O' + b;
       |              ^
-cmake-string-concatenation-use-cmstrcat.cxx:22:48: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:17:48: note: FIX-IT applied suggested code changes
-   22 |   concat = a + " and this is a string literal" + 'O' + b;
+   17 |   concat = a + " and this is a string literal" + 'O' + b;
       |                                                ^
-cmake-string-concatenation-use-cmstrcat.cxx:22:54: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:17:54: note: FIX-IT applied suggested code changes
-   22 |   concat = a + " and this is a string literal" + 'O' + b;
+   17 |   concat = a + " and this is a string literal" + 'O' + b;
       |                                                      ^
-cmake-string-concatenation-use-cmstrcat.cxx:22:57: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:17:57: note: FIX-IT applied suggested code changes
-   22 |   concat = a + " and this is a string literal" + 'O' + b;
+   17 |   concat = a + " and this is a string literal" + 'O' + b;
       |                                                         ^
-cmake-string-concatenation-use-cmstrcat.cxx:24:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
+cmake-string-concatenation-use-cmstrcat.cxx:19:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
-   24 |   concat += b;
+   19 |   concat += a + a;
-      |          ^~
+      |          ^~   ~
-      |          = cmStrCat(concat, )
+      |          = cmStrCat(concat, , )
-cmake-string-concatenation-use-cmstrcat.cxx:24:10: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:19:10: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:24:14: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:19:15: note: FIX-IT applied suggested code changes
-   24 |   concat += b;
+   19 |   concat += a + a;
-      |              ^
+      |               ^
-cmake-string-concatenation-use-cmstrcat.cxx:25:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
+cmake-string-concatenation-use-cmstrcat.cxx:19:18: note: FIX-IT applied suggested code changes
-   25 |   concat += " and this is a string literal";
+   19 |   concat += a + a;
-      |          ^~
+      |                  ^
-      |          = cmStrCat(concat,                )
+cmake-string-concatenation-use-cmstrcat.cxx:20:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
-cmake-string-concatenation-use-cmstrcat.cxx:25:10: note: FIX-IT applied suggested code changes
+   20 |   concat += " and this is a string literal" + a;
-cmake-string-concatenation-use-cmstrcat.cxx:25:44: note: FIX-IT applied suggested code changes
+      |          ^~                                 ~
-   25 |   concat += " and this is a string literal";
+      |          = cmStrCat(concat,                 ,  )
-      |                                            ^
+cmake-string-concatenation-use-cmstrcat.cxx:20:10: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:26:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
+cmake-string-concatenation-use-cmstrcat.cxx:20:45: note: FIX-IT applied suggested code changes
-   26 |   concat += 'o';
+   20 |   concat += " and this is a string literal" + a;
-      |          ^~
+      |                                             ^
-      |          = cmStrCat(concat, )
+cmake-string-concatenation-use-cmstrcat.cxx:20:48: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:26:10: note: FIX-IT applied suggested code changes
+   20 |   concat += " and this is a string literal" + a;
-cmake-string-concatenation-use-cmstrcat.cxx:26:16: note: FIX-IT applied suggested code changes
+      |                                                ^
-   26 |   concat += 'o';
+cmake-string-concatenation-use-cmstrcat.cxx:21:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
-      |                ^
+   21 |   concat += b + 'o' + a;
-cmake-string-concatenation-use-cmstrcat.cxx:27:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
+      |          ^~   ~     ~
-   27 |   concat += b + " and this is a string literal " + 'o' + b;
+      |          = cmStrCat(concat, , , )
+cmake-string-concatenation-use-cmstrcat.cxx:21:10: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:21:15: note: FIX-IT applied suggested code changes
+   21 |   concat += b + 'o' + a;
+      |               ^
+cmake-string-concatenation-use-cmstrcat.cxx:21:21: note: FIX-IT applied suggested code changes
+   21 |   concat += b + 'o' + a;
+      |                     ^
+cmake-string-concatenation-use-cmstrcat.cxx:21:24: note: FIX-IT applied suggested code changes
+   21 |   concat += b + 'o' + a;
+      |                        ^
+cmake-string-concatenation-use-cmstrcat.cxx:22:10: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
+   22 |   concat += b + " and this is a string literal " + 'o' + b;
       |          ^~   ~                                  ~     ~
       |          = cmStrCat(concat, ,                    ,     ,  )
-cmake-string-concatenation-use-cmstrcat.cxx:27:10: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:22:10: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:27:15: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:22:15: note: FIX-IT applied suggested code changes
-   27 |   concat += b + " and this is a string literal " + 'o' + b;
+   22 |   concat += b + " and this is a string literal " + 'o' + b;
       |               ^
-cmake-string-concatenation-use-cmstrcat.cxx:27:50: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:22:50: note: FIX-IT applied suggested code changes
-   27 |   concat += b + " and this is a string literal " + 'o' + b;
+   22 |   concat += b + " and this is a string literal " + 'o' + b;
       |                                                  ^
-cmake-string-concatenation-use-cmstrcat.cxx:27:56: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:22:56: note: FIX-IT applied suggested code changes
-   27 |   concat += b + " and this is a string literal " + 'o' + b;
+   22 |   concat += b + " and this is a string literal " + 'o' + b;
       |                                                        ^
-cmake-string-concatenation-use-cmstrcat.cxx:27:59: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:22:59: note: FIX-IT applied suggested code changes
-   27 |   concat += b + " and this is a string literal " + 'o' + b;
+   22 |   concat += b + " and this is a string literal " + 'o' + b;
       |                                                           ^
-cmake-string-concatenation-use-cmstrcat.cxx:30:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
+cmake-string-concatenation-use-cmstrcat.cxx:25:12: warning: use cmStrCat() instead of string append [cmake-string-concatenation-use-cmstrcat]
-   30 |   concat = p.first + p.second;
+   25 |     concat += a + b;
-      |            ^       ~
+      |            ^~   ~
-      |            cmStrCat( ,       )
+      |            = cmStrCat(concat, , )
-cmake-string-concatenation-use-cmstrcat.cxx:30:12: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:25:12: note: FIX-IT applied suggested code changes
-cmake-string-concatenation-use-cmstrcat.cxx:30:20: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:25:17: note: FIX-IT applied suggested code changes
-   30 |   concat = p.first + p.second;
+   25 |     concat += a + b;
+      |                 ^
+cmake-string-concatenation-use-cmstrcat.cxx:25:20: note: FIX-IT applied suggested code changes
+   25 |     concat += a + b;
       |                    ^
-cmake-string-concatenation-use-cmstrcat.cxx:30:30: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:28:12: warning: use cmStrCat() instead of string concatenation [cmake-string-concatenation-use-cmstrcat]
-   30 |   concat = p.first + p.second;
+   28 |   concat = p.first + p.second + a;
-      |                              ^
+      |            ^       ~          ~
+      |            cmStrCat( ,        ,  )
+cmake-string-concatenation-use-cmstrcat.cxx:28:12: note: FIX-IT applied suggested code changes
+cmake-string-concatenation-use-cmstrcat.cxx:28:20: note: FIX-IT applied suggested code changes
+   28 |   concat = p.first + p.second + a;
+      |                    ^
+cmake-string-concatenation-use-cmstrcat.cxx:28:31: note: FIX-IT applied suggested code changes
+   28 |   concat = p.first + p.second + a;
+      |                               ^
+cmake-string-concatenation-use-cmstrcat.cxx:28:34: note: FIX-IT applied suggested code changes
+   28 |   concat = p.first + p.second + a;
+      |                                  ^

Utilities/ClangTidyModule/Tests/cmake-string-concatenation-use-cmstrcat.cxx

@@ -14,20 +14,18 @@ std::string concat;
 // Correction needed
 void test1()
 {
-  concat = a + b;
-  concat = a + " and this is a string literal";
-  concat = a + 'O';
-  concat = "This is a string literal" + b;
-  concat = 'O' + a;
   concat = a + " and this is a string literal" + 'O' + b;
 
-  concat += b;
+  concat += a + a;
-  concat += " and this is a string literal";
+  concat += " and this is a string literal" + a;
-  concat += 'o';
+  concat += b + 'o' + a;
   concat += b + " and this is a string literal " + 'o' + b;
 
+  if (true)
+    concat += a + b;
+
   std::pair<std::string, std::string> p;
-  concat = p.first + p.second;
+  concat = p.first + p.second + a;
 }
 
 // No correction needed
@@ -37,4 +35,17 @@ void test2()
   a = "This is a string literal";
   a = 'X';
   cmStrCat(a, b);
+
+  concat = a + b;
+  concat = a + " and this is a string literal";
+  concat = a + 'O';
+  concat = "This is a string literal" + b;
+  concat = 'O' + a;
+  concat += b;
+
+  std::pair<std::string, std::string> p;
+  concat = p.first + p.second;
+
+  if (true)
+    concat += a;
 }