Bug 1475882 - clang-tidy: Enable misc-string-constructor check. r=andi

Finds string constructors that are suspicious and probably errors. There are currently no misc-string-constructor warnings in mozilla-central!

https://clang.llvm.org/extra/clang-tidy/checks/bugprone-string-constructor.html

MozReview-Commit-ID: LyJt6wqOhg9

--HG--
extra : source : 0b36b6b1b7931adec5846086a52080edb3ec5e7d
extra : histedit_source : 30249980b219d4813fc5503c87e84265ad354e2f

tools/clang-tidy/config.yaml

@@ -54,6 +54,8 @@ clang_checkers:
     publish: !!bool yes
   - name: misc-macro-repeated-side-effects
     publish: !!bool yes
+  - name: misc-string-constructor
+    publish: !!bool yes
   - name: misc-suspicious-missing-comma
     publish: !!bool yes
   - name: misc-suspicious-semicolon

tools/clang-tidy/test/misc-string-constructor.cpp

@@ -0,0 +1,17 @@
+// https://clang.llvm.org/extra/clang-tidy/checks/bugprone-string-constructor.html
+
+#include "structures.h"
+
+void test()
+{
+  // A common mistake is to swap parameters to the ‘fill’ string-constructor.
+  std::string str('x', 50); // should be str(50, 'x')
+
+  // Calling the string-literal constructor with a length bigger than the
+  // literal is suspicious and adds extra random characters to the string.
+  std::string("test", 200);   // Will include random characters after "test".
+
+  // Creating an empty string from constructors with parameters is considered
+  // suspicious. The programmer should use the empty constructor instead.
+  std::string("test", 0);   // Creation of an empty string.
+}

tools/clang-tidy/test/misc-string-constructor.json

@@ -0,0 +1 @@
+"[[\"warning\", \"string constructor parameters are probably swapped; expecting string(count, character)\", \"misc-string-constructor\"], [\"warning\", \"length is bigger then string literal size\", \"misc-string-constructor\"], [\"warning\", \"constructor creating an empty string\", \"misc-string-constructor\"]]"

tools/clang-tidy/test/structures.h

@@ -37,7 +37,9 @@ class basic_string {
 public:
   typedef basic_string<T> _Type;
   basic_string() {}
-   basic_string(const T *p);
+  basic_string(const T *p);
+  basic_string(const T *p, size_t count);
+  basic_string(size_t count, char ch);
   ~basic_string() {}
   size_t size() const;
   bool empty() const;