[clang-tidy] Enhance misc-suspicious-string-compare to move down false-positives.

Summary:
The checker was noisy when running over llvm code base.
This patch is impriving the way string-compare functions are matched.

1) By default, do not report !strcmp(...) unless it's activate by the user,
2) Only match suspicious expression over a subset of expression (binary operator),
3) Added matching of macro wrapper used with clang on linux.

See bug: 27465.

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D19497

llvm-svn: 267570

1 files changed, 38 insertions, 0 deletions

diff --git a/clang-tools-extra/test/clang-tidy/misc-suspicious-string-compare.cpp b/clang-tools-extra/test/clang-tidy/misc-suspicious-string-compare.cpp
index 8bdb897cbb1..4c51676ded3 100644
--- a/clang-tools-extra/test/clang-tidy/misc-suspicious-string-compare.cpp
+++ b/clang-tools-extra/test/clang-tidy/misc-suspicious-string-compare.cpp
@@ -15,6 +15,8 @@ static const unsigned char U[] = "abc";
 static const unsigned char V[] = "xyz";
 static const wchar_t W[] = L"abc";
 
+int strlen(const char *);
+
 int memcmp(const void *, const void *, size);
 int wmemcmp(const wchar_t *, const wchar_t *, size);
 int memicmp(const void *, const void *, size);
@@ -297,3 +299,39 @@ int test_implicit_compare_with_functions() {
 
   return 1;
 }
+
+int strcmp_wrapper1(const char* a, const char* b) {
+  return strcmp(a, b);
+}
+
+int strcmp_wrapper2(const char* a, const char* b) {
+  return (a && b) ? strcmp(a, b) : 0;
+}
+
+#define macro_strncmp(s1, s2, n)                                              \
+  (__extension__ (__builtin_constant_p (n)                                    \
+                  && ((__builtin_constant_p (s1)                              \
+                       && strlen (s1) < ((size) (n)))                         \
+                      || (__builtin_constant_p (s2)                           \
+                          && strlen (s2) < ((size) (n))))                     \
+                  ? strcmp (s1, s2) : strncmp (s1, s2, n)))
+
+int strncmp_macro(const char* a, const char* b) {
+  if (macro_strncmp(a, b, 4))
+    return 0;
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: function 'strcmp' is called without explicitly comparing result
+
+  if (macro_strncmp(a, b, 4) == 2)
+    return 0;
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: function 'strcmp' is compared to a suspicious constant
+
+  if (macro_strncmp(a, b, 4) <= .0)
+    return 0;
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: function 'strcmp' has suspicious implicit cast
+
+  if (macro_strncmp(a, b, 4) + 0)
+    return 0;
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: results of function 'strcmp' used by operator '+'
+
+  return 1;
+}