From 90c7db15a018cbefcf8c733cee5aec6a9b32414e Mon Sep 17 00:00:00 2001
From: Richard Quirk <richard.quirk@gmail.com>
Date: Fri, 28 Oct 2011 22:05:11 +0200
Subject: [PATCH] Add check for comparison of identical string variables

---
 lib/checkother.cpp | 19 +++++++++++++++++++
 lib/checkother.h   |  2 ++
 test/testother.cpp | 10 ++++++++++
 3 files changed, 31 insertions(+)

diff --git a/lib/checkother.cpp b/lib/checkother.cpp
index 764a2ccaf..a5ebea7ee 100644
--- a/lib/checkother.cpp
+++ b/lib/checkother.cpp
@@ -2257,6 +2257,7 @@ void CheckOther::checkAlwaysTrueOrFalseStringCompare()
 
     const char pattern1[] = "strncmp|strcmp|stricmp|strcmpi|strcasecmp|wcscmp ( %str% , %str% ";
     const char pattern2[] = "QString :: compare ( %str% , %str% )";
+    const char pattern3[] = "strncmp|strcmp|stricmp|strcmpi|strcasecmp|wcscmp ( %var% , %var% ";
 
     const Token *tok = _tokenizer->tokens();
     while (tok && (tok = Token::findmatch(tok, pattern1)) != NULL) {
@@ -2269,6 +2270,14 @@ void CheckOther::checkAlwaysTrueOrFalseStringCompare()
         alwaysTrueFalseStringCompareError(tok, tok->strAt(4), tok->strAt(6));
         tok = tok->tokAt(7);
     }
+
+    tok = _tokenizer->tokens();
+    while (tok && (tok = Token::findmatch(tok, pattern3)) != NULL) {
+        const Token *var1 = tok->tokAt(2);
+        const Token *var2 = tok->tokAt(4);
+        alwaysTrueStringVariableCompareError(tok, var1->str(), var2->str());
+        tok = tok->tokAt(5);
+    }
 }
 
 void CheckOther::alwaysTrueFalseStringCompareError(const Token *tok, const std::string& str1, const std::string& str2)
@@ -2291,6 +2300,16 @@ void CheckOther::alwaysTrueFalseStringCompareError(const Token *tok, const std::
     }
 }
 
+void CheckOther::alwaysTrueStringVariableCompareError(const Token *tok, const std::string& str1, const std::string& str2)
+{
+    if (str1 == str2) {
+        reportError(tok, Severity::warning, "stringCompare",
+                    "Comparison of identical string variables.\n"
+                    "The compared strings, '" + str1 + "' and '" + str2 + "', are identical. "
+                    "This could be a logic bug.");
+    }
+}
+
 //-----------------------------------------------------------------------------
 //-----------------------------------------------------------------------------
 void CheckOther::sizeofsizeof()
diff --git a/lib/checkother.h b/lib/checkother.h
index 8dcd03133..60ec133e3 100644
--- a/lib/checkother.h
+++ b/lib/checkother.h
@@ -273,6 +273,7 @@ public:
     void duplicateBranchError(const Token *tok1, const Token *tok2);
     void duplicateExpressionError(const Token *tok1, const Token *tok2, const std::string &op);
     void alwaysTrueFalseStringCompareError(const Token *tok, const std::string& str1, const std::string& str2);
+    void alwaysTrueStringVariableCompareError(const Token *tok, const std::string& str1, const std::string& str2);
     void duplicateBreakError(const Token *tok);
     void assignBoolToPointerError(const Token *tok);
     void unsignedLessThanZeroError(const Token *tok, const std::string &varname);
@@ -326,6 +327,7 @@ public:
         c.duplicateBranchError(0, 0);
         c.duplicateExpressionError(0, 0, "&&");
         c.alwaysTrueFalseStringCompareError(0, "str1", "str2");
+        c.alwaysTrueStringVariableCompareError(0, "varname1", "varname2");
         c.duplicateBreakError(0);
         c.unsignedLessThanZeroError(0, "varname");
         c.unsignedPositiveError(0, "varname");
diff --git a/test/testother.cpp b/test/testother.cpp
index 5b18f3470..c27c2f003 100644
--- a/test/testother.cpp
+++ b/test/testother.cpp
@@ -3428,6 +3428,16 @@ private:
             "  }"
             "}");
         ASSERT_EQUALS("[test.cpp:3]: (warning) Comparison of always identical static strings.\n", errout.str());
+
+        check_preprocess_suppress(
+            "int foo(const char *buf)\n"
+            "{\n"
+            "  if (strcmp(buf, buf) == 0)"
+            "  {"
+            "    std::cout << \"Equal\n\""
+            "  }"
+            "}");
+        ASSERT_EQUALS("[test.cpp:3]: (warning) Comparison of identical string variables.\n", errout.str());
     }
 
     void check_signOfUnsignedVariable(const char code[]) {