Update for clang-tidy 12 (#1644)

.clang-tidy

@@ -3,6 +3,7 @@ Checks: '
     bugprone-*,
     -bugprone-branch-clone,
     -bugprone-macro-parentheses,
+    -bugprone-narrowing-conversions,
     -bugprone-unhandled-self-assignment,
     google-*,
     -google-build-using-namespace,
@@ -24,10 +25,11 @@ Checks: '
     -modernize-use-trailing-return-type,
     -modernize-use-using,
     performance-*,
-    -performance-inefficient-string-concatenation,
+    -performance-no-int-to-ptr,
     portability-*,
     readability-*,
     -readability-else-after-return,
+    -readability-function-cognitive-complexity,
     -readability-function-size,
     -readability-implicit-bool-conversion,
     -readability-inconsistent-declaration-parameter-name,

src/curl_util.cpp

@@ -192,7 +192,9 @@ std::string get_canonical_headers(const struct curl_slist* list)
                 // skip empty-value headers (as they are discarded by libcurl)
                 continue;
             }
-            strhead       = strkey + ":" + strval;
+            strhead = strkey;
+            strhead += ":";
+            strhead += strval;
         }else{
             strhead = trim(lower(strhead));
         }
@@ -221,7 +223,9 @@ std::string get_canonical_headers(const struct curl_slist* list, bool only_amz)
                 // skip empty-value headers (as they are discarded by libcurl)
                 continue;
             }
-            strhead       = strkey + ":" + strval;
+            strhead = strkey;
+            strhead += ":";
+            strhead += strval;
         }else{
             strhead = trim(lower(strhead));
         }

src/s3fs.cpp

@@ -2699,7 +2699,7 @@ static int list_bucket(const char* path, S3ObjList& head, const char* delimiter,
 
     while(truncated){
         // append parameters to query in alphabetical order
-        std::string each_query = "";
+        std::string each_query;
         if(!next_continuation_token.empty()){
             each_query += "continuation-token=" + urlEncode(next_continuation_token) + "&";
             next_continuation_token = "";

src/string_util.cpp

@@ -471,7 +471,7 @@ unsigned char* s3fs_decode64(const char* input, size_t* plength)
 
 // Base location for transform.  The range 0xE000 - 0xF8ff
 // is a private range, se use the start of this range.
-static unsigned int escape_base = 0xe000;
+static const unsigned int escape_base = 0xe000;
 
 // encode bytes into wobbly utf8.  
 // 'result' can be null. returns true if transform was needed.