misra.py: Fix R21.1 FalsePositive on standard functions and errno (#2339)

Rule 21.1 now doesn't report errors on usage of library functions
started from underscore (e.g. `_exit') and valid errno assignment.

See added tests for examples.

addons/misra.py

@@ -16,6 +16,7 @@
 from __future__ import print_function
 
 import cppcheckdata
+import itertools
 import sys
 import re
 import os
@@ -1964,10 +1965,16 @@ class MisraChecker:
             if res:
                 self.reportError(directive, 21, 1)
 
+        type_name_tokens = (t for t in data.tokenlist if t.typeScopeId)
+        type_fields_tokens = (t for t in data.tokenlist if t.valueType and t.valueType.typeScopeId)
+
         # Search for forbidden identifiers
-        for token in data.tokenlist:
-            if not token.isName:
-                continue
+        for i in itertools.chain(data.variables, data.functions, type_name_tokens, type_fields_tokens):
+            token = i
+            if isinstance(i, cppcheckdata.Variable):
+                token = i.nameToken
+            elif isinstance(i, cppcheckdata.Function):
+                token = i.tokenDef
             if len(token.str) < 2:
                 continue
             if token.str == 'errno':

addons/test/misra/misra-test.c

@@ -733,7 +733,7 @@ union misra_19_2 { }; // 19.2
 #define __Incompatible 0xdeadbeef // 21.1
 #define __starts_with_lower 0xdeadbeef // 21.1
 #define __MY_HEADER_ // 21.1
-#define _starts_with_lower 1 // no warning
+#define _macro_starts_with_lower 1 // no warning
 static int _file_scope_id_21_1 = 42; // no warning
 static int _file_scope_id_21_1_fn() { return 42; } // no warning
 static int __file_scope_id_21_1 = 42; // 21.1
@@ -746,19 +746,23 @@ int __external_scope_id_21_1 = 42; // 21.1
 int __external_scope_id_21_1_fn() { return 42; } // 21.1
 int _External_scope_id_21_1 = 42; // 21.1
 int _External_scope_id_21_1_fn() { return 42; } // 21.1
-int errno = 42; // 21.1
-int errno() { // 21.1
-    // TODO: 15.5 false positive
-    return 42; // 15.5
+int errno = 42; // 21.1 5.5
+int misra_21_1() {
+    int _a = 42; // 21.1
+    errno = EINVAL; // no warning
+    _a ++; // no warning
+    _exit(1); // no warning
+    return _a; // no warning
 }
-
+int _misra_21_1_1(); // 21.1
+static int _misra_21_1_2(); // no warning
+#define errno 11 // 21.1
 struct _struct_21_1 { int a; }; // 21.1
 struct _Struct_21_1 { int a; }; // 21.1
 struct __struct_21_1 { int a; }; // 21.1
 typedef struct { int a; } _struct_21_1_t; // 21.1
 typedef struct { int a; } _Struct_21_1_t; // 21.1
 typedef struct { int a; } __struct_21_1_t; // 21.1
-
 enum _enum_21_1 { ENUM211_1 }; // 21.1
 enum _Enum_21_1 { ENUM211_2 }; // 21.1
 enum __enum_21_1 { ENUM211_3 }; // 21.1
@@ -773,7 +777,6 @@ enum enum_21_1_valid_id {
     _eNUM211_10, // 21.1
     enum211_11
 };
-
 union _union_21_1 { int a; }; // 21.1 19.2
 union _Union_21_1 { int a; }; // 21.1 19.2
 union __union_21_1 { int a; }; // 21.1 19.2