Show struct member in unsignedLessThanZeroError warning

Before:
    [/tmp/test.c:8]: (style) Checking if unsigned variable '.' is less than zero.
    [/tmp/test.c:12]: (style) Checking if unsigned variable '.' is less than zero.

After:
    [/tmp/test.c:8]: (style) Checking if unsigned variable 'd.n' is less than zero.
    [/tmp/test.c:12]: (style) Checking if unsigned variable 'd.n' is less than zero.

lib/checkother.cpp

@@ -2157,13 +2157,13 @@ void CheckOther::checkSignOfUnsignedVariable()
                 if (vt && vt->pointer)
                     pointerLessThanZeroError(tok, inconclusive);
                 if (vt && vt->sign == ValueType::UNSIGNED)
-                    unsignedLessThanZeroError(tok, tok->astOperand1()->str(), inconclusive);
+                    unsignedLessThanZeroError(tok, tok->astOperand1()->expressionString(), inconclusive);
             } else if (Token::Match(tok->previous(), "0 >|>=") && tok->previous() == tok->astOperand1()) {
                 const ValueType* vt = tok->astOperand2()->valueType();
                 if (vt && vt->pointer)
                     pointerLessThanZeroError(tok, inconclusive);
                 if (vt && vt->sign == ValueType::UNSIGNED)
-                    unsignedLessThanZeroError(tok, tok->astOperand2()->str(), inconclusive);
+                    unsignedLessThanZeroError(tok, tok->astOperand2()->expressionString(), inconclusive);
             } else if (Token::simpleMatch(tok, ">= 0") && tok->next() == tok->astOperand2()) {
                 const ValueType* vt = tok->astOperand1()->valueType();
                 if (vt && vt->pointer)

lib/token.cpp

@@ -1146,6 +1146,51 @@ bool Token::isUnaryPreOp() const
     return false; // <- guess
 }
 
+static const Token* goToLeftParenthesis(const Token* start, const Token* end)
+{
+    // move start to lpar in such expression: '(*it).x'
+    int par = 0;
+    for (const Token *tok = start; tok && tok != end; tok = tok->next()) {
+        if (tok->str() == "(")
+            ++par;
+        else if (tok->str() == ")") {
+            if (par == 0)
+                start = tok->link();
+            else
+                --par;
+        }
+    }
+    return start;
+}
+
+static const Token* goToRightParenthesis(const Token* start, const Token* end)
+{
+    // move end to rpar in such expression: '2>(x+1)'
+    int par = 0;
+    for (const Token *tok = end; tok && tok != start; tok = tok->previous()) {
+        if (tok->str() == ")")
+            ++par;
+        else if (tok->str() == "(") {
+            if (par == 0)
+                end = tok->link();
+            else
+                --par;
+        }
+    }
+    return end;
+}
+
+static std::string stringFromTokenRange(const Token* start, const Token* end)
+{
+    std::string ret;
+    for (const Token *tok = start; tok && tok != end; tok = tok->next()) {
+        ret += tok->str();
+        if (Token::Match(tok, "%name%|%num% %name%|%num%"))
+            ret += " ";
+    }
+    return ret + end->str();
+}
+
 std::string Token::expressionString() const
 {
     const Token * const top = this;
@@ -1163,39 +1208,10 @@ std::string Token::expressionString() const
         end = end->astOperand2() ? end->astOperand2() : end->astOperand1();
     }
 
-    // move start to lpar in such expression: '(*it).x'
-    int par = 0;
-    for (const Token *tok = start; tok && tok != end; tok = tok->next()) {
-        if (tok->str() == "(")
-            ++par;
-        else if (tok->str() == ")") {
-            if (par == 0)
-                start = tok->link();
-            else
-                --par;
-        }
-    }
+    start = goToLeftParenthesis(start, end);
+    end = goToRightParenthesis(start, end);
 
-    // move end to rpar in such expression: '2>(x+1)'
-    par = 0;
-    for (const Token *tok = end; tok && tok != start; tok = tok->previous()) {
-        if (tok->str() == ")")
-            ++par;
-        else if (tok->str() == "(") {
-            if (par == 0)
-                end = tok->link();
-            else
-                --par;
-        }
-    }
-
-    std::string ret;
-    for (const Token *tok = start; tok && tok != end; tok = tok->next()) {
-        ret += tok->str();
-        if (Token::Match(tok, "%name%|%num% %name%|%num%"))
-            ret += " ";
-    }
-    return ret + end->str();
+    return stringFromTokenRange(start, end);
 }
 
 static void astStringXml(const Token *tok, std::size_t indent, std::ostream &out)

test/testother.cpp

@@ -170,6 +170,8 @@ private:
         TEST_CASE(testEvaluationOrderSequencePointsFunctionCall);
         TEST_CASE(testEvaluationOrderSequencePointsComma);
         TEST_CASE(testEvaluationOrderSizeof);
+
+        TEST_CASE(testUnsignedLessThanZero);
     }
 
     void check(const char code[], const char *filename = nullptr, bool experimental = false, bool inconclusive = true, bool runSimpleChecks=true, Settings* settings = 0) {
@@ -6053,6 +6055,27 @@ private:
               "}", "test.c");
         ASSERT_EQUALS("", errout.str());
     }
+
+    void testUnsignedLessThanZero() {
+        check("struct d {\n"
+              "  unsigned n;\n"
+              "};\n"
+              "void f(void) {\n"
+              "  struct d d;\n"
+              "  d.n = 3;\n"
+              "\n"
+              "  if (d.n < 0) {\n"
+              "    return;\n"
+              "  }\n"
+              "\n"
+              "  if (0 > d.n) {\n"
+              "    return;\n"
+              "  }\n"
+              "}", "test.c");
+        ASSERT_EQUALS("[test.c:8]: (style) Checking if unsigned variable 'd.n' is less than zero.\n"
+                      "[test.c:12]: (style) Checking if unsigned variable 'd.n' is less than zero.\n",
+                      errout.str());
+    }
 };
 
 REGISTER_TEST(TestOther)