From 381c38b2f5c8476f6a10d87130fcea5d85839cf8 Mon Sep 17 00:00:00 2001
From: chrchr-github <78114321+chrchr-github@users.noreply.github.com>
Date: Tue, 12 Jul 2022 17:40:14 +0200
Subject: [PATCH] Improve check: uselessCallsConstructor (#4270)

---
 lib/checkstl.cpp | 10 ++++++++++
 lib/checkstl.h   |  1 +
 test/teststl.cpp | 30 ++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/lib/checkstl.cpp b/lib/checkstl.cpp
index a7ed835c0..793523c24 100644
--- a/lib/checkstl.cpp
+++ b/lib/checkstl.cpp
@@ -2175,6 +2175,10 @@ void CheckStl::uselessCalls()
                 uselessCallsEmptyError(tok->next());
             else if (Token::Match(tok, "[{};] std :: remove|remove_if|unique (") && tok->tokAt(5)->nextArgument())
                 uselessCallsRemoveError(tok->next(), tok->strAt(3));
+            else if (printPerformance && Token::Match(tok, "%var% = { %var% . begin ( ) ,") &&
+                     tok->valueType() && tok->valueType()->type == ValueType::CONTAINER && tok->varId() == tok->tokAt(3)->varId()) {
+                uselessCallsConstructorError(tok);
+            }
         }
     }
 }
@@ -2223,6 +2227,12 @@ void CheckStl::uselessCallsSubstrError(const Token *tok, SubstrErrorType type)
     reportError(tok, Severity::performance, "uselessCallsSubstr", msg, CWE398, Certainty::normal);
 }
 
+void CheckStl::uselessCallsConstructorError(const Token *tok)
+{
+    const std::string msg = "Inefficient constructor call: container '" + tok->str() + "' is assigned a partial copy of itself. Use erase() or resize() instead.";
+    reportError(tok, Severity::performance, "uselessCallsConstructor", msg, CWE398, Certainty::normal);
+}
+
 void CheckStl::uselessCallsEmptyError(const Token *tok)
 {
     reportError(tok, Severity::warning, "uselessCallsEmpty", "Ineffective call of function 'empty()'. Did you intend to call 'clear()' instead?", CWE398, Certainty::normal);
diff --git a/lib/checkstl.h b/lib/checkstl.h
index dd450fb2e..11e38e649 100644
--- a/lib/checkstl.h
+++ b/lib/checkstl.h
@@ -224,6 +224,7 @@ private:
     void uselessCallsSubstrError(const Token* tok, SubstrErrorType type);
     void uselessCallsEmptyError(const Token* tok);
     void uselessCallsRemoveError(const Token* tok, const std::string& function);
+    void uselessCallsConstructorError(const Token* tok);
 
     void dereferenceInvalidIteratorError(const Token* deref, const std::string& iterName);
     void dereferenceInvalidIteratorError(const Token* tok, const ValueFlow::Value *value, bool inconclusive);
diff --git a/test/teststl.cpp b/test/teststl.cpp
index 8656824ba..2ac0aa57e 100644
--- a/test/teststl.cpp
+++ b/test/teststl.cpp
@@ -4183,6 +4183,36 @@ private:
               "}\n");
         ASSERT_EQUALS("[test.cpp:2]: (performance) Ineffective call of function 'substr' because a prefix of the string is assigned to itself. Use replace() instead.\n",
                       errout.str());
+
+        check("std::string f(std::string s, std::size_t end) {\n"
+              "    s = { s.begin(), s.begin() + end };\n"
+              "    return s;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2]: (performance) Inefficient constructor call: container 's' is assigned a partial copy of itself. Use erase() or resize() instead.\n",
+                      errout.str());
+
+        check("std::list<int> f(std::list<int> l, std::size_t end) {\n"
+              "    l = { l.begin(), l.begin() + end };\n"
+              "    return l;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2]: (performance) Inefficient constructor call: container 'l' is assigned a partial copy of itself. Use erase() or resize() instead.\n",
+                      errout.str());
+
+        check("std::string f(std::string s, std::size_t end) {\n"
+              "    s = std::string{ s.begin(), s.begin() + end };\n"
+              "    return s;\n"
+              "}\n");
+        TODO_ASSERT_EQUALS("[test.cpp:2]: (performance) Inefficient constructor call: container 's' is assigned a partial copy of itself. Use erase() or resize() instead.\n",
+                           "",
+                           errout.str());
+
+        check("std::string f(std::string s, std::size_t end) {\n"
+              "    s = std::string(s.begin(), s.begin() + end);\n"
+              "    return s;\n"
+              "}\n");
+        TODO_ASSERT_EQUALS("[test.cpp:2]: (performance) Inefficient constructor call: container 's' is assigned a partial copy of itself. Use erase() or resize() instead.\n",
+                           "",
+                           errout.str());
     }
 
     void stabilityOfChecks() {