Create rule S7121 Calls to c_str() should not implicitly recreate strings or string_views CPP-3435

rules/S7121/cfamily/metadata.json

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+{
+  "title": "Calls to c_str() should not implicitly recreate strings or string_views",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [
+  ],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-7121",
+  "sqKey": "S7121",
+  "scope": "All",
+  "defaultQualityProfiles": ["Sonar way"],
+  "quickfix": "targeted",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "MEDIUM"
+    },
+    "attribute": "EFFICIENT"
+  }
+}

rules/S7121/cfamily/rule.adoc

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+Unnecessary calls to `c_str()` or `data()` reduce readability and performance.
+
+== Why is this an issue?
+
+In the process of refactoring code from C to C++, it can easily happen that redundant calls to `c_str()`
+or `data()` on standard strings or string_views get introduced when the original string could be used directly.
+
+[source,cpp,diff-id=1,diff-type=noncompliant]
+----
+void takeString(std::string const& dest);
+
+void takeStringView(std::string_view dest);
+
+void func(std::string const& src, std::string_view srcView) {
+  takeString(src.c_str()); // Noncompliant: redundant copy
+  takeStringView(src.c_str()); // Noncompliant: redundant copy
+  takeStringView(srcView.data()); // Noncompliant: redundant crossing of the content
+}
+----
+
+Not only is this unnecessary step a readability issue, but it will force the creation of useless intermediary strings,
+or force to cross the content of a string_view to search for the null-terminator, reducing the performance.
+The call to `c_str()` or `data()` should be removed.
+
+[source,cpp,diff-id=1,diff-type=compliant]
+----
+void takeString(std::string const& dest);
+
+void takeStringView(std::string_view dest);
+
+void func(std::string const& src, std::string_view srcView) {
+  takeString(src); // Compliant
+  takeStringView(src); // Compliant
+  takeStringView(srcView); // Compliant
+}
+----
+
+=== Exception
+
+This rule does not raise when explicitly creating a string or a string_view from `c_str()`.
+
+[source,cpp]
+----
+void takeString(std::string const& dest);
+
+void func(std::string const& src) {
+  takeString(std::string(src.c_str())); // Compliant by exception
+}
+----
+
+This operation could be done on purpose in the rare case where `src` is a string containing embedded null-terminators, in order to only keep the content up to the first null-terminator in `dest`.
+
+== Resources
+
+=== Related rules
+
+* S6231 - "std::string_view" and "std::span" parameters should be directly constructed from sequences

rules/S7121/metadata.json

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+{
+}