Fix S4143: FP with List<T>.Add method calls

[cg110]

Description

Using the SonarAnalyzer.CSharp nuget, S4143 flags issues for List (and probably any lists)

Repro steps

Using the code:

List<string> S4143 = new List<string>();
S4143.Add("SomeText");
S4143.Add("\n");
S4143.Add("SomeText");
S4143.Add("\n");

The last 2 Adds are showing with warnings for S4143, as they are Adds they're extending the list rather than overwriting any existing entries.

Expected behavior

The above code shouldn't generate a warning.

Actual behavior

S4143 generates warnings.

Known workarounds

Set the warning to info or suppress.

Related information

• SonarC# Version: 7.16.0.8981
• Visual Studio Version: 2017, 15.9.16
• If running through the Scanner for MSBuild, its version

[Corniel]

I think it is okay that this warning is shown. You could argue that this behaviour should not be applied on a List<string>, but I think that adding string literals to a list this way is a bad practice.

You could argue that the message should than be different, but it tells you (indirectly) why this is a bad practice: a list is intended for keeping track of multiple elements of T (string in this case), not for building dynamic text. (Then you should use StringBuilder.)

[cg110]

I'd argue that a list is allowed to have duplicate entries in it, if I wanted unique then I'd be using a dictionary or hashset.

[christophe-zurn-sonarsource]

Hello @cg110 , thanks for reporting this.
Considering the rule, it is indeed a false positive, as the elements added later are not overriding the previous ones.