Fix S1172 FP: case when where the pattern is a constant

[tsleegers]

Description

When a function parameter only is used in het when clause of pattern matching in a switch statement it incorrecty marks that parameter as unused (S1172)

Repro steps

Please provide the steps required to reproduce the problem

Example code:

static int PatternMatch(StringSplitOptions splitOptions, int i)
{
    switch (splitOptions)
    {
        case StringSplitOptions.None
            when i > 0:
            return 1;
        default:
            return 0;
    }
}

Parameter i is marked unused.

Expected behavior

No warning from sonar analyzers.

Actual behavior

S1172 warning generated:
Warning S1172 Remove this parameter 'i', whose value is ignored in the method.

Known workarounds

Suppress warning.

Related information

• SonarC# Version: 7.7.0.7192
• Visual Studio Version: Visual Studio Professional 2017 (15.8.7 and 15.9.0 Preview 3)

[valhristov]

Thanks for reporting this problem @tsleegers, I managed to reproduce it, we will fix it in a future release.

Note to implementers: for this to be fixed the Live Variable Analysis needs to start analysing patterns.

[Herdo]

@valhristov Is there any progress on this issue?

[Herdo]

Or @andrei-epure-sonarsource ?

[andrei-epure-sonarsource]

@Herdo no progress yet. We plan to invest some effort this year to improve our Control Flow Graph.