Unreachable Code

ID

csharp.unreachable_code

Severity

low

Remediation Complexity

auto_fix

Remediation Risk

low

Remediation Effort

low

Resource

Dead Code

Language

CSharp

Tags

dead-code, reliability

Description

Reports a statement that can never execute because control flow always leaves the enclosing region before reaching it. The analysis walks the method’s control-flow graph: code becomes unreachable after an unconditional jump (return, throw, break, continue, goto), after a never-returning call (Environment.Exit(…​), Environment.FailFast(…​)), or inside an always-taken constant branch. Only the first statement of each dead region is flagged, and it is almost always a leftover from an earlier edit.

Rationale

C# itself produces a CS0162 warning for some of these cases, but only when the compiler can prove the preceding statement always exits. Structurally detecting "any statement after an unconditional exit in the same block" catches the broader category and surfaces the dead code as part of the regular quality pass instead of relying on warnings being turned on and not silenced.

public int Compute(int n)
{
    if (n < 0) throw new ArgumentException();
    return n * 2;
    int unused = 0;             // FLAW — statement after return
}

public void Loop()
{
    while (true)
    {
        break;
        DoWork();               // FLAW — statement after break
    }
}

public int Choose(bool flag)
{
    if (flag) return 1;         // OK — return is conditional, the rest still runs
    return 2;
}

Remediation

Delete the unreachable statements, or, if the control-flow exit was added by mistake, remove or guard the exit so the following statements run.

References