CA1508: Avoid dead conditional code

บทความ
04/22/2023

Property	Value
Rule ID	CA1508
Title	Avoid dead conditional code
Category	Maintainability
Fix is breaking or non-breaking	Non-Breaking
Enabled by default in .NET 9	No

Cause

A method has conditional code that always evaluates to true or false at run time. This leads to dead code in the false branch of the condition.

By default, this rule analyzes the entire codebase, but this is configurable.

Rule description

Methods can have conditional code, such as if statements, binary expressions (==, !=, <, >), null checks, etc. For example, consider the following code:

public void M(int i, int j)
{
    if (i != 0)
    {
        return;
    }

    if (j != 0)
    {
        return;
    }

    // Below condition will always evaluate to 'false' as 'i' and 'j' are both '0' here.
    if (i != j)
    {
        // Code in this 'if' branch is dead code.
        // It can either be removed or refactored.
        ...
    }
}

C# and VB compilers perform analysis of conditional checks involving compile-time constant values that always evaluate to true or false. This analyzer performs data flow analysis of non-constant variables to determine redundant conditional checks involving non-constant values. In the preceding code, the analyzer determines that i and j are both 0 for all code paths that reach i != j check. Hence, this check will always evaluate to false at run time. The code inside the if statement is dead code and can be removed or refactored. Similarly, the analyzer tracks nullness of variables and reports redundant null checks.

Note

This analyzer performs an expensive dataflow analysis of non-constant values. This can increase the overall compile time on certain code bases.

When to suppress warnings

It's safe to suppress a violation of this rule if you're not concerned about the maintainability of your code. It is also fine to suppress violations that are identified to be false positives. These are possible in the presence of concurrent code that can execute from multiple threads.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1508
// The code that's violating the rule is on this line.
#pragma warning restore CA1508

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1508.severity = none

For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following options to configure which parts of your codebase to run this rule on.

Exclude specific symbols
Exclude specific types and their derived types

You can configure these options for just this rule, for all rules it applies to, or for all rules in this category (Maintainability) that it applies to. For more information, see Code quality rule configuration options.

Exclude specific symbols

You can exclude specific symbols, such as types and methods, from analysis. For example, to specify that the rule should not run on any code within types named MyType, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType

Allowed symbol name formats in the option value (separated by |):

Symbol name only (includes all symbols with the name, regardless of the containing type or namespace).
Fully qualified names in the symbol's documentation ID format. Each symbol name requires a symbol-kind prefix, such as M: for methods, T: for types, and N: for namespaces.
.ctor for constructors and .cctor for static constructors.

Examples:

Option Value	Summary
`dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType`	Matches all symbols named `MyType`.
`dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType1\|MyType2`	Matches all symbols named either `MyType1` or `MyType2`.
`dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS.MyType.MyMethod(ParamType)`	Matches specific method `MyMethod` with the specified fully qualified signature.
`dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS1.MyType1.MyMethod1(ParamType)\|M:NS2.MyType2.MyMethod2(ParamType)`	Matches specific methods `MyMethod1` and `MyMethod2` with the respective fully qualified signatures.

Exclude specific types and their derived types

You can exclude specific types and their derived types from analysis. For example, to specify that the rule should not run on any methods within types named MyType and their derived types, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType