Warnversion Warning Waves.md

/warn warning "waves"

The C# compiler flag /warn controls optional warnings. When we introduce new warnings that can be reported on existing code, we do so under an opt-in system so that programmers do not see new warnings without taking action to enable them. For that purpose, we have the compiler flag "/warn:n" where n is a whole number.

The compiler shipped with dotnet 5 (the C# 9 compiler) contains some warnings, documented below, that are reported only under /warn:5 or higher.

The default warning level when the command-line compiler is used is 4.

If you want the compiler to produce all applicable warnings, you can specify /warn:9999.

The table below describes all of the warnings controlled by warning levels 5 or greater.

Warning ID	warning level	Description
CS7023	5	A static type is used in an 'is' or 'as' expression
CS8073	5	Expression always true (or false) when comparing a struct to null
CS8848	5	Diagnose precedence error with query expression
CS8880	5	Struct constructor does not assign auto property (imported struct type with private fields)
CS8881	5	Struct constructor does not assign field (imported struct type with private fields)
CS8882	5	Out parameter not assigned (imported struct type with private fields)
CS8883	5	Auto-property used before assigned in struct constructor (imported struct type with private fields)
CS8884	5	Field used before assigned in struct constructor (imported struct type with private fields)
CS8885	5	Struct constructor reads 'this' before assigning all fields (imported struct type with private fields)
CS8886	5	Out parameter used before being assigned (imported struct type with private fields)
CS8887	5	Local variable used before being assigned (imported struct type with private fields)