org.spongepowered.asm.mixin.injection

Annotation Type ModifyConstant

@Target(value=METHOD)
 @Retention(value=RUNTIME)
public @interface ModifyConstant

Specifies that this mixin method should inject a constant modifier callback to itself in the target method(s) identified by method() at the specified LDC (or specialised const opcode) instruction in order to adjust the constant value returned.

ModifyConstant callbacks should always take one argument of the appropriate constant type and return the same type. For example a ModifyConstant for a local of type String should have the signature:

private String methodName(String variable) { ...

The callback receives the original value of the constant, and should return the new value.

Like other Redirect injectors, the callback signature can optionally include the target method arguments by simply appending them to the handler method signature.

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
java.lang.String[]	method String representation of one or more MemberInfo which identify the target methods.

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
int	allow Injection points are in general expected to match every candidate instruction in the target method or slice, except in cases where options such as At.ordinal() are specified which naturally limit the number of results.
Constant[]	constant Discriminator for the constant(s) to match (injection points), if not specified then all constants matching the annotated handler's return type are matched
java.lang.String	constraints Returns constraints which must be validated for this injector to succeed.
int	expect Like require() but only enabled if the mixin.debug.countInjections option is set to true and defaults to 1.
boolean	remap By default, the annotation processor will attempt to locate an obfuscation mapping for all ModifyConstant methods since it is anticipated that in general the target of a ModifyConstant annotation will be an obfuscated method in the target class.
int	require In general, injectors are intended to "fail soft" in that a failure to locate the injection point in the target method is not considered an error condition.
Slice[]	slice Array of Slice annotations which describe the method bisections used in locating target instructions for this modifier.

Element Detail

method

public abstract java.lang.String[] method

String representation of one or more MemberInfo which identify the target methods.

Returns:

target method(s) for this injector

slice

public abstract Slice[] slice

Array of Slice annotations which describe the method bisections used in locating target instructions for this modifier.

Returns:

slices

Default:

{}

constant

public abstract Constant[] constant

Discriminator for the constant(s) to match (injection points), if not specified then all constants matching the annotated handler's return type are matched

Returns:

the constant discriminator

Default:

{}

remap

public abstract boolean remap

By default, the annotation processor will attempt to locate an obfuscation mapping for all ModifyConstant methods since it is anticipated that in general the target of a ModifyConstant annotation will be an obfuscated method in the target class. However since it is possible to also apply mixins to non-obfuscated targets (or non- obfuscated methods in obfuscated targets, such as methods added by Forge) it may be necessary to suppress the compiler error which would otherwise be generated. Setting this value to false will cause the annotation processor to skip this annotation when attempting to build the obfuscation table for the mixin.

Returns:

True to instruct the annotation processor to search for obfuscation mappings for this annotation

Default:

true

require

public abstract int require

In general, injectors are intended to "fail soft" in that a failure to locate the injection point in the target method is not considered an error condition. Another transformer may have changed the method structure or any number of reasons may cause an injection to fail. This also makes it possible to define several injections to achieve the same task given expected mutation of the target class and the injectors which fail are simply ignored.

However, this behaviour is not always desirable. For example, if your application depends on a particular injection succeeding you may wish to detect the injection failure as an error condition. This argument is thus provided to allow you to stipulate a minimum number of successful injections for this callback handler. If the number of injections specified is not achieved then an InjectionError is thrown at application time. Use this option with care.

Returns:

Minimum required number of injected callbacks, default specified by the containing config

Default:

-1

expect

public abstract int expect

Like require() but only enabled if the mixin.debug.countInjections option is set to true and defaults to 1. Use this option during debugging to perform simple checking of your injectors. Causes the injector to throw a InvalidInjectionException if the expected number of injections is not realised.

Returns:

Minimum number of expected callbacks, default 1

Default:

1

allow

public abstract int allow

Injection points are in general expected to match every candidate instruction in the target method or slice, except in cases where options such as At.ordinal() are specified which naturally limit the number of results.

This option allows for sanity-checking to be performed on the results of an injection point by specifying a maximum allowed number of matches, similar to that afforded by Group.max(). For example if your injection is expected to match 4 invocations of a target method, but instead matches 5, this can become a detectable tamper condition by setting this value to 4.

Setting any value 1 or greater is allowed. Values less than 1 or less than require() are ignored. require() supercedes this argument such that if allow is less than require the value of require is always used.

Note that this option is not a limit on the query behaviour of this injection point. It is only a sanity check used to ensure that the number of matches is not too high

Returns:

Maximum allowed number of injections for this

Default:

-1

constraints

public abstract java.lang.String constraints

Returns constraints which must be validated for this injector to succeed. See ConstraintParser.Constraint for details of constraint formats.

Returns:

Constraints for this annotation

Default:

""