Package org.spongepowered.asm.mixin.injection

Annotation Interface ModifyConstant

@Target(METHOD) @Retention(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.

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    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
    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.
    String[]
    method
    String representation of one or more target selectors which identify the target methods.
    int
    order
    By default almost all injectors for a target class apply their injections at the same time.
    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.
    Desc[]
    target
    Literal representation of one or more @Desc annotations which identify the target methods.

  • Element Details

    • method

      String[] method
      String representation of one or more target selectors which identify the target methods.
      Returns:
      target method(s) for this injector
      Default:
      {}

    • target

      Desc[] target
      Literal representation of one or more @Desc annotations which identify the target methods.
      Returns:
      target method(s) for this injector as descriptors
      Default:
      {}

    • slice

      Slice[] slice
      Array of Slice annotations which describe the method bisections used in locating target instructions for this modifier.
      Returns:
      slices
      Default:
      {}

    • constant

      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

      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

      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

      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

      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

      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:
      ""

    • order

      int order
      By default almost all injectors for a target class apply their injections at the same time. In other words, if multiple mixins target the same class then injectors are applied in priority order (since the mixins themselves are merged in priority order, and injectors run in the order they were merged). Redirect injectors apply in a later pass.

      The default order for redirect injectors is 10000, and all other injectors use 1000.

      Specifying a value for order alters this default behaviour and causes the injector to inject either earlier or later than it normally would. For example specifying 9900 will cause the injector to apply before others, while 11000 will apply later. Injectors with the same order will still apply in order of their mixin's priority.

      Returns:
      the application order for this injector, uses default REDIRECT order (10000) if not specified
      Default:
      10000