inject-locals.md

@Inject, locals

<- Return

Injects code into the target method, and allows capturing local variables. Needs @Inject(locals = ..) set to something other than NO_CAPTURE (default).

Parameters, in order:

• All target method parameters
• CallbackInfo (for void return type on target) or CallbackInfoReturnable<R>
• Local variables in scope up to the one needed.

Return type: see @Inject

Example mixin:

@Inject(method = "target()V", at = @At(value = "INVOKE", target = "Lnet/example/Dummy;dummy()V"), locals = LocalCapture.CAPTURE_FAILSOFT)
private void mixin(CallbackInfo ci, int i, int b) {
    if (i < b) {
        System.out.println(i + "<" + "b"));
    }
}

Method modification:

  public void target() {
  	  int i = 0;
      int b = 1;
      Dummy.getInstance().dummy();
+     {
+         if (i < b) {
+             System.out.println(i + "<" + "b"));
+         }
+     }
  }

locals must be one of the following values in order to capture locals:-

• LocalCapture.CAPTURE_FAILSOFT - Logs a warning and skips the injection if the calculated locals are different from the expected values.
• LocalCapture.CAPTURE_FAILHARD - Throws an error if the calculated locals are different from the expected values.
• LocalCapture.CAPTURE_FAILEXCEPTION - Throws an exception once the method is called if the calculated locals are different from the expected values

locals can also be LocalCapture.PRINT. Although this will not capture local variables, it prints expected method signature with local variables too. Example:-