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Commit 08a76dd7 authored by Automerger Merge Worker's avatar Automerger Merge Worker
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Merge "Document the m4 prebuilts" am: 474de20a am: 3abf2ee0

Change-Id: I6982af43553d159a164b4bf985feb19db022fed2
parents cb807e94 3abf2ee0
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# Build System Changes for Android.mk Writers

## `m4` is not available on `$PATH`

There is a prebuilt of it available in prebuilts/build-tools, and a make
variable `M4` that contains the path.

Beyond the direct usage, whenever you use bison or flex directly, they call m4
behind the scene, so you must set the M4 environment variable (and depend upon
it for incremental build correctness):

```
$(intermediates)/foo.c: .KATI_IMPLICIT_OUTPUTS := $(intermediates)/foo.h
$(intermediates)/foo.c: $(LOCAL_PATH)/foo.y $(M4) $(BISON) $(BISON_DATA)
	M4=$(M4) $(BISON) ...
```

## Rules executed within limited environment

With `ALLOW_NINJA_ENV=false` (soon to be the default), ninja, and all the