Mark export/unexport as deprecated

Make it so that `export`/`unexport` are deprecated during product
configuration, but obsolete during Android.mk parsing (and later in the
build, since we can't un-obsolete it).

Remove some ccache / goma exports, those don't need to be exports, since
soong_ui asks about them explicitly. They also only run doing the
initial project configuration, so we don't run anything with that
environment.

Bug: 73959648
Test: m nothing
Test: build_test on all downstream branches
Change-Id: I55a749f46775660439ae57e881a02c914e83de16

Changes.md

@@ -1,5 +1,55 @@
 # Build System Changes for Android.mk Writers
 
+### `export` and `unexport` deprecation  {#export_keyword}
+
+The `export` and `unexport` keywords have been deprecated, and will throw
+warnings or errors depending on where they are used.
+
+Early in the make system, during product configuration and BoardConfig.mk
+reading: these will throw a warnings, and will be an error in the future.
+Device specific configuration should not be able to affect common core build
+steps -- we're looking at triggering build steps to be invalidated if the set
+of environment variables they can access changes. If device specific
+configuration is allowed to change those, switching devices with the same
+output directory could become significantly more expensive than it already can
+be.
+
+Later, during Android.mk files, and later tasks: these will throw errors, since
+it is increasingly likely that they are being used incorrectly, attempting to
+change the environment for a single build step, and instead setting it for
+hundreds of thousands.
+
+It is not recommended to just move the environment variable setting outside of
+the build (in vendorsetup.sh, or some other configuration script or wrapper).
+We expect to limit the environment variables that the build respects in the
+future, others will be cleared. (There will be methods to get custom variables
+into the build, just not to every build step)
+
+Instead, write the export commands into the rule command lines themselves:
+
+``` make
+$(intermediates)/generated_output.img:
+	rm -rf $@
+	export MY_ENV_A="$(MY_A)"; make ...
+```
+
+If you want to set many environment variables, and/or use them many times,
+write them out to a script and source the script:
+
+``` make
+envsh := $(intermediates)/env.sh
+$(envsh):
+	rm -rf $@
+	echo 'export MY_ENV_A="$(MY_A)"' >$@
+	echo 'export MY_ENV_B="$(MY_B)"' >>$@
+
+$(intermediates)/generated_output.img: PRIVATE_ENV := $(envsh)
+$(intermediates)/generated_output.img: $(envsh) a/b/c/package.sh
+	rm -rf $@
+	source $(PRIVATE_ENV); make ...
+	source $(PRIVATE_ENV); a/b/c/package.sh ...
+```
+
 ## Implicit make rules are deprecated {#implicit_rules}
 
 Implicit rules look something like the following:

core/ccache.mk

@@ -32,24 +32,24 @@ ifneq ($(CCACHE_EXEC),)
 ifneq ($(filter-out false,$(USE_CCACHE)),)
   # The default check uses size and modification time, causing false misses
   # since the mtime depends when the repo was checked out
-  export CCACHE_COMPILERCHECK ?= content
+  CCACHE_COMPILERCHECK ?= content
 
   # See man page, optimizations to get more cache hits
   # implies that __DATE__ and __TIME__ are not critical for functionality.
   # Ignore include file modification time since it will depend on when
   # the repo was checked out
-  export CCACHE_SLOPPINESS := time_macros,include_file_mtime,file_macro
+  CCACHE_SLOPPINESS := time_macros,include_file_mtime,file_macro
 
   # Turn all preprocessor absolute paths into relative paths.
   # Fixes absolute paths in preprocessed source due to use of -g.
   # We don't really use system headers much so the rootdir is
   # fine; ensures these paths are relative for all Android trees
   # on a workstation.
-  export CCACHE_BASEDIR := /
+  CCACHE_BASEDIR := /
 
   # Workaround for ccache with clang.
   # See http://petereisentraut.blogspot.com/2011/09/ccache-and-clang-part-2.html
-  export CCACHE_CPP2 := true
+  CCACHE_CPP2 := true
 
   ifndef CC_WRAPPER
     CC_WRAPPER := $(CCACHE_EXEC)

core/config.mk

@@ -85,6 +85,9 @@ $(KATI_obsolete_var \
 $(KATI_obsolete_var PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE,Set FCM Version in device manifest instead. See $(CHANGES_URL)#PRODUCT_COMPATIBILITY_MATRIX_LEVEL_OVERRIDE)
 $(KATI_obsolete_var USE_CLANG_PLATFORM_BUILD,Clang is the only supported Android compiler. See $(CHANGES_URL)#USE_CLANG_PLATFORM_BUILD)
 
+# This is marked as obsolete in envsetup.mk after reading the BoardConfig.mk
+$(KATI_deprecate_export It is a global setting. See $(CHANGES_URL)#export_keyword)
+
 CHANGES_URL :=
 
 # Used to force goals to build.  Only use for conditionally defined goals.
@@ -358,10 +361,6 @@ endif
 ifeq ($(CALLED_FROM_SETUP),true)
 include $(BUILD_SYSTEM)/ccache.mk
 include $(BUILD_SYSTEM)/goma.mk
-
-export CC_WRAPPER
-export CXX_WRAPPER
-export JAVAC_WRAPPER
 endif
 
 ifdef TARGET_PREFER_32_BIT

core/envsetup.mk

@@ -288,6 +288,14 @@ $(foreach var,$(vars), \
 
 .KATI_READONLY := $(vars)
 
+CHANGES_URL := https://android.googlesource.com/platform/build/+/master/Changes.md
+
+# "" is equivalent to true currently.
+ifeq ($(BUILD_BROKEN_ANDROIDMK_EXPORTS),false)
+$(KATI_obsolete_export It is a global setting. See $(CHANGES_URL)#export_keyword)
+endif
+
+CHANGES_URL :=
 
 ###########################################
 # Now we can substitute with the real value of TARGET_COPY_OUT_VENDOR

core/goma.mk

@@ -14,9 +14,6 @@
 # limitations under the License.
 #
 
-# Used by the compiler wrapper, but should only be set by gomacc
-unexport GOMACC_PATH
-
 # Notice: this works only with Google's Goma build infrastructure.
 ifneq ($(filter-out false,$(USE_GOMA)),)
   # Goma requires a lot of processes and file descriptors.