ccache.bbclass: Refactor it to make it more reliable

The previous ccache.bbclass has the following problems:
- It uses host's ccache for native recipes, but this may not work on some
  hosts, for example, it nerver works on my Ubuntu 14.04.4, there are always
  build failures (m4-native failed at do_configure, and others will also be
  failed if I disable CCACHE for m4-native)

- native/nativesdk/cross/crosssdk recipes use host's ccache, but target uses
  ccache-native, this may confuse user.

- The target recipes may use both host's ccache and ccache-native, this may
  cause unexpected problems and be hard to debug. This is because ccache-native is
  in SIGGEN_EXCLUDE_SAFE_RECIPE_DEPS, so ccache-native may not be present when
  rebuild target recipes, and then it would use hosttools/ccache, but the
  previous ccache files were generated by ccache-native.

- Target recipes can't use ccache when no ccache is installed on the host:
  CCACHE = "${@bb.utils.which(d.getVar('PATH'), 'ccache') and 'ccache '}"

After refactored:
All types recipes (native, target and others) will use ccache-native except
ccache-native itself, host's cache won't be used any more. It is more
reliable now, which will work everywhere when ccache-native can be built.

And now we need use "CCACHE_DISABLE = '1'" to disable ccache for the recipe
rather than "CCACHE = ''" since we set CCACHE in anonymous function, and
d.getVar('CCACHE') works after "CCACHE ??=" which is set in bitbake.conf, so we
can't check whether CCACHE is set or not in anonymous function since it is
always set. Use CCACHE_DISABLE to disable it would be more clear.

(From OE-Core rev: b25271b65262f70d849a4861da216c9be6c54d53)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/ccache.bbclass

@@ -1,4 +1,14 @@
-CCACHE = "${@bb.utils.which(d.getVar('PATH'), 'ccache') and 'ccache '}"
+#
+# Usage:
+# - Enable ccache
+#   Add the following line to a conffile such as conf/local.conf:
+#   INHERIT += "ccache"
+#
+# - Disable ccache for a recipe
+#   Add the following line to the recipe if it can't be built with ccache:
+#   CCACHE_DISABLE = '1'
+#
+
 export CCACHE_DIR ?= "${TMPDIR}/ccache/${MULTIMACH_TARGET_SYS}/${PN}"
 
 # We need to stop ccache considering the current directory or the
@@ -7,5 +17,14 @@ export CCACHE_DIR ?= "${TMPDIR}/ccache/${MULTIMACH_TARGET_SYS}/${PN}"
 # ${PV} or ${PR} change.
 export CCACHE_NOHASHDIR ?= "1"
 
-DEPENDS_append_class-target = " ccache-native"
-DEPENDS[vardepvalueexclude] = " ccache-native"
+python() {
+    """
+    Enable ccache for the recipe
+    """
+    pn = d.getVar('PN')
+    # quilt-native doesn't need ccache since no c files
+    if not (pn in ('ccache-native', 'quilt-native') or
+            bb.utils.to_boolean(d.getVar('CCACHE_DISABLE'))):
+        d.appendVar('DEPENDS', ' ccache-native')
+        d.setVar('CCACHE', 'ccache ')
+}

meta/conf/bitbake.conf

@@ -492,7 +492,7 @@ HOSTTOOLS += " \
 HOSTTOOLS += "${@'ip ping ps scp ssh stty' if (bb.utils.contains_any('IMAGE_CLASSES', 'testimage testsdk', True, False, d) or any(x in (d.getVar("BBINCLUDED") or "") for x in ["testimage.bbclass", "testsdk.bbclass"])) else ''}"
 
 # Link to these if present
-HOSTTOOLS_NONFATAL += "aws ccache gcc-ar gpg ld.bfd ld.gold nc pigz sftp socat ssh sudo"
+HOSTTOOLS_NONFATAL += "aws gcc-ar gpg ld.bfd ld.gold nc pigz sftp socat ssh sudo"
 
 # Temporary add few more detected in bitbake world
 HOSTTOOLS_NONFATAL += "join nl size yes zcat"
@@ -504,10 +504,6 @@ HOSTTOOLS_NONFATAL += "bzr"
 HOSTTOOLS_NONFATAL += "scp"
 
 CCACHE ??= ""
-# ccache < 3.1.10 will create CCACHE_DIR on startup even if disabled, and
-# autogen sets HOME=/dev/null so in certain situations builds can fail.
-# Explicitly export CCACHE_DIR until we can assume ccache >3.1.10 on the host.
-export CCACHE_DIR ??= "${@os.getenv('HOME')}/.ccache"
 
 TOOLCHAIN_OPTIONS = " --sysroot=${STAGING_DIR_TARGET}"
 

meta/conf/layer.conf

@@ -49,7 +49,6 @@ SIGGEN_EXCLUDE_SAFE_RECIPE_DEPS += " \
   *->quilt-native \
   *->subversion-native \
   *->git-native \
-  *->ccache-native \
   *->icecc-create-env-native \
   gcc-cross-${TARGET_ARCH}->linux-libc-headers \
   ppp-dialin->ppp \

meta/lib/oe/utils.py

@@ -363,6 +363,9 @@ def host_gcc_version(d, taskcontextonly=False):
         return
 
     compiler = d.getVar("BUILD_CC")
+    # Get rid of ccache since it is not present when parsing.
+    if compiler.startswith('ccache '):
+        compiler = compiler[7:]
     try:
         env = os.environ.copy()
         env["PATH"] = d.getVar("PATH")