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.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>

1 files changed, 22 insertions, 3 deletions

diff --git a/meta/classes/ccache.bbclass b/meta/classes/ccache.bbclass
index 960902065c4..59e10226783 100644
--- a/meta/classes/ccache.bbclass
+++ b/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 ')
+}