[gnome-continuous-yocto/gnomeostree-3.28-rocko: 5180/8267] ccache: Disable CCACHE_HASHDIR by default

[Emmanuele Bassi <ebassi src gnome org>]

commit e987f620097df16c155303668e2b8093071fe75f
Author: Mike Crowe <mac mcrowe com>
Date:   Wed Mar 15 12:29:16 2017 +0000

    ccache: Disable CCACHE_HASHDIR by default
    
    As of ccache-3.3, ccache tries to ensure that the paths in the debug
    information are always correct. It does this by including the current
    directory in the hash if debug output is enabled. It includes support for
    detecting remapping via a single -fdebug-prefix-map argument uses the
    remapped directory in the hash instead.
    
    The DEBUG_PREFIX_MAP in bitbake.conf remaps the source directory, target
    sysroot and native sysroot separately which results in multiple
    -fdebug-prefix-map arguments. Although ccache passes all these arguments
    through to the compiler, it only enables the special behaviour described
    above if the last one matches the current directory. (See
    https://github.com/ccache/ccache/issues/163 )
    
    Even if ccache did correctly honour each of the remapping arguments, the
    hashes would still be different every time ${PV} or ${PR} change because
    the default DEBUG_PREFIX_MAP contains maps to paths including them.
    
    So it seems that for ccache to be of any use with this configuration,
    CCACHE_NOHASHDIR needs to be set.
    
    (From OE-Core rev: fb7a5cdcff19bb44a25a51e20de0440c1ebcc057)
    
    Signed-off-by: Mike Crowe <mac mcrowe com>
    Helped-by: Ross Burton <ross burton intel com>
    Signed-off-by: Ross Burton <ross burton intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 meta/classes/ccache.bbclass |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/meta/classes/ccache.bbclass b/meta/classes/ccache.bbclass
index 76c8828..9713fea 100644
--- a/meta/classes/ccache.bbclass
+++ b/meta/classes/ccache.bbclass
@@ -2,6 +2,12 @@ CCACHE = "${@bb.utils.which(d.getVar('PATH'), 'ccache') and 'ccache '}"
 export CCACHE_DIR ?= "${TMPDIR}/ccache/${MULTIMACH_HOST_SYS}/${PN}"
 CCACHE_DISABLE[unexport] = "1"
 
+# We need to stop ccache considering the current directory or the
+# debug-prefix-map target directory to be significant when calculating
+# its hash. Without this the cache would be invalidated every time
+# ${PV} or ${PR} change.
+export CCACHE_NOHASHDIR ?= "1"
+
 DEPENDS_append_class-target = " ccache-native"
 DEPENDS[vardepvalueexclude] = " ccache-native"