classes/cargo_common: ensure B is clean

The cargo class defaults to out-of-tree builds in WORKDIR/build, but
at no point was that directory cleaned.  This causes problems with the
rust standard library recipe (libstd-rs) which installs manually with cp,
so rebuilds can be contaminated with the contents of previous builds.

I believe that post-release we should switch cargo.bbclass to mandating
out-of-tree builds to reduce the complexity, but for now in out-of-tree
builds we can just delete the ${B}/target directory.

Note that we use ${B}/target because there at least were reasons to use
that name[1], it is unclear if these limitations still hold. We can't
simply clean ${B} because that will break recipes that use cargo and
something else to build, for example librsvg.

[1] https://github.com/rust-lang/cargo/pull/1657

(From OE-Core rev: 1452ac7a44196454a52f3f6d883290ddcccfd3f8)

(From OE-Core rev: 9d9ce457630ea7403ffe7028e3370647db0b83fa)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/meta/classes-recipe/cargo_common.bbclass b/meta/classes-recipe/cargo_common.bbclass
index c9eb2d09a5..bc44ad7918 100644
--- a/meta/classes-recipe/cargo_common.bbclass
+++ b/meta/classes-recipe/cargo_common.bbclass
@@ -110,6 +110,10 @@ cargo_common_do_configure () {
         # Put build output in build directory preferred by bitbake instead of
         # inside source directory unless they are the same
         if [ "${B}" != "${S}" ]; then
+                # We should consider mandating out-of-tree builds and just using [cleandirs]
+                rm -rf ${B}/target
+                mkdir -p ${B}
+
                 cat <<- EOF >> ${CARGO_HOME}/config.toml
 
                 [build]