meta-balena-rust: Provide crate fetcher for Yocto versions without it

The crate fetcher was introduced in bitbake in Kirkstone, before that
it was living in meta-rust.

We want to use the balena-rust layer across a wide variety of Yocto
versions so include the fetcher conditionally.

Signed-off-by: Alex Gonzalez <[email protected]>
Signed-off-by: Florin Sarbu <[email protected]>

meta-balena-rust/classes/cargo_common.bbclass

@@ -14,7 +14,14 @@
 ## is used by cargo.bbclass and Rust
 ##
 
+def set_crate_fetcher(d):
+    # Check to see whether bitbake has a crate fetcher (included in Kirkstone)
+    if not os.path.exists(os.path.join(d.getVar('TOPDIR'),'../layers/poky/bitbake/lib/bb/fetch2/crate.py')):
+        return "crate-fetch"
+    return ""
+
 # add crate fetch support
+inherit ${@set_crate_fetcher(d)}
 inherit rust-common
 
 # Where we download our registry and dependencies to

meta-balena-rust/classes/crate-fetch.bbclass

@@ -0,0 +1,28 @@
+#
+# crate-fetch class
+#
+# Registers 'crate' method for Bitbake fetch2.
+#
+# Adds support for following format in recipe SRC_URI:
+# crate://<packagename>/<version>
+#
+
+def import_crate(d):
+    import crate
+    if not getattr(crate, 'imported', False):
+        bb.fetch2.methods.append(crate.Crate())
+        crate.imported = True
+
+python crate_import_handler() {
+    import_crate(d)
+}
+
+addhandler crate_import_handler
+crate_import_handler[eventmask] = "bb.event.RecipePreFinalise"
+
+def crate_get_srcrev(d):
+    import_crate(d)
+    return bb.fetch2.get_srcrev(d)
+
+# Override SRCPV to make sure it imports the fetcher first
+SRCPV = "${@crate_get_srcrev(d)}"

meta-balena-rust/lib/crate.py

@@ -71,7 +71,7 @@ def _crate_urldata_init(self, ud, d):
         ud.parm['downloadfilename'] = "%s-%s.crate" % (name, version)
         ud.parm['name'] = name
 
-        logger.debug2("Fetching %s to %s" % (ud.url, ud.parm['downloadfilename']))
+        logger.debug(2, "Fetching %s to %s" % (ud.url, ud.parm['downloadfilename']))
 
     def unpack(self, ud, rootdir, d):
         """