cargo_common.bbclass: Support local github repos

Since disable network was added cargo configurations which reference git
repos fail as they attempt to fetch across the network as part of
do_compile, even if EXTRA_OECARGO_PATHS to add them as part of `paths`
is used, as this is documented as only working for packages which exist
in crates.io.

Add parsing of the SRC_URIs for git repos and include `[patch]` sections
to redirect to the checked out source repos which the bitbake fetcher
has already populated.

There are still cases which don't work - if you have multiple copies of
the same repo with different revisions, there's currently no way to
represent that and anything using a repo which has a virtual manifest
will fail to build (see https://github.com/rust-lang/cargo/issues/4934).

(From OE-Core rev: 684a8af41c5bb70db68e75f72bdc4c9b09630810)

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-recipe/cargo_common.bbclass

@@ -116,6 +116,36 @@ cargo_common_do_configure () {
 	EOF
 }
 
+python cargo_common_do_patch_paths() {
+    cargo_config = os.path.join(d.getVar("CARGO_HOME"), "config")
+    if not os.path.exists(cargo_config):
+        return
+
+    src_uri = (d.getVar('SRC_URI') or "").split()
+    if len(src_uri) == 0:
+        return
+
+    patches = dict()
+    workdir = d.getVar('WORKDIR')
+    fetcher = bb.fetch2.Fetch(src_uri, d)
+    for url in fetcher.urls:
+        ud = fetcher.ud[url]
+        if ud.type == 'git':
+            name = ud.parm.get('name')
+            destsuffix = ud.parm.get('destsuffix')
+            if name is not None and destsuffix is not None:
+                repo = '%s://%s%s' % (ud.proto, ud.host, ud.path)
+                path = '%s = { path = "%s" }' % (name, os.path.join(workdir, destsuffix))
+                patches.setdefault(repo, []).append(path)
+
+    with open(cargo_config, "a+") as config:
+        for k, v in patches.items():
+            print('\n[patch."%s"]' % k, file=config)
+            for name in v:
+                print(name, file=config)
+}
+do_configure[postfuncs] += "cargo_common_do_patch_paths"
+
 oe_cargo_fix_env () {
 	export CC="${RUST_TARGET_CC}"
 	export CXX="${RUST_TARGET_CXX}"