Update cargo source to use source provenance

Author: joshua-zivkovic

src/buildstream_plugins/sources/cargo.py

@@ -74,6 +74,10 @@
 *version_type*, for which it reports the checksum of the archive as the *version*.
 
 The versions extracted from the Cargo.lock at tracking time are used to report the *guess_version*.
+
+Additional source info can be specified using the `provenance` field for each referenced crate as per
+`built-in source provenance documentation
+<https://docs.buildstream.build/master/buildstream.source.html#built-in-functionality>`_.
 """
 
 import json
@@ -125,13 +129,14 @@
 #    sha (str|None): The sha256 checksum of the downloaded crate
 #
 class Crate(SourceFetcher):
-    def __init__(self, cargo, name, version, sha=None):
+    def __init__(self, cargo, name, version, sha=None, provenance=None):
         super().__init__()
 
         self.cargo = cargo
         self.name = name
         self.version = str(version)
         self.sha = sha
+        self.provenance = provenance
         self.mark_download_url(cargo.url)
 
     ########################################################
@@ -159,7 +164,12 @@ def fetch(self, alias_override=None, **kwargs):
     def get_source_info(self):
         url, _ = self._get_url()
         return self.cargo.create_source_info(
-            url, SourceInfoMedium.REMOTE_FILE, SourceVersionType.SHA256, self.sha, version_guess=self.version
+            url,
+            SourceInfoMedium.REMOTE_FILE,
+            SourceVersionType.SHA256,
+            self.sha,
+            version_guess=self.version,
+            provenance_node=self.provenance,
         )
 
     ########################################################
@@ -368,6 +378,8 @@ class CargoSource(Source):
     # We need the Cargo.lock file to construct our ref at track time
     BST_REQUIRES_PREVIOUS_SOURCES_TRACK = True
 
+    BST_CUSTOM_SOURCE_PROVENANCE = True
+
     ########################################################
     #       Plugin/Source API method implementations       #
     ########################################################
@@ -513,6 +525,7 @@ def _parse_crates(self, refs):
                 crate.get_str("name"),
                 crate.get_str("version"),
                 sha=crate.get_str("sha", None),
+                provenance=crate.get_mapping("provenance", None),
             )
             for crate in refs
         ]