_frontend/widget: Add artifact-cas-digest show format

This adds the artifact-cas-digest format string to the show command,
allowing to show the CAS digest of the built artifact.

Author: Adrien Plazas

man/bst-show.1

@@ -45,6 +45,7 @@ Show elements in the pipeline
         %{deps}           A list of all dependencies
         %{build-deps}     A list of build dependencies
         %{runtime-deps}   A list of runtime dependencies
+        %{artifact-cas-digest} The CAS digest of the built artifact
 .PP
     The value of the %{symbol} without the leading '%' character is understood
     as a pythonic formatting string, so python formatting features apply,

src/buildstream/_frontend/cli.py

@@ -613,6 +613,7 @@ def show(app, elements, deps, except_, order, format_):
         %{deps}           A list of all dependencies
         %{build-deps}     A list of build dependencies
         %{runtime-deps}   A list of runtime dependencies
+        %{artifact-cas-digest} The CAS digest of the built artifact
 
     The value of the %{symbol} without the leading '%' character is understood
     as a pythonic formatting string, so python formatting features apply,
@@ -638,7 +639,8 @@ def show(app, elements, deps, except_, order, format_):
         state_match = re.search(r"%(\{(state)[^%]*?\})", format_)
         key_match = re.search(r"%(\{(key)[^%]*?\})", format_)
         full_key_match = re.search(r"%(\{(full-key)[^%]*?\})", format_)
-        need_state = bool(state_match or key_match or full_key_match)
+        artifact_cas_digest_match = re.search(r"%(\{(artifact-cas-digest)[^%]*?\})", format_)
+        need_state = bool(state_match or key_match or full_key_match or artifact_cas_digest_match)
 
         if not elements:
             elements = app.project.get_default_targets()

src/buildstream/_frontend/widget.py

@@ -437,6 +437,21 @@ def show_pipeline(self, dependencies, format_):
                 runtime_deps = [e._get_full_name() for e in element._dependencies(_Scope.RUN, recurse=False)]
                 line = p.fmt_subst(line, "runtime-deps", _yaml.roundtrip_dump_string(runtime_deps).rstrip("\n"))
 
+            # Artifact CAS Digest
+            if "%{artifact-cas-digest" in format_:
+                artifact = element._get_artifact()
+                if not artifact.query_cache():
+                    artifact = None
+                if artifact is not None:
+                    artifact_files = artifact.get_files()
+                    # We call the private CasBasedDirectory._get_digest() for
+                    # the moment, we should make it public on Directory.
+                    artifact_digest = artifact_files._get_digest()
+                    formated_artifact_digest = "{}/{}".format(artifact_digest.hash, artifact_digest.size_bytes)
+                    line = p.fmt_subst(line, "artifact-cas-digest", formated_artifact_digest)
+                else:
+                    line = p.fmt_subst(line, "artifact-cas-digest", "(no artifact CAS digest)", fg="yellow")
+
             report += line + "\n"
 
         return report.rstrip("\n")

tests/frontend/show.py

@@ -438,8 +438,9 @@ def setup_test():
         ("%{deps}", "- import-dev.bst\n- import-links.bst\n- import-bin.bst"),
         ("%{build-deps}", "- import-dev.bst\n- import-links.bst"),
         ("%{runtime-deps}", "- import-links.bst\n- import-bin.bst"),
+        ("%{artifact-cas-digest}", "(no artifact CAS digest)"),
     ],
-    ids=["deps", "build-deps", "runtime-deps"],
+    ids=["deps", "build-deps", "runtime-deps", "artifact-cas-digest"],
 )
 def test_format_deps(cli, datafiles, dep_kind, expected_deps):
     project = str(datafiles)