frontend: Log which elements resolved new keys

It can be difficult to pick out important information in all the messages,
so it's convenient to have classes of them collected into one place.

One such class of important information is when the cache key of an element changes,
such as when element's source is tracked or cached from a workspace,
since it can be important to know what the cache key is for that artifact.

Fixes issue #252

1 files changed, 15 insertions, 0 deletions

diff --git a/buildstream/_frontend/widget.py b/buildstream/_frontend/widget.py
index a07ae0c32..b5942b91e 100644
--- a/buildstream/_frontend/widget.py
+++ b/buildstream/_frontend/widget.py
@@ -335,6 +335,7 @@ class LogLine(Widget):
         self._indent = ' ' * indent
         self._log_lines = log_lines
         self._message_lines = message_lines
+        self._resolved_keys = None
 
         self._space_widget = Space(content_profile, format_profile)
         self._logfile_widget = LogFile(content_profile, format_profile, err_profile)
@@ -464,6 +465,13 @@ class LogLine(Widget):
         starttime = datetime.datetime.now()
         text = ''
 
+        assert self._resolved_keys is None
+        elements = set()
+        visited = {}
+        for element in pipeline.targets:
+            elements.update(element.dependencies(Scope.ALL, visited=visited))
+        self._resolved_keys = {element: element._get_cache_key() for element in elements}
+
         # Main invocation context
         text += '\n'
         text += self.content_profile.fmt("BuildStream Version {}\n".format(bst_version), bold=True)
@@ -537,6 +545,13 @@ class LogLine(Widget):
 
         text = ''
 
+        assert self._resolved_keys is not None
+        elements = sorted(e for (e, k) in self._resolved_keys.items() if k != e._get_cache_key())
+        if elements:
+            text += self.content_profile.fmt("Resolved key Summary\n", bold=True)
+            text += self.show_pipeline(elements, self._context.log_element_format)
+            text += "\n\n"
+
         if self._failure_messages:
             text += self.content_profile.fmt("Failure Summary\n", bold=True)
             values = OrderedDict()