I didn't get time yesterday or today to look into this, and I'll be busy for the next couple days, but I think this is important and will try to investigate and update if possible.

Just took a look and confirmed that path filters don't work quite as we want them to; uploaded https://crrev.com/c/1023595.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/d623320fabd9be1a62e3cb1414e67e6bb71a0c10

commit d623320fabd9be1a62e3cb1414e67e6bb71a0c10
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Mon Apr 23 17:21:55 2018

Change PathFilter matching to apply only to file basenames

Path filters are matched against paths with filepath.Match;
this matching works like Bash glob matching, so
foo/*.md matches "foo/bar.md", but "*.md" does not.

But, for analyzer path filters, we mainly want to use path
filters to be able to express "this analyzer applies to a
certain type of file.".

This CL changes the behavior so that "*.ext" matches files
with that extension regardless of directory nesting.

Bug:  832920 
Change-Id: I3c7456303fcd5ff4bff2bd6e1ba949bd9aa1f53a
Reviewed-on: https://chromium-review.googlesource.com/1023595
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>

[modify] https://crrev.com/d623320fabd9be1a62e3cb1414e67e6bb71a0c10/go/src/infra/tricium/api/v1/pb.discovery.go
[modify] https://crrev.com/d623320fabd9be1a62e3cb1414e67e6bb71a0c10/go/src/infra/tricium/api/v1/function.pb.go
[modify] https://crrev.com/d623320fabd9be1a62e3cb1414e67e6bb71a0c10/go/src/infra/tricium/appengine/common/config/generate_test.go
[modify] https://crrev.com/d623320fabd9be1a62e3cb1414e67e6bb71a0c10/go/src/infra/tricium/api/v1/function.proto
[modify] https://crrev.com/d623320fabd9be1a62e3cb1414e67e6bb71a0c10/go/src/infra/tricium/appengine/common/config/generate.go

After that change, it looks like the copyright analyzer is running (at least in the "playground" repo: https://chromium-review.googlesource.com/c/playground/gerrit-tricium/+/1025141

It's still not running in the Fuchsia repos: https://fuchsia-review.googlesource.com/c/garnet/+/146924

Nevermind, it is: https://fuchsia-review.googlesource.com/c/zircon/+/146315

Alright, thanks for confirming :-)

Note, it wasn't run on https://fuchsia-review.googlesource.com/c/garnet/+/146924 because that change doesn't contain any paths that match the path filters. (Maybe a few more file extensions could potentially be added to the path filters, e.g. "*.go".)