feat: HasFile event filter predicte

Signed-off-by: Lars Wirzenius <liw@liw.fi>

ci-broker.md

@@ -236,6 +236,8 @@ The Git repository must exist.
 ~~~scenario
 then directory reppy exists
 then directory reppy/.git exists
+then file reppy/file.dat exists
+then file reppy/foobar does not exist
 when I run, in reppy, git show
 then stdout matches regex ^commit
 ~~~
@@ -1230,6 +1232,53 @@ triggers:
 ~~~
 
 
+## Filter predicate `HasFile`
+
+_Want:_ We can allow an event if its commit contains a file or
+directory by this name.
+
+_Why:_ This is so that the user can choose a suitable adapter.
+
+~~~scenario
+given a Radicle node, with CI configured with broker.yaml and adapter dummy.sh
+given a Git repository xyzzy in the Radicle node
+
+given file config.yaml from filter-hasfile-missing.yaml
+when I run cibtool --db ci-broker.db event add --repo xyzzy --ref main --commit HEAD --kind branch-created
+when I run ./env.sh cib --config config.yaml queued
+when I run cibtool --db ci-broker.db run list --json
+then stdout doesn't contain "main"
+
+given file config.yaml from filter-hasfile.yaml
+when I run cibtool --db ci-broker.db event add --repo xyzzy --ref main --commit HEAD --kind branch-created
+when I run ./env.sh cib --config config.yaml queued
+when I run cibtool --db ci-broker.db run list --json
+then stdout contains "main"
+~~~
+
+~~~{#filter-hasfile.yaml .file .json}
+db: ci-broker.db
+adapters:
+  default:
+    command: ./adapter.sh
+triggers:
+  - adapter: default
+    filters:
+      - !HasFile "file.dat"
+~~~
+
+~~~{#filter-hasfile-missing.yaml .file .json}
+db: ci-broker.db
+adapters:
+  default:
+    command: ./adapter.sh
+triggers:
+  - adapter: default
+    filters:
+      - !HasFile "does-not-exist"
+~~~
+
+
 # Acceptance criteria for test tooling
 
 The event synthesizer is a helper to feed the CI broker node events in