Add dynamic base-revision

src/commands/set-parameters.yml

@@ -8,7 +8,8 @@ parameters:
     default: "main"
     description: >
       The revision to compare the current one against for the purpose
-      of determining changed files.
+      of determining changed files. Supports passing environment variables,
+      eg. $CIRCLE_BRANCH, or shell script evaluating to a string, eg. $(echo "dev").
   mapping:
     type: string
     default: ""

src/jobs/filter.yml

@@ -22,7 +22,8 @@ parameters:
     default: "main"
     description: >
       The revision to compare the current one against for the purpose
-      of determining changed files.
+      of determining changed files. Supports passing environment variables,
+      eg. $CIRCLE_BRANCH, or shell script evaluating to a string, eg. $(echo "dev").
   mapping:
     type: string
     default: ""
@@ -59,6 +60,10 @@ parameters:
     description: >
       Pick a specific cimg/python image variant:
       https://hub.docker.com/r/cimg/python/tags
+  before_set_params_script:
+      default: ""
+      description: Script to run before set-parameters step. Used to load custom environment variables.
+      type: string
 
 steps:
   - checkout
@@ -69,6 +74,14 @@ steps:
       steps:
         - attach_workspace:
             at: << parameters.workspace_path >>
+  - when:
+      condition:
+        not:
+          equal: ["", << parameters.before_set_params_script >>]
+      steps:
+        - run:
+            name: Before set-parameters script
+            command: << parameters.before_set_params_script >>
   - set-parameters:
       base-revision: << parameters.base-revision >>
       mapping: << parameters.mapping >>

src/scripts/create-parameters.py

@@ -23,6 +23,15 @@ def merge_base(base, head):
     capture_output=True
   ).stdout.decode('utf-8').strip()
 
+def eval_base(base):
+  if base.startswith('$'):
+    value = subprocess.run(
+      ['sh', '-c', f"echo {base}"],
+      capture_output=True
+    ).stdout.decode('utf-8').strip()
+    return 'main' if value == '' else value
+  return base
+
 def parent_commit():
   return subprocess.run(
     ['git', 'rev-parse', 'HEAD~1'],
@@ -112,6 +121,7 @@ def is_mapping_line(line: str) -> bool:
   return not (is_comment_line or is_empty_line)
 
 def create_parameters(output_path, config_path, head, base, mapping):
+  base = eval_base(base) # Evaluate base revision if it is an environment variable or script
   checkout(base)  # Checkout base revision to make sure it is available for comparison
   checkout(head)  # return to head commit
   base = merge_base(base, head)