adr step output and conclusion (#274)

docs/adrs/0274-step-outcome-and-conclusion.md

@@ -0,0 +1,62 @@
+# ADR 0274: Step outcome and conclusion
+
+**Date**: 2020-01-13
+
+**Status**: Accepted
+
+## Context
+
+This ADR proposes adding `steps.<id>.outcome` and `steps.<id>.conclusion` to the steps context.
+
+This allows downstream a step to run based on whether a previous step succeeded or failed.
+
+Reminder, currently the steps contains `steps.<id>.outputs`.
+
+## Decision
+
+For steps that have completed, populate `steps.<id>.outcome` and `steps.<id>.conclusion` with one of the following values:
+
+- `success`
+- `failure`
+- `cancelled`
+- `skipped`
+
+When a continue-on-error step fails, the outcome will be `failure` even though the final conclusion is `success`.
+
+### Example
+
+```yaml
+steps:
+
+  - id: experimental
+    continue-on-error: true
+    run: ./build.sh experimental
+
+  - if: ${{ steps.experimental.outcome == 'success' }}
+    run: ./publish.sh experimental
+```
+
+### Terminology
+
+The runs API uses the term `conclusion`.
+
+Therefore we use a different term `outcome` for the value prior to continue-on-error.
+
+The following is a snippet from the runs API response payload:
+
+```json
+      "steps": [
+        {
+          "name": "Set up job",
+          "status": "completed",
+          "conclusion": "success",
+          "number": 1,
+          "started_at": "2020-01-09T11:06:16.000-05:00",
+          "completed_at": "2020-01-09T11:06:18.000-05:00"
+        },
+```
+
+## Consequences
+
+- Update runner
+- Update [docs](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/contexts-and-expression-syntax-for-github-actions#steps-context)