Nested reusable workflows and matrices: parsing error

[trueneu]

Hey.
I'm using 2-level nested re-usable workflows, so the main workflow M calls workflow A that calls another workflow B. M runs a job that forms a JSON that's passed as a string to A. A then has two jobs: first, JOB1, calls B with matrix strategy, reading matrix with fromJson; second, JOB2, has some explicit steps defined, also with matrix strategy from the exact same matrix. JOB2 needs JOB1.
Now the funny thing is, as soon as I introduce JOB1 into the workflow A, it fails claiming it can't render the strategy (specific details ommitted):

Error when evaluating 'strategy' for job 'JOB1'. path-to-yml (Line: X, Col: Y): Error parsing fromJson,path-to-yml (Line: X, Col: Y): Error reading JToken from JsonReader. Path '', line 0, position 0.,path-to-yml (Line: X, Col: Y): Unexpected type of value '', expected type: Mapping.

So from the error message it seems that the matrix string is empty and can't be parsed. However the debug output (just echoing the string) in a separate job shows it's a perfectly valid JSON. As soon as I comment out JOB1, JOB2 runs perfectly with literally no other changes. If I change the aforementioned debug job to also use the matrix strategy and make it needed for JOB2, everything runs once again. If I call workflow B directly from workflow M, it also works.

I can't really show a minimal reproducible example right now, but perhaps the description is enough. If it helps, I'll add it later.

UPD: please see the minimal reproducible example here: https://github.com/orgs/community/discussions/32023#discussioncomment-3561655

[airtower-luna]

I can't really show a minimal reproducible example right now, but perhaps the description is enough.

Probably not, because the exact structure of both the JSON and how the matrix is initialized from is critical here. I've seen enough people use the approach, so most likely something is slightly off.

[trueneu]

@airtower-luna

Please take a look here: https://github.com/trueneu/github-actions-nested-workflows

In case it's more convenient for the conversation, here are the files:

main.yml:

name: main workflow
on:
  push:
    branches:
      - '**'

jobs:
  matrix-gen:
    name: generate matrix
    runs-on: ubuntu-latest
    outputs:
      output-matrix: ${{ steps.generate.outputs.output-matrix }}
    steps:
      - run: |
          echo -n "::set-output name=output-matrix::{\"include\": [{\"key\": \"value1\"}, {\"key\": \"value2\"}]}"
        id: generate

  debug-output-main:
    runs-on: ubuntu-latest
    needs:
      - matrix-gen
    steps:
      - run: |
          echo ${{ needs.matrix-gen.outputs.output-matrix }}

  call-A:
    needs:
      - matrix-gen
    uses: ./.github/workflows/A.yml
    with:
      matrix-input: ${{ needs.matrix-gen.outputs.output-matrix }}

  call-B-from-main:
    uses: ./.github/workflows/B.yml
    needs:
      - matrix-gen
    strategy:
      matrix: ${{ fromJson(needs.matrix-gen.outputs.output-matrix) }}
    with:
      value: ${{ matrix.key }}

A.yml:

name: reusable workflow A
on:
  workflow_call:
    inputs:
      matrix-input:
        type: string
        required: true

jobs:
  debug-output-A:
    name: debug output
    runs-on: ubuntu-latest
    strategy:
      matrix: ${{ fromJson(inputs.matrix-input) }}
    steps:
      - run: |
          echo '${{ matrix.key }}'

  call-B-plain:
    uses: ./.github/workflows/B.yml
    with:
      value: 'arbitrary string'

  call-B-with-matrix:
    uses: ./.github/workflows/B.yml
    strategy:
      matrix: ${{ fromJson(inputs.matrix-input) }}
    with:
      value: ${{ matrix.key }}

B.yml:

name: reusable workflow B
on:
  workflow_call:
    inputs:
      value:
        type: string
        required: true

jobs:
  debug-output-B:
    name: debug output
    runs-on: ubuntu-latest
    steps:
      - run: |
          echo '${{ inputs.value }}'

[trueneu]

call-B-from-main will succeed, but call-B-with-matrix will fail to render the strategy.

[airtower-luna]

The only difference I can spot there is the use of the inputs context in A.yml, instead of needs in main.yml. I assume that means inputs isn't available for defining a matrix.

I'm not sure if that's intentional, the documentation on inputs says:

You can access this context from any job or step in a workflow.

Personally I'd consider matrix part of a job, but maybe they mean each matrix instance? They are separate jobs in the UI after all… 😕

You can try to report a bug, and maybe a staff member see will this thread.

[trueneu]

That would hold, but if only the other job using inputs to define the matrix wouldn't work either. It seems like an inconsistency or discrepancy of some sort. I will report a bug, thank you.

[trueneu]

For anybody interested, here's the ticket - https://support.github.com/ticket/personal/0/1776040

[ShutdownRepo]

Thank you @trueneu 🙏

[trueneu]

@ShutdownRepo I was told that it's been reproduced and forwarded to the Engineering Team.

[trueneu]

Hey @ShutdownRepo , I've got the message that the behaviour was fixed, can you confirm?

[ShutdownRepo]

Hey @ShutdownRepo , I've got the message that the behaviour was fixed, can you confirm?

Wow indeed, what a great news! Tested and confirmed https://github.com/ShutdownRepo/github-actions-nested-workflows/actions/runs/4383907692

[trueneu]

Great!