Expected a mapping or list of mappings for merging, but > found scalar

[James Carter]

I really don't get why this simplistic bitbucket pipeline is throwing the yaml syntax error:

There is a YAML syntax error in your bitbucket-pipelines.yml at [line 3, column 13]. Expected a mapping or list of mappings for merging, but found scalar

definitions:
  steps:
    - step: &prep_base_images
      name: Docker compose build base images
      image: docker:latest
      deployment: test
      script:
        - echo "hello world"

# Actual pipelines
# ==============================================================================
pipelines:
  branches:
    BLAH-137-backend-and-cicd-update:
      - step:
          <<: *prep_base_images
          deployment: development

Does anyone have any ideas?

[Aron Gombas _Midori_ · Accepted solution]

My first wild guess would be indentation.

Instead of:

definitions:
  steps:
    - step: &prep_base_images
      name: Docker compose build base images

Try:

definitions:
  steps:
    - step: &prep_base_images
        name: Docker compose build base images

Can you see that "name" was indented?

I am not sure if it is required or only a best practice in this file, but if it is required, then it could be the cause.

[Ian Klek]

This saved me, thanks! sadly bitbuckets yml validation feature was pathetic and always stated it was valid!