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YAML Merge Keys and Precedence

Merge keys with their full precedence rules: local keys beat merged ones, and in a merge sequence the earlier alias wins. The file publishes the expected merged values, and a strict YAML 1.2 loader produces none of them because 1.2 dropped << from the core schema.

Config parsingEncoding detectionEditor testing
Preview, first 38 linesyaml
# Merge keys. `<<` is a YAML 1.1 type (tag:yaml.org,2002:merge) that YAML 1.2 dropped from the
# core schema. A 1.1 loader merges the aliased mapping into the current one; a strict 1.2 loader
# treats `<<` as an ordinary key whose value happens to be an alias, so the merge never happens
# and every job silently loses its inherited settings.
#
# Precedence: keys written in the mapping itself WIN over merged keys, and in a merge sequence
# the EARLIER alias wins over later ones.
.defaults: &defaults
  image: registry.example.invalid/ci/runner:1.4
  retries: 2
  timeout: 30

.linux: &linux
  os: linux
  arch: amd64
  timeout: 600

build:
  <<: *defaults
  script: make build

test:
  <<: [*defaults, *linux]
  retries: 5
  script: make test

deploy:
  <<: *defaults
  timeout: 900
  script: make deploy

expected:
  build_timeout: 30
  test_timeout: 30
  test_retries: 5
  test_os: linux
  deploy_timeout: 900

Specifications

Merge Keys
3
Merge Sequences
1
Yaml11 Feature
true
Yaml12 Core Schema
<< is an ordinary key
Expected Test Timeout
30
Expected Test Retries
5

Testing contract

Expected to pass
Scenario
Apply YAML merge-key semantics, including a merge sequence with conflicting keys
Expected result
test.timeout resolves to 30 (the earlier alias wins over *linux's 600) and test.retries to 5 (the local key wins over the merged 2)

What is a .yaml file?

YAML (YAML Ain't Markup Language) is a human-readable data-serialization format using indentation, key-value pairs, and lists, and is a superset of JSON. It supports comments, anchors, and multiple documents per file, favoring readability for configuration. Its indentation sensitivity makes it error-prone to hand-edit.

How to use this file

Use an example YAML file to test config parsers, indentation and anchor handling, multi-document streams, and safe-loading to avoid arbitrary object construction.

How to use this file for testing

“YAML Merge Keys and Precedence” is a deterministic Testaroo fixture for Config parsing, Encoding detection, Editor testing. TOML and INI configuration files with nested sections and typed values, for testing config parsers and loaders.

Documented properties for this file: YAML · 915 bytes. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.

Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such, expect parsers to fail loudly rather than silently accept them.

Pipeline and infrastructure fixtures are inert configuration: steps reference fictional images and scripts, and nothing here executes. Run your linter, schema validator, migrator, or policy engine against them, and expect the deprecated-syntax and intentionally invalid variants to be rejected.

Point your config loader at the file and assert it reads the documented sections and typed values, including any deliberately-tricky nesting or comments.

Code examples

import yaml  # pip install pyyaml

with open("merge-keys.yaml") as f:
    data = yaml.safe_load(f)
print(data)

Generated by generation/pipelines.py. Free for any use, no attribution required, license.

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