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.
# 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 Novus Examples 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)Related files
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- yamlYAML Block Scalars and Chomping IndicatorsEvery block-scalar variation in one file: literal and folded styles, all three chomping indicators, an explicit indentation indicator, a folded block with a paragraph break, and an embedded shell-shaped script whose own indentation must survive.
- yamlYAML Bounded Anchor ReuseNested anchor reuse kept deliberately small: two anchors, six references, thirty-one expanded nodes. It is here to test alias resolution and expansion accounting on a safe input, and is explicitly not a billion-laughs expansion bomb.
- yamlYAML Directives and CommentsA two-document stream where each document declares its own %YAML directive and the second adds a %TAG handle used by a local tag. Comments appear in every position they are legal, and every one of them is lost by a non-round-tripping loader.
- yamlYAML Duplicate KeysDuplicate keys at three nesting levels, including a duplicated top-level sequence. The spec forbids them; most loaders keep the last silently, a few keep the first, and strict linters reject the document. The file publishes the last-wins answer.
- yamlYAML Explicit and Local TagsExplicit tags across the standard set — !!str, !!float, !!int, !!bool, !!null, !!binary, !!timestamp, !!omap, !!set — alongside two application-local ! tags. CI dialects use local tags in the wild, so a pipeline parser has to decide whether to reject, ignore, or resolve them.
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