Aggregate the _metadata.yml Inheritance Chain

Collects every _metadata.yml from the Quarto project root down to path and merges them, so that a deeper folder overrides a shallower one. This is the inheritance chain setup_mesos() writes — project, then wave, then chapter — and the mechanism behind the parameters object that generated chapters use.

Quarto's own params cannot provide this: it resolves to the individual .qmd file's YAML and carries no inheritance.

Usage

aggregate_metadata_yml(path = ".")

Arguments

path

Folder to resolve the chain for

scalar<character> // default: "." (optional)

The folder to treat as the deepest level of the chain, normally the one holding the .qmd being rendered. The default is correct at render time: Quarto executes a document with the working directory set to that document's own folder unless the project sets execute-dir: project.

Value

A named list of the merged YAML, empty if nothing was found. The params element is the part generated chapters use.

Details

The walk is bounded by the Quarto project root — the nearest ancestor of path holding a _quarto.yml or a _quarto.yaml. A _metadata.yml above that root is not read. When no project file is found anywhere above path, only path itself is read, so the walk can never escape into unrelated folders.

A folder without a _metadata.yml does not end the walk; it simply contributes nothing. Neither does an empty or non-mapping one, which is what setup_mesos() writes at intermediate levels.

Both _metadata.yml and _metadata.yaml are read. In the unlikely event that one folder holds both, _metadata.yml is merged first, so _metadata.yaml wins.

Merging is utils::modifyList(), which descends into nested lists: a deeper folder overriding params$mesos_group leaves its siblings under params intact.

Examples

project <- fs::path(tempdir(), "example_project")
fs::dir_create(fs::path(project, "Chapter"))
cat("project:\n  type: website\n", file = fs::path(project, "_quarto.yml"))
yaml::write_yaml(
  list(params = list(save = TRUE, wave = "2025")),
  file = fs::path(project, "_metadata.yml")
)
yaml::write_yaml(
  list(params = list(wave = "2026")),
  file = fs::path(project, "Chapter", "_metadata.yml")
)

# The deeper `wave` wins; `save` is inherited from the project level.
aggregate_metadata_yml(fs::path(project, "Chapter"))$params
#> $save
#> [1] TRUE
#> 
#> $wave
#> [1] "2026"
#>