Metadata hooks should run even when `project.dynamic` is empty

[bilelomrani1]

Problem

Metadata hooks only run when project.dynamic is non-empty. This is a problem for plugins that need to modify existing static metadata rather than populate dynamic fields.

In hatchling/metadata/core.py:

if metadata.dynamic:
    for metadata_hook in metadata_hooks.values():
        metadata_hook.update(self.core_raw_metadata)

Even if [tool.hatch.metadata.hooks.my-plugin] is configured, the hook never runs unless project.dynamic has at least one entry. This came up in #2038 where users found this requirement counter-intuitive.

Use case

Consider a plugin that rewrites workspace dependency versions at build time:

[project]
name = "my-client"
dependencies = ["my-core"]  # workspace dependency, no version

[tool.uv.sources]
my-core = { workspace = true }

[tool.hatch.metadata.hooks.my-plugin]
...

The plugin reads dependencies from [project].dependencies, looks up my-core's version from the lockfile, and outputs my-core>=1.2.3 in the built wheel.

Keeping dependencies in [project].dependencies is essential. This is the standard location per PEP 621, and the entire Python tooling ecosystem expects dependencies there. Moving them elsewhere breaks interoperability with many tools, for instance:

• Dependabot can't detect dependencies outside [project].dependencies (no custom location support, also here)
• Renovate needs custom regex managers for non-standard locations
• pip-audit and safety won't scan dependencies in non-standard locations
• deptry can't verify imports match declared dependencies
• Monorepo tools like Moon, Nx, etc. use static analysis to build internal dependency graphs, non-standard locations break this

Current workarounds

Dummy PEP 621 field:

[project]
dynamic = ["license-files"]  # not actually dynamic, just triggers hooks

Misleading, but passes schema validation.

Arbitrary string (used by hatch-dependency-coversion), from their official docs:

[project]
# the dynamic entry must be present and the array must not be empty, otherwise hatch
# will not invoke the plugin. however, something in dynamic cannot be in the rest of
# the metadata, and only top-level keys can appear here - so if you did
# dynamic = ['dependencies'], then it (a) would not be true since it's not all the
# dependencies, just the versions of some of them and (b) you couldn't have a
# dependencies entry in the project table. so put an arbitrary string here, and the
# name of the plugin is as good an arbitrary string as any.
dynamic = ['dependency-coversioning']

This works but fails schema validation in editors like Even Better TOML, and looks like a hack.

Declare dependencies as dynamic (used by uv-dynamic-versioning):

[project]
dynamic = ["dependencies"]

[tool.hatch.metadata.hooks.uv-dynamic-versioning]
dependencies = ["my-core=={{ version }}"]

This moves dependencies out of [project].dependencies entirely, which breaks all the tooling mentioned above.

Proposal

Run metadata hooks whenever [tool.hatch.metadata.hooks.*] is configured, regardless of project.dynamic. The existing validation that prevents hooks from adding undeclared fields would still apply, this just changes whether hooks run.