build: derive the package version from git tags (setuptools-scm)

.github/workflows/tests.yml

@@ -41,6 +41,8 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0  # full history and tags, so setuptools-scm can derive the version
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
       with:

CHANGELOG.md

@@ -20,6 +20,7 @@ and versions follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - **`autoadaloc = <n>` is no longer discarded.** The value is the number of noise standard deviations a correlation must clear -- `nstd` inside the old code -- and it was the value of the `autoadaloc` keyword itself. Only `cutoff` was read, so a config saying `autoadaloc = 2` silently ran at the default of 0.3: no error, a different taper, a different posterior. `cutoff`, `nstd` and `autoadaloc` are all accepted, `cutoff` first. The default stays 0.3; it was 1 before the rewrite, so a block that gave `autoadaloc` as a bare flag with no value tapers differently than it used to.
 
 ### Breaking changes
+- **The package version comes from the latest git tag.** `pyproject.toml` hard-coded `version = "1.0"` while the repository was tagged `v0.2`, so the two disagreed and `pet version` reported a number no release carried. setuptools-scm now derives it at build time: a tagged commit gets the tag (`v0.2` -> `0.2`), later commits a development version such as `0.3.dev4+g196c956`. Nothing creates tags automatically; release by pushing one. Installed versions therefore drop from `1.0` to `0.3.devN` until the next tag. CI checks out the full history so the tags are visible, and a build without git metadata falls back to `0.0.0`.
 - **`localanalysis` and the parallel update are refused while the config is read.** Both worked before the update schemes were restructured, and both need the per-subset observation machinery (`_ext_obs`, `current_state`, `pert_preddata`) that the rewrite replaced with a single `DataLayout` built once at setup. `localanalysis` previously reached a branch that left the posterior equal to the prior while still reporting a misfit, and is no longer a registered strategy; naming either now raises `ConfigError` explaining why and naming `autoadaloc` and `distance_loc` as the alternatives. Reimplementing them on the new contract is tracked separately; `analysis_tools.parallel_upd` is left in place for the dormant GIES schemes that still call it.
 - **`conv_crit` in the `epf` section means a penalty magnitude, not a state change.** The outer EPF loop used to stop once no control moved more than `conv_crit` relative to its previous value; it now stops once `mean(epf['penalty']) / epf['r']` falls below it. The old test asked the wrong question: it reported success whenever the inner optimizer stalled, however badly the constraints were still violated, and refused to finish while a single control kept jittering. The default is still `1e-5`, so a config written for the old criterion loads unchanged, but the number now carries the units of the objective rather than being dimensionless — check it against your penalty's scale. The objective must write `penalty` into the `epf` dict it is handed; one that does not now raises `KeyError` instead of silently converging on the step size. Ported from upstream 5358e07 and 4b8d878.
 - `max_iter` in the `iteration` section is the number of update iterations. It used to count the prior forecast as iteration 0, so `max_iter: 5` performed four updates; the same config now performs five. To keep an existing run as it was, lower `max_iter` by one. The run table, the convergence message and the `assimilation_result_{i}` files already numbered updates from 1 with the prior as 0, and are unchanged.

pyproject.toml

@@ -1,10 +1,12 @@
 [build-system]
-requires = ["setuptools>=61.0", "wheel"]
+requires = ["setuptools>=64", "setuptools-scm>=8", "wheel"]
 build-backend = "setuptools.build_meta"
 
 [project]
 name = "PET"
-version = "1.0"
+# Derived from the latest git tag by setuptools-scm (v0.2 -> 0.2;
+# commits after it -> 0.3.devN+g<hash>). Release by pushing a tag.
+dynamic = ["version"]
 description = "Python Ensemble Toolbox"
 authors = [
   { name = "Data assimilation and optimization group" }
@@ -78,6 +80,10 @@ package-dir = {"" = "src"}
 [tool.setuptools.packages.find]
 where = ["src"]
 
+[tool.setuptools_scm]
+# Used when building without git metadata, e.g. from a source zip.
+fallback_version = "0.0.0"
+
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 markers = [