TMP: convert extract into ValidatedInterface, and adopt constraint va…

…lidation

This is a demonstration how one existing command could adopt datalad-next's
parameter constraint validation. It changes the baseclass to next's
ValidatedInterface, and defines a validator with relevant parameter constraints:

Specifically, the constraints are:
- The provided datasets exists, or a dataset can be derived from the curdir
- The path points to an existing file (ref datalad#354)
- The extractorname is a string
- The extractorargs is a mapping of key-value pairs

This makes a dedicated check whether a file exists obsolete, and it could replace
the checks that check_dataset() does (provided an additional constraint option
in EnsureDataset() that allows to check for valid dataset IDs - I've created an
issue about this in datalad/datalad-next#272).

This change would introduce a dependency to datalad-next, and as parts of
this PR were only tested with yet unreleased branches of datalad-next,
it will not work right now unless you're on the right development version
of datalad-next.

datalad_metalad/extract.py

@@ -30,14 +30,22 @@
 from uuid import UUID
 
 from dataclasses import dataclass
-
+from datalad_next.commands import (
+    EnsureCommandParameterization,
+    ValidatedInterface,
+)
 from datalad.distribution.dataset import Dataset
-from datalad.distribution.dataset import (
-    datasetmethod,
-    EnsureDataset,
+from datalad.distribution.dataset import datasetmethod
+from datalad_next.constraints import (
+    EnsurePath,
+    EnsureStr,
+    EnsureMapping,
+    EnsureNone,
+    EnsureListOf,
+    NoConstraint,
 )
+from datalad_next.constraints.dataset import EnsureDataset
 from datalad.interface.base import (
-    Interface,
     build_doc,
     eval_results,
 )
@@ -54,10 +62,6 @@
     MetadataExtractorBase,
 )
 
-from datalad.support.constraints import (
-    EnsureNone,
-    EnsureStr,
-)
 from datalad.support.param import Parameter
 
 from dataladmetadatamodel.metadatapath import MetadataPath
@@ -91,7 +95,7 @@ class ExtractionArguments:
 
 
 @build_doc
-class Extract(Interface):
+class Extract(ValidatedInterface):
     """Run a metadata extractor on a dataset or file.
 
     This command distinguishes between dataset-level extraction and
@@ -131,6 +135,23 @@ class Extract(Interface):
     on the whether file-level- or dataset-level extraction is requested.
     """
 
+    # Define parameter constraints
+    extractorargs_constraints = EnsureMapping(key=EnsureStr(),
+                                    value=EnsureStr(),
+                                    delimiter='') | \
+                                EnsureListOf(item_constraint=NoConstraint(),
+                                    min_len=0)
+    _validator_ = EnsureCommandParameterization(
+        param_constraints=dict(
+            path=EnsurePath(lexists=True),
+            dataset=EnsureDataset(installed=True, purpose='meta-extract'),
+            extractor=EnsureStr(),
+            extractorargs=extractorargs_constraints,
+        ),
+        validate_defaults=("dataset",),
+        tailor_for_dataset=dict(path="dataset")
+    )
+
     result_renderer = "tailored"
 
     _examples_ = [
@@ -180,20 +201,20 @@ class Extract(Interface):
             specified.
             You might provide an absolute file path, but it has to contain
             the dataset path as prefix.""",
-            constraints=EnsureStr() | EnsureNone()),
+            ),
         dataset=Parameter(
             args=("-d", "--dataset"),
             doc="""Dataset to extract metadata from. If no dataset
             is given, the dataset is determined by the current work
             directory.""",
-            constraints=EnsureDataset() | EnsureNone()),
+            ),
         context=Parameter(
             args=("-c", "--context"),
             doc="""Context, a JSON-serialized dictionary that provides
             constant data which has been gathered before, so meta-extract
             will not have re-gather this data. Keys and values are strings.
             meta-extract will look for the following key: 'dataset_version'.""",
-            constraints=EnsureDataset() | EnsureNone()),
+            ),
         get_context=Parameter(
             args=("--get-context",),
             action="store_true",
@@ -219,7 +240,8 @@ class Extract(Interface):
             prevent interpretation of the key of the first extractor argument
             as path for a file-level extraction.""",
             nargs="*",
-            constraints=EnsureStr() | EnsureNone()))
+            )
+    )
 
     @staticmethod
     @datasetmethod(name="meta_extract")
@@ -247,7 +269,8 @@ def __call__(
                 if isinstance(context, str)
                 else context))
 
-        source_dataset = check_dataset(dataset or curdir, "extract metadata")
+        # dataset is a DatasetParameter from the parameter validation
+        source_dataset = dataset.ds
         source_dataset_version = context.get("dataset_version", None)
         if source_dataset_version is None:
             source_dataset_version = source_dataset.repo.get_hexsha()