Don't re-download installed models (#12188)

* Don't re-download installed models

When downloading a model, this checks if the same version of the same
model is already installed. If it is then the download is skipped.

This is necessary because pip uses the final download URL for its
caching feature, but because of the way models are hosted on Github,
their URLs change every few minutes.

* Use importlib instead of meta.json

* Use get_package_version

* Add untested, disabled test

---------

Co-authored-by: Adriane Boyd <adrianeboyd@gmail.com>

.github/azure-steps.yml

@@ -62,6 +62,11 @@ steps:
 #  - script: |
 #      python -W error -c "import ca_core_news_sm; nlp = ca_core_news_sm.load(); doc=nlp('test')"
 #    displayName: 'Test no warnings on load (#11713)'
+#    condition: eq(variables['python_version'], '3.8')
+#
+#  - script: |
+#      python -m spacy download ca_core_news_sm 2>&1 | grep -q skipping
+#    displayName: 'Test skip re-download (#12188)'
 #    condition: eq(variables['python_version'], '3.8')
 
   - script: |

spacy/cli/download.py

@@ -7,7 +7,8 @@ import typer
 from ._util import app, Arg, Opt, WHEEL_SUFFIX, SDIST_SUFFIX
 from .. import about
 from ..util import is_package, get_minor_version, run_command
-from ..util import is_prerelease_version
+from ..util import is_prerelease_version, get_installed_models
+from ..util import get_package_version
 
 
 @app.command(
@@ -63,6 +64,14 @@ def download(
         compatibility = get_compatibility()
         version = get_version(model_name, compatibility)
 
+    # If we already have this version installed, skip downloading
+    installed = get_installed_models()
+    if model_name in installed:
+        installed_version = get_package_version(model_name)
+        if installed_version == version:
+            msg.warn(f"{model_name} v{version} already installed, skipping")
+            return
+
     filename = get_model_filename(model_name, version, sdist)
 
     download_model(filename, pip_args)