Add support for exporting poetry.lock to requirements.txt

tox build wrapper is being removed (https://warthogs.atlassian.net/browse/DPE-5046). e.g. canonical/mysql-router-k8s-operator#319

charmcraftcache/main.py

@@ -219,9 +219,30 @@ def pack(context: typer.Context, verbose: Verbose = False):
                 "requirements.txt not found. `cd` into the directory with charmcraft.yaml"
             )
         else:
-            raise FileNotFoundError(
-                "requirements.txt not found. Are you using a pack wrapper (e.g. `tox run -e build-dev`)? If so, call charmcraftcache via the wrapper."
-            )
+            # Convert subset of poetry.lock to requirements.txt
+            try:
+                subprocess.run(
+                    [
+                        "poetry",
+                        "export",
+                        "--only",
+                        "main,charm-libs",
+                        "--output",
+                        "requirements.txt",
+                    ],
+                    check=True,
+                )
+            except FileNotFoundError:
+                # poetry not installed
+                raise FileNotFoundError(
+                    "requirements.txt not found and poetry not installed. Are you using poetry.lock? If so, install poetry"
+                )
+            # TODO: add handling if poetry installed but poetry-plugin-export not installed
+            # (only applicable once https://github.com/python-poetry/poetry/pull/5980 merged)
+            except subprocess.CalledProcessError:
+                raise FileNotFoundError(
+                    "requirements.txt not found. Failed to create requirements.txt from poetry.lock"
+                )
     report_file = cache_directory / "report.json"
     subprocess.run(
         [

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "charmcraftcache"
-version = "0.3.8"
+version = "0.4.0"
 description = "Fast first-time builds for charmcraft"
 authors = ["Carl Csaposs <[email protected]>"]
 readme = "README.md"