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

@@ -213,15 +213,36 @@ def pack(context: typer.Context, verbose: Verbose = False):
             f'Passing unrecognized arguments to `charmcraft pack`: {" ".join(context.args)}'
         )
     logger.info("Resolving dependencies")
-    if not pathlib.Path("requirements.txt").exists():
-        if not pathlib.Path("charmcraft.yaml").exists():
-            raise FileNotFoundError(
-                "requirements.txt not found. `cd` into the directory with charmcraft.yaml"
+    charmcraft_yaml = pathlib.Path("charmcraft.yaml")
+    poetry_lock_exists = pathlib.Path("poetry.lock").exists()
+    if not charmcraft_yaml.exists():
+        raise FileNotFoundError(
+            "charmcraft.yaml not found. `cd` into the directory with charmcraft.yaml"
+        )
+    if poetry_lock_exists:
+        # Convert subset of poetry.lock to requirements.txt
+        try:
+            subprocess.run(
+                [
+                    "poetry",
+                    "export",
+                    "--only",
+                    "main,charm-libs",
+                    "--output",
+                    "requirements.txt",
+                ],
+                check=True,
             )
-        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."
+        except FileNotFoundError:
+            raise Exception(
+                "poetry.lock detected but poetry not installed. 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 Exception("Failed to create requirements.txt from poetry.lock")
+    elif not pathlib.Path("requirements.txt").exists():
+        raise FileNotFoundError("requirements.txt not found")
     report_file = cache_directory / "report.json"
     subprocess.run(
         [
@@ -239,10 +260,11 @@ def pack(context: typer.Context, verbose: Verbose = False):
         stdout=None if state.verbose else subprocess.DEVNULL,
         check=True,
     )
+    if poetry_lock_exists:
+        pathlib.Path("requirements.txt").unlink()
     with open(report_file, "r") as file:
         report = json.load(file)
     dependencies = []
-    charmcraft_yaml = pathlib.Path("charmcraft.yaml")
     architecture = platform.machine()
     bases = get_charmcraft_yaml_bases(
         charmcraft_yaml=charmcraft_yaml, architecture=architecture

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 <carl.csaposs@canonical.com>"]
 readme = "README.md"