feat: add ability to read version from a file

README.md

@@ -29,6 +29,14 @@ Alternatively, it can read it from a **git tag**, set with a GitHub release or w
 $ git tag 0.1.0
 ```
 
+Alternatively, it can read a version from a static file (which may have been dynamically generated)
+```toml
+
+[tool.poetry-version-plugin]
+source = "version_file"
+filename = "src/mypackage/VERSION"
+```
+
 🚨 Consider this in the alpha stage. Read the warning below.
 
 ## When to use
@@ -112,6 +120,32 @@ Building my-awesome-package (0.1.3)
   - Built my-awesome-package-0.1.3-py3-none-any.whl
 ```
 
+### Set the version in a VERSION file
+
+With a `VERSION`` file, you can dynamically generate the file (as a step of the CI/CD pipeline for example) and read the file
+
+```python
+#__init__.py
+
+from functools import cache
+
+@cache
+def read_version_file() -> str:
+    """Simple style, read a file."""
+    try:
+        import pathlib
+        dir = pathlib.Path(__file__).parent.resolve()
+        return pathlib.Path(dir / "VERSION").read_text()
+    except Exception:
+        # Fall back in case the file was missing
+        return "0.0.0"
+
+__version__: str = read_version_file()
+
+```
+This provides a happy medium of both a static, or dynamically generated `VERSION` file that can be used
+in wider CI/CD build systems, and have both python, and poetry read the `VERSION` file.
+
 ## Version in `pyproject.toml`
 
 Currently (2021-05-24) Poetry requires a `version` configuration in the `pyproject.toml`, even if you use this plugin.
@@ -349,6 +383,14 @@ and
 source = "git-tag"
 ```
 
+or
+
+```toml
+[tool.poetry-version-plugin]
+source = "version_file"
+filename = "src/mypackage/VERSION"
+```
+
 let me know what alternative configuration would make more sense and be more intuitive to you.
 
 👍 The good news is, assuming you are building packages to then upload them to PyPI for your users to download and use them, the **worst that could happen** if something broke is that you wouldn't be able to build a new version until something is fixed or changed. But your users shouldn't be affected in any way.

poetry_version_plugin/plugin.py

@@ -113,11 +113,11 @@ def activate(self, poetry: Poetry, io: IO) -> None:
                     f"[{version_file_config}]. cannot extract dynamic version"
                 )
             else:
-                version = version_file.read_text()
+                version = version_file.read_text().strip()
                 io.write_line(
                     "<b>poetry-version-plugin</b>: Setting package "
-                    "dynamic version to __version__ "
-                    f"variable from __init__.py: <b>{version}</b>"
+                    f"dynamic version to value from {version_file}"
+                    f": <b>{version}</b>"
                 )
                 poetry.package._set_version(version)
                 return