feat: requires-python (#536)

* feat: requires-python

refactor: updating to current proposal

fix: add tests and fix a few issues

docs: Update mostly from @joerick

docs: update README from readthedocs

* refactor: pull out config file reading

* fix: always assume highest Python patch version

* refactor: try new design

* refactor: function and bump MyPy to 0.800

* fix: tighten AST to call only, add docs

* fix: address review points from @joerick

bin/inspect_all_known_projects.py

@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+from __future__ import annotations
+
+import ast
+from pathlib import Path
+from typing import Iterator, Optional
+
+import click
+import yaml
+from ghapi.core import GhApi, HTTP404NotFoundError  # type: ignore
+from rich import print
+
+from cibuildwheel.projectfiles import Analyzer
+
+DIR = Path(__file__).parent.resolve()
+
+
+def parse(contents: str) -> Optional[str]:
+    try:
+        tree = ast.parse(contents)
+        analyzer = Analyzer()
+        analyzer.visit(tree)
+        return analyzer.requires_python or ""
+    except Exception:
+        return None
+
+
+def check_repo(name: str, contents: str) -> str:
+    s = f"  {name}: "
+    if name == "setup.py":
+        if "python_requires" not in contents:
+            s += "❌"
+        res = parse(contents)
+        if res is None:
+            s += "⚠️ "
+        elif res:
+            s += "✅ " + res
+        elif "python_requires" in contents:
+            s += "☑️"
+
+    elif name == "setup.cfg":
+        s += "✅" if "python_requires" in contents else "❌"
+    else:
+        s += "✅" if "requires-python" in contents else "❌"
+
+    return s
+
+
+class MaybeRemote:
+    def __init__(self, cached_file: Path | str, *, online: bool) -> None:
+        self.online = online
+        if self.online:
+            self.contents: dict[str, dict[str, Optional[str]]] = {
+                "setup.py": {},
+                "setup.cfg": {},
+                "pyproject.toml": {},
+            }
+        else:
+            with open(cached_file) as f:
+                self.contents = yaml.safe_load(f)
+
+    def get(self, repo: str, filename: str) -> Optional[str]:
+        if self.online:
+            try:
+                self.contents[filename][repo] = (
+                    GhApi(*repo.split("/")).get_content(filename).decode()
+                )
+            except HTTP404NotFoundError:
+                self.contents[filename][repo] = None
+            return self.contents[filename][repo]
+        elif repo in self.contents[filename]:
+            return self.contents[filename][repo]
+        else:
+            raise RuntimeError(
+                f"Trying to access {repo}:{filename} and not in cache, rebuild cache"
+            )
+
+    def save(self, filename: Path | str) -> None:
+        with open(filename, "w") as f:
+            yaml.safe_dump(self.contents, f, default_flow_style=False)
+
+    def on_each(self, repos: list[str]) -> Iterator[tuple[str, str, Optional[str]]]:
+        for repo in repos:
+            print(f"[bold]{repo}:")
+            for filename in sorted(self.contents, reverse=True):
+                yield repo, filename, self.get(repo, filename)
+
+
+@click.command()
+@click.option("--online", is_flag=True, help="Remember to set GITHUB_TOKEN")
+def main(online: bool) -> None:
+    with open(DIR / "../docs/data/projects.yml") as f:
+        known = yaml.safe_load(f)
+
+    repos = [x["gh"] for x in known]
+
+    ghinfo = MaybeRemote("all_known_setup.yaml", online=online)
+
+    for _, filename, contents in ghinfo.on_each(repos):
+        if contents is None:
+            print(f"[red]  {filename}: Not found")
+        else:
+            print(check_repo(filename, contents))
+
+    if online:
+        ghinfo.save("all_known_setup.yaml")
+
+
+if __name__ == "__main__":
+    main()