Fix deps with ~= version specifier treated as local paths (#3726)

## Summary
- Fix `deps = pre-commit ~= 4` being treated as a local path instead of
an invalid requirement
- Root cause: `packaging.Requirement()` rejects `~=` with single-segment
versions (PEP 440 requires 2+ segments), then tox's fallback treats the
`~` as a tilde home directory path
- Fix: detect PEP 440 version specifier operators before path detection,
keep the string as-is for pip to give a clear error

Closes #3447

## Test plan
- [x] Added parametrized test for `pre-commit ~= 4` and `pre-commit~=4`
- [x] All 104 req file tests pass
- [x] All 49 pip install tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

docs/changelog/3447.bugfix.rst

@@ -0,0 +1,2 @@
+Fix ``deps`` entries with ``~=`` version specifier being incorrectly treated as local paths instead of being passed
+through to pip - by :user:`Fridayai700`.

src/tox/tox_env/python/pip/req/file.py

@@ -27,6 +27,7 @@
 # https://www.python.org/dev/peps/pep-0508/#extras
 _EXTRA_PATH = re.compile(r"(.*)\[([-._,\sa-zA-Z0-9]*)]")
 _EXTRA_ELEMENT = re.compile(r"[a-zA-Z0-9]*[-._a-zA-Z0-9]")
+_VERSION_SPECIFIER = re.compile(r"[><=!~]=|===?|[><]")
 ReqFileLines = Iterator[tuple[int, str]]
 
 DEFAULT_INDEX_URL = "https://pypi.org/simple"
@@ -40,6 +41,8 @@ def __init__(self, req: str, options: dict[str, Any], from_file: str, lineno: in
         except InvalidRequirement:
             if is_url(req) or any(req.startswith(f"{v}+") and is_url(req[len(v) + 1 :]) for v in VCS):
                 self._requirement = req
+            elif _VERSION_SPECIFIER.search(req):
+                self._requirement = req  # invalid requirement with version specifier — let pip report the error
             else:
                 root = Path(from_file).parent
                 extras: list[str] = []

tests/tox_env/python/pip/req/test_file.py

@@ -550,6 +550,13 @@ def test_requirement_via_file_protocol_na(tmp_path: Path) -> None:
         assert req_file.options
 
 
+@pytest.mark.parametrize("req", ["pre-commit ~= 4", "pre-commit~=4"])
+def test_requirement_with_tilde_equals_not_treated_as_path(tmp_path: Path, req: str) -> None:
+    """Deps with ``~=`` version specifier should not be treated as local paths (#3447)."""
+    parsed = ParsedRequirement(req, {}, str(tmp_path / "tox.ini"), 1)
+    assert str(parsed.requirement) == req
+
+
 def test_requirement_to_path_one_level_up(tmp_path: Path) -> None:
     other_req = tmp_path / "other.txt"
     other_req.write_text("-e ..")