add: allow specification of PEP 508 dependencies

With this change, users can now add dependencies using valid PEP 508
strings.

src/poetry/utils/dependency_specification.py

 from __future__ import annotations
 
+import contextlib
 import os
 import re
 import urllib.parse
@@ -9,6 +10,10 @@ from typing import TYPE_CHECKING
 from typing import Dict
 from typing import List
 from typing import Union
+from typing import cast
+
+from poetry.core.packages.dependency import Dependency
+from poetry.core.packages.vcs_dependency import VCSDependency
 
 from poetry.puzzle.provider import Provider
 
@@ -53,7 +58,7 @@ def _parse_dependency_specification_url(
 
     if url_parsed.scheme in ["http", "https"]:
         package = Provider.get_package_from_url(requirement)
-        return {"name": package.name, "url": package.source_url}
+        return {"name": package.name, "url": cast(str, package.source_url)}
 
     return None
 
@@ -131,12 +136,57 @@ def _parse_dependency_specification_simple(
     return require
 
 
+def dependency_to_specification(dependency: Dependency) -> DependencySpec:
+    specification: DependencySpec = {}
+
+    if dependency.is_vcs():
+        dependency = cast(VCSDependency, dependency)
+        specification[dependency.vcs] = cast(str, dependency.source_url)
+        if dependency.reference:
+            specification["rev"] = dependency.reference
+    elif dependency.is_file() or dependency.is_directory():
+        specification["path"] = cast(str, dependency.source_url)
+    elif dependency.is_url():
+        specification["url"] = cast(str, dependency.source_url)
+    elif dependency.pretty_constraint != "*" and not dependency.constraint.is_empty():
+        specification["version"] = dependency.pretty_constraint
+
+    if not dependency.marker.is_any():
+        specification["markers"] = str(dependency.marker)
+
+    if dependency.extras:
+        specification["extras"] = sorted(dependency.extras)
+
+    return specification
+
+
+def pep508_to_dependency_specification(requirement: str) -> DependencySpec | None:
+    if " ; " not in requirement and re.search(r"@[\^~!=<>\d]", requirement):
+        # this is of the form package@<semver>, do not attempt to parse it
+        return None
+
+    with contextlib.suppress(ValueError):
+        dependency = Dependency.create_from_pep_508(requirement)
+        specification = dependency_to_specification(dependency)
+
+        if specification:
+            specification["name"] = dependency.name
+            return specification
+
+    return None
+
+
 def parse_dependency_specification(
     requirement: str, env: Env | None = None, cwd: Path | None = None
 ) -> DependencySpec:
     requirement = requirement.strip()
     cwd = cwd or Path.cwd()
 
+    specification = pep508_to_dependency_specification(requirement)
+
+    if specification is not None:
+        return specification
+
     extras = []
     extras_m = re.search(r"\[([\w\d,-_ ]+)\]$", requirement)
     if extras_m:

tests/utils/test_dependency_specification.py

@@ -38,6 +38,9 @@ if TYPE_CHECKING:
         ("demo", {"name": "demo"}),
         ("demo@1.0.0", {"name": "demo", "version": "1.0.0"}),
         ("demo@^1.0.0", {"name": "demo", "version": "^1.0.0"}),
+        ("demo@==1.0.0", {"name": "demo", "version": "==1.0.0"}),
+        ("demo@!=1.0.0", {"name": "demo", "version": "!=1.0.0"}),
+        ("demo@~1.0.0", {"name": "demo", "version": "~1.0.0"}),
         ("demo[a,b]@1.0.0", {"name": "demo", "version": "1.0.0", "extras": ["a", "b"]}),
         ("demo[a,b]", {"name": "demo", "extras": ["a", "b"]}),
         ("../demo", {"name": "demo", "path": "../demo"}),
@@ -46,6 +49,47 @@ if TYPE_CHECKING:
             "https://example.com/packages/demo-0.1.0.tar.gz",
             {"name": "demo", "url": "https://example.com/packages/demo-0.1.0.tar.gz"},
         ),
+        # PEP 508 inputs
+        (
+            "poetry-core (>=1.0.7,<1.1.0)",
+            {"name": "poetry-core", "version": ">=1.0.7,<1.1.0"},
+        ),
+        (
+            'requests [security,tests] >= 2.8.1, == 2.8.* ; python_version < "2.7"',
+            {
+                "name": "requests",
+                "markers": 'python_version < "2.7"',
+                "version": ">=2.8.1,<2.9.0",
+                "extras": ["security", "tests"],
+            },
+        ),
+        ("name (>=3,<4)", {"name": "name", "version": ">=3,<4"}),
+        (
+            "name@http://foo.com",
+            {"name": "name", "url": "http://foo.com"},
+        ),
+        (
+            "name [fred,bar] @ http://foo.com ; python_version=='2.7'",
+            {
+                "name": "name",
+                "markers": 'python_version == "2.7"',
+                "url": "http://foo.com",
+                # This is commented out as there is a bug in
+                # Dependency.create_from_pep_508 that leads to incorrect
+                # URL Dependency creation.
+                # should be: "extras": ["fred", "bar"],
+            },
+        ),
+        (
+            'cachecontrol[filecache] (>=0.12.9,<0.13.0); python_version >= "3.6" and'
+            ' python_version < "4.0"',
+            {
+                "version": ">=0.12.9,<0.13.0",
+                "markers": 'python_version >= "3.6" and python_version < "4.0"',
+                "extras": ["filecache"],
+                "name": "cachecontrol",
+            },
+        ),
     ],
 )
 def test_parse_dependency_specification(
@@ -60,4 +104,6 @@ def test_parse_dependency_specification(
 
     mocker.patch("pathlib.Path.exists", _mock)
 
-    assert not DeepDiff(parse_dependency_specification(requirement), specification)
+    assert not DeepDiff(
+        parse_dependency_specification(requirement), specification, ignore_order=True
+    )