Move InstallRequirement.from_line to constructors module

src/pip/_internal/cli/base_command.py

@@ -22,9 +22,10 @@
 )
 from pip._internal.index import PackageFinder
 from pip._internal.locations import running_under_virtualenv
-from pip._internal.req.constructors import install_req_from_editable
+from pip._internal.req.constructors import (
+    install_req_from_editable, install_req_from_line,
+)
 from pip._internal.req.req_file import parse_requirements
-from pip._internal.req.req_install import InstallRequirement
 from pip._internal.utils.logging import setup_logging
 from pip._internal.utils.misc import get_prog, normalize_path
 from pip._internal.utils.outdated import pip_version_check
@@ -209,7 +210,7 @@ def populate_requirement_set(requirement_set, args, options, finder,
                 requirement_set.add_requirement(req_to_add)
 
         for req in args:
-            req_to_add = InstallRequirement.from_line(
+            req_to_add = install_req_from_line(
                 req, None, isolated=options.isolated_mode,
                 wheel_cache=wheel_cache
             )

src/pip/_internal/commands/uninstall.py

@@ -4,7 +4,8 @@
 
 from pip._internal.cli.base_command import Command
 from pip._internal.exceptions import InstallationError
-from pip._internal.req import InstallRequirement, parse_requirements
+from pip._internal.req import parse_requirements
+from pip._internal.req.constructors import install_req_from_line
 from pip._internal.utils.misc import protect_pip_from_modification_on_windows
 
 
@@ -47,7 +48,7 @@ def run(self, options, args):
         with self._build_session(options) as session:
             reqs_to_uninstall = {}
             for name in args:
-                req = InstallRequirement.from_line(
+                req = install_req_from_line(
                     name, isolated=options.isolated_mode,
                 )
                 if req.name:

src/pip/_internal/operations/freeze.py

@@ -10,8 +10,9 @@
 from pip._vendor.pkg_resources import RequirementParseError
 
 from pip._internal.exceptions import InstallationError
-from pip._internal.req import InstallRequirement
-from pip._internal.req.constructors import install_req_from_editable
+from pip._internal.req.constructors import (
+    install_req_from_editable, install_req_from_line,
+)
 from pip._internal.req.req_file import COMMENT_RE
 from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.misc import (
@@ -106,7 +107,7 @@ def freeze(
                             wheel_cache=wheel_cache,
                         )
                     else:
-                        line_req = InstallRequirement.from_line(
+                        line_req = install_req_from_line(
                             COMMENT_RE.sub('', line).strip(),
                             isolated=isolated,
                             wheel_cache=wheel_cache,

src/pip/_internal/req/constructors.py

@@ -8,18 +8,45 @@
 InstallRequirement.
 """
 
+import logging
 import os
+import re
+import traceback
 
+from pip._vendor.packaging.markers import Marker
 from pip._vendor.packaging.requirements import InvalidRequirement, Requirement
+from pip._vendor.packaging.specifiers import Specifier
+from pip._vendor.pkg_resources import RequirementParseError, parse_requirements
 
-# XXX: Temporarily importing _strip_extras
-from pip._internal.download import path_to_url, url_to_path
+from pip._internal.download import (
+    is_archive_file, is_url, path_to_url, url_to_path,
+)
 from pip._internal.exceptions import InstallationError
 from pip._internal.models.link import Link
-from pip._internal.req.req_install import InstallRequirement, _strip_extras
+from pip._internal.req.req_install import InstallRequirement
+from pip._internal.utils.misc import is_installable_dir
 from pip._internal.vcs import vcs
+from pip._internal.wheel import Wheel
 
-__all__ = ["install_req_from_editable", "parse_editable"]
+__all__ = [
+    "install_req_from_editable", "install_req_from_line",
+    "parse_editable"
+]
+
+logger = logging.getLogger(__name__)
+operators = Specifier._operators.keys()
+
+
+def _strip_extras(path):
+    m = re.match(r'^(.+)(\[[^\]]+\])$', path)
+    extras = None
+    if m:
+        path_no_extras = m.group(1)
+        extras = m.group(2)
+    else:
+        path_no_extras = path
+
+    return path_no_extras, extras
 
 
 def parse_editable(editable_req):
@@ -87,6 +114,36 @@ def parse_editable(editable_req):
     return package_name, url, None
 
 
+def deduce_helpful_msg(req):
+    """Returns helpful msg in case requirements file does not exist,
+    or cannot be parsed.
+
+    :params req: Requirements file path
+    """
+    msg = ""
+    if os.path.exists(req):
+        msg = " It does exist."
+        # Try to parse and check if it is a requirements file.
+        try:
+            with open(req, 'r') as fp:
+                # parse first line only
+                next(parse_requirements(fp.read()))
+                msg += " The argument you provided " + \
+                    "(%s) appears to be a" % (req) + \
+                    " requirements file. If that is the" + \
+                    " case, use the '-r' flag to install" + \
+                    " the packages specified within it."
+        except RequirementParseError:
+            logger.debug("Cannot parse '%s' as requirements \
+            file" % (req), exc_info=1)
+    else:
+        msg += " File '%s' does not exist." % (req)
+    return msg
+
+
+# ---- The actual constructors follow ----
+
+
 def install_req_from_editable(
     editable_req, comes_from=None, isolated=False, options=None,
     wheel_cache=None, constraint=False
@@ -114,3 +171,102 @@ def install_req_from_editable(
         wheel_cache=wheel_cache,
         extras=extras_override or (),
     )
+
+
+def install_req_from_line(
+    name, comes_from=None, isolated=False, options=None, wheel_cache=None,
+    constraint=False
+):
+    """Creates an InstallRequirement from a name, which might be a
+    requirement, directory containing 'setup.py', filename, or URL.
+    """
+    if is_url(name):
+        marker_sep = '; '
+    else:
+        marker_sep = ';'
+    if marker_sep in name:
+        name, markers = name.split(marker_sep, 1)
+        markers = markers.strip()
+        if not markers:
+            markers = None
+        else:
+            markers = Marker(markers)
+    else:
+        markers = None
+    name = name.strip()
+    req = None
+    path = os.path.normpath(os.path.abspath(name))
+    link = None
+    extras = None
+
+    if is_url(name):
+        link = Link(name)
+    else:
+        p, extras = _strip_extras(path)
+        looks_like_dir = os.path.isdir(p) and (
+            os.path.sep in name or
+            (os.path.altsep is not None and os.path.altsep in name) or
+            name.startswith('.')
+        )
+        if looks_like_dir:
+            if not is_installable_dir(p):
+                raise InstallationError(
+                    "Directory %r is not installable. Neither 'setup.py' "
+                    "nor 'pyproject.toml' found." % name
+                )
+            link = Link(path_to_url(p))
+        elif is_archive_file(p):
+            if not os.path.isfile(p):
+                logger.warning(
+                    'Requirement %r looks like a filename, but the '
+                    'file does not exist',
+                    name
+                )
+            link = Link(path_to_url(p))
+
+    # it's a local file, dir, or url
+    if link:
+        # Handle relative file URLs
+        if link.scheme == 'file' and re.search(r'\.\./', link.url):
+            link = Link(
+                path_to_url(os.path.normpath(os.path.abspath(link.path))))
+        # wheel file
+        if link.is_wheel:
+            wheel = Wheel(link.filename)  # can raise InvalidWheelFilename
+            req = "%s==%s" % (wheel.name, wheel.version)
+        else:
+            # set the req to the egg fragment.  when it's not there, this
+            # will become an 'unnamed' requirement
+            req = link.egg_fragment
+
+    # a requirement specifier
+    else:
+        req = name
+
+    if extras:
+        extras = Requirement("placeholder" + extras.lower()).extras
+    else:
+        extras = ()
+    if req is not None:
+        try:
+            req = Requirement(req)
+        except InvalidRequirement:
+            if os.path.sep in req:
+                add_msg = "It looks like a path."
+                add_msg += deduce_helpful_msg(req)
+            elif '=' in req and not any(op in req for op in operators):
+                add_msg = "= is not a valid operator. Did you mean == ?"
+            else:
+                add_msg = traceback.format_exc()
+            raise InstallationError(
+                "Invalid requirement: '%s'\n%s" % (req, add_msg)
+            )
+
+    return InstallRequirement(
+        req, comes_from, link=link, markers=markers,
+        isolated=isolated,
+        options=options if options else {},
+        wheel_cache=wheel_cache,
+        constraint=constraint,
+        extras=extras,
+    )

src/pip/_internal/req/req_file.py

@@ -16,8 +16,9 @@
 from pip._internal.cli import cmdoptions
 from pip._internal.download import get_file_content
 from pip._internal.exceptions import RequirementsFileParseError
-from pip._internal.req.constructors import install_req_from_editable
-from pip._internal.req.req_install import InstallRequirement
+from pip._internal.req.constructors import (
+    install_req_from_editable, install_req_from_line,
+)
 
 __all__ = ['parse_requirements']
 
@@ -152,7 +153,7 @@ def process_line(line, filename, line_number, finder=None, comes_from=None,
         for dest in SUPPORTED_OPTIONS_REQ_DEST:
             if dest in opts.__dict__ and opts.__dict__[dest]:
                 req_options[dest] = opts.__dict__[dest]
-        yield InstallRequirement.from_line(
+        yield install_req_from_line(
             args_str, line_comes_from, constraint=constraint,
             isolated=isolated, options=req_options, wheel_cache=wheel_cache
         )