import configparser
import logging
import os
from typing import List, Optional, Tuple

from pip._internal.exceptions import BadCommand, InstallationError
from pip._internal.utils.misc import HiddenText, display_path
from pip._internal.utils.subprocess import make_command
from pip._internal.utils.urls import path_to_url
from pip._internal.vcs.versioncontrol import (
    RevOptions,
    VersionControl,
    find_path_to_project_root_from_repo_root,
    vcs,
)

logger = logging.getLogger(__name__)


class Mercurial(VersionControl):
    name = "hg"
    dirname = ".hg"
    repo_name = "clone"
    schemes = (
        "hg+file",
        "hg+http",
        "hg+https",
        "hg+ssh",
        "hg+static-http",
    )

    @staticmethod
    def get_base_rev_args(rev: str) -> List[str]:
        return [f"-r={rev}"]

    def fetch_new(
        self, dest: str, url: HiddenText, rev_options: RevOptions, verbosity: int
    ) -> None:
        rev_display = rev_options.to_display()
        logger.info(
            "Cloning hg %s%s to %s",
            url,
            rev_display,
            display_path(dest),
        )
        if verbosity <= 0:
            flags: Tuple[str, ...] = ("--quiet",)
        elif verbosity == 1:
            flags = ()
        elif verbosity == 2:
            flags = ("--verbose",)
        else:
            flags = ("--verbose", "--debug")
        self.run_command(make_command("clone", "--noupdate", *flags, url, dest))
        self.run_command(
            make_command("update", *flags, rev_options.to_args()),
            cwd=dest,
        )

    def switch(self, dest: str, url: HiddenText, rev_options: RevOptions) -> None:
        repo_config = os.path.join(dest, self.dirname, "hgrc")
        config = configparser.RawConfigParser()
        try:
            config.read(repo_config)
            config.set("paths", "default", url.secret)
            with open(repo_config, "w") as config_file:
                config.write(config_file)
        except (OSError, configparser.NoSectionError) as exc:
            logger.warning("Could not switch Mercurial repository to %s: %s", url, exc)
        else:
            cmd_args = make_command("update", "-q", rev_options.to_args())
            self.run_command(cmd_args, cwd=dest)

    def update(self, dest: str, url: HiddenText, rev_options: RevOptions) -> None:
        self.run_command(["pull", "-q"], cwd=dest)
        cmd_args = make_command("update", "-q", rev_options.to_args())
        self.run_command(cmd_args, cwd=dest)

    @classmethod
    def get_remote_url(cls, location: str) -> str:
        url = cls.run_command(
            ["showconfig", "paths.default"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        if cls._is_local_repository(url):
            url = path_to_url(url)
        return url.strip()

    @classmethod
    def get_revision(cls, location: str) -> str:
        """
        Return the repository-local changeset revision number, as an integer.
        """
        current_revision = cls.run_command(
            ["parents", "--template={rev}"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        return current_revision

    @classmethod
    def get_requirement_revision(cls, location: str) -> str:
        """
        Return the changeset identification hash, as a 40-character
        hexadecimal string
        """
        current_rev_hash = cls.run_command(
            ["parents", "--template={node}"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        return current_rev_hash

    @classmethod
    def is_commit_id_equal(cls, dest: str, name: Optional[str]) -> bool:
        """Always assume the versions don't match"""
        return False

    @classmethod
    def get_subdirectory(cls, location: str) -> Optional[str]:
        """
        Return the path to Python project root, relative to the repo root.
        Return None if the project root is in the repo root.
        """
        # find the repo root
        repo_root = cls.run_command(
            ["root"], show_stdout=False, stdout_only=True, cwd=location
        ).strip()
        if not os.path.isabs(repo_root):
            repo_root = os.path.abspath(os.path.join(location, repo_root))
        return find_path_to_project_root_from_repo_root(location, repo_root)

    @classmethod
    def get_repository_root(cls, location: str) -> Optional[str]:
        loc = super().get_repository_root(location)
        if loc:
            return loc
        try:
            r = cls.run_command(
                ["root"],
                cwd=location,
                show_stdout=False,
                stdout_only=True,
                on_returncode="raise",
                log_failed_cmd=False,
            )
        except BadCommand:
            logger.debug(
                "could not determine if %s is under hg control "
                "because hg is not available",
                location,
            )
            return None
        except InstallationError:
            return None
        return os.path.normpath(r.rstrip("\r\n"))


vcs.register(Mercurial)

src/pip/_internal/vcs/mercurial.py
import configparser
import logging
import os
from typing import List, Optional, Tuple

from pip._internal.exceptions import BadCommand, InstallationError
from pip._internal.utils.misc import HiddenText, display_path
from pip._internal.utils.subprocess import make_command
from pip._internal.utils.urls import path_to_url
from pip._internal.vcs.versioncontrol import (
    RevOptions,
    VersionControl,
    find_path_to_project_root_from_repo_root,
    vcs,
)

logger = logging.getLogger(__name__)


class Mercurial(VersionControl):
    name = "hg"
    dirname = ".hg"
    repo_name = "clone"
    schemes = (
        "hg+file",
        "hg+http",
        "hg+https",
        "hg+ssh",
        "hg+static-http",
    )

    @staticmethod
    def get_base_rev_args(rev: str) -> List[str]:
        return [f"--rev={rev}"]

    def fetch_new(
        self, dest: str, url: HiddenText, rev_options: RevOptions, verbosity: int
    ) -> None:
        rev_display = rev_options.to_display()
        logger.info(
            "Cloning hg %s%s to %s",
            url,
            rev_display,
            display_path(dest),
        )
        if verbosity <= 0:
            flags: Tuple[str, ...] = ("--quiet",)
        elif verbosity == 1:
            flags = ()
        elif verbosity == 2:
            flags = ("--verbose",)
        else:
            flags = ("--verbose", "--debug")
        self.run_command(make_command("clone", "--noupdate", *flags, url, dest))
        self.run_command(
            make_command("update", *flags, rev_options.to_args()),
            cwd=dest,
        )

    def switch(self, dest: str, url: HiddenText, rev_options: RevOptions) -> None:
        repo_config = os.path.join(dest, self.dirname, "hgrc")
        config = configparser.RawConfigParser()
        try:
            config.read(repo_config)
            config.set("paths", "default", url.secret)
            with open(repo_config, "w") as config_file:
                config.write(config_file)
        except (OSError, configparser.NoSectionError) as exc:
            logger.warning("Could not switch Mercurial repository to %s: %s", url, exc)
        else:
            cmd_args = make_command("update", "-q", rev_options.to_args())
            self.run_command(cmd_args, cwd=dest)

    def update(self, dest: str, url: HiddenText, rev_options: RevOptions) -> None:
        self.run_command(["pull", "-q"], cwd=dest)
        cmd_args = make_command("update", "-q", rev_options.to_args())
        self.run_command(cmd_args, cwd=dest)

    @classmethod
    def get_remote_url(cls, location: str) -> str:
        url = cls.run_command(
            ["showconfig", "paths.default"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        if cls._is_local_repository(url):
            url = path_to_url(url)
        return url.strip()

    @classmethod
    def get_revision(cls, location: str) -> str:
        """
        Return the repository-local changeset revision number, as an integer.
        """
        current_revision = cls.run_command(
            ["parents", "--template={rev}"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        return current_revision

    @classmethod
    def get_requirement_revision(cls, location: str) -> str:
        """
        Return the changeset identification hash, as a 40-character
        hexadecimal string
        """
        current_rev_hash = cls.run_command(
            ["parents", "--template={node}"],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        return current_rev_hash

    @classmethod
    def is_commit_id_equal(cls, dest: str, name: Optional[str]) -> bool:
        """Always assume the versions don't match"""
        return False

    @classmethod
    def get_subdirectory(cls, location: str) -> Optional[str]:
        """
        Return the path to Python project root, relative to the repo root.
        Return None if the project root is in the repo root.
        """
        # find the repo root
        repo_root = cls.run_command(
            ["root"], show_stdout=False, stdout_only=True, cwd=location
        ).strip()
        if not os.path.isabs(repo_root):
            repo_root = os.path.abspath(os.path.join(location, repo_root))
        return find_path_to_project_root_from_repo_root(location, repo_root)

    @classmethod
    def get_repository_root(cls, location: str) -> Optional[str]:
        loc = super().get_repository_root(location)
        if loc:
            return loc
        try:
            r = cls.run_command(
                ["root"],
                cwd=location,
                show_stdout=False,
                stdout_only=True,
                on_returncode="raise",
                log_failed_cmd=False,
            )
        except BadCommand:
            logger.debug(
                "could not determine if %s is under hg control "
                "because hg is not available",
                location,
            )
            return None
        except InstallationError:
            return None
        return os.path.normpath(r.rstrip("\r\n"))


vcs.register(Mercurial)

src/pip/_internal/vcs/mercurial.py
diff --git a/news/370392cf-52cd-402c-b402-06d2ff398f89.bugfix.rst b/news/370392cf-52cd-402c-b402-06d2ff398f89.bugfix.rst
new file mode 100644
index 00000000000..76a8e6b96db
--- /dev/null
+++ b/news/370392cf-52cd-402c-b402-06d2ff398f89.bugfix.rst
@@ -0,0 +1 @@
+Fix mercurial revision "parse error": use ``--rev={ref}`` instead of ``-r={ref}``
diff --git a/src/pip/_internal/vcs/mercurial.py b/src/pip/_internal/vcs/mercurial.py
index e440c122169..c183d41d09c 100644
--- a/src/pip/_internal/vcs/mercurial.py
+++ b/src/pip/_internal/vcs/mercurial.py
@@ -31,7 +31,7 @@ class Mercurial(VersionControl):
 
     @staticmethod
     def get_base_rev_args(rev: str) -> List[str]:
-        return [f"-r={rev}"]
+        return [f"--rev={rev}"]
 
     def fetch_new(
         self, dest: str, url: HiddenText, rev_options: RevOptions, verbosity: int
diff --git a/tests/unit/test_vcs.py b/tests/unit/test_vcs.py
index 4a3750f2d36..5291f129cf7 100644
--- a/tests/unit/test_vcs.py
+++ b/tests/unit/test_vcs.py
@@ -66,7 +66,7 @@ def test_rev_options_repr() -> None:
         # First check VCS-specific RevOptions behavior.
         (Bazaar, [], ["-r", "123"], {}),
         (Git, ["HEAD"], ["123"], {}),
-        (Mercurial, [], ["-r=123"], {}),
+        (Mercurial, [], ["--rev=123"], {}),
         (Subversion, [], ["-r", "123"], {}),
         # Test extra_args.  For this, test using a single VersionControl class.
         (

After uprade pip to version 23.3+  cant use hg+http with current branch
### Description

After uprade pip to version 23.3+ can`t isntall my package from repository with current branch
if i use older version or without branch works fine, olready use tag and hash instead of branch

### Expected behavior

pip will work correctly

### pip version

23.3

### Python version

3.9

### OS

Linux

### How to Reproduce

try to install from hg repository using branch or hash
for example 
pip install hg+http://mylink/hg/folder/mypackage@0.1.3

### Output

Collecting hg+http://mylink/hg/folder/mypackage@0.1.3
  Cloning hg  http://mylink/hg/folder/mypackage (to revision 0.1.3) to /tmp/pip-req-build-hmzsjinv
  Running command hg clone --noupdate --quiet http://mylink/hg/folder/mypackage /tmp/pip-req-build-hmzsjinv

  Running command hg update --quiet -r=0.1.3
  hg: parse error at 0: not a prefix: =
  (=0.1.3
   ^ here)
  error: subprocess-exited-with-error
  
  × hg update --quiet -r=0.1.3 did not run successfully.
  │ exit code: 255
  ╰─> See above for output.
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: subprocess-exited-with-error

× hg update --quiet -r=0.1.3 did not run successfully.
│ exit code: 255
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.

### Code of Conduct

- [X] I agree to follow the [PSF Code of Conduct](https://www.python.org/psf/conduct/).
