Add pip completion documentation

docs/html/cli/index.md

@@ -30,6 +30,13 @@ pip_check
 pip_lock
 ```
 
+```{toctree}
+:maxdepth: 1
+:caption: Command-line usability and shell integration
+
+pip_completion
+```
+
 ```{toctree}
 :maxdepth: 1
 :caption: Handling Distribution Files

docs/html/cli/pip_completion.rst

@@ -0,0 +1,72 @@
+.. _`pip completion`:
+
+==============
+pip completion
+==============
+
+
+Usage
+=====
+
+.. tab:: Unix/macOS
+
+   .. pip-command-usage:: completion "python -m pip"
+
+.. tab:: Windows
+
+   .. pip-command-usage:: completion "py -m pip"
+
+
+Description
+===========
+
+.. pip-command-description:: completion
+
+Options
+=======
+
+.. pip-command-options:: completion
+
+Examples
+========
+
+Enable bash completion:
+
+.. code-block:: console
+
+    $ python -m pip completion --bash
+    # pip bash completion start
+    _pip_completion()
+    {
+        COMPREPLY=( $( COMP_WORDS="${COMP_WORDS[*]}" \
+                    COMP_CWORD=$COMP_CWORD \
+                    PIP_AUTO_COMPLETE=1 $1 2>/dev/null ) )
+    }
+    complete -o default -F _pip_completion /usr/bin/python -m pip
+    # pip bash completion end
+
+Enable PowerShell completion:
+
+.. code-block:: console
+
+    > py -m pip completion --powershell
+    if ((Test-Path Function:\\TabExpansion) -and -not `
+    (Test-Path Function:\\_pip_completeBackup)) {{
+    Rename-Item Function:\\TabExpansion _pip_completeBackup
+    }}
+    function TabExpansion($line, $lastWord) {{
+        $lastBlock = [regex]::Split($line, '[|;]')[-1].TrimStart()
+        if ($lastBlock.StartsWith("{prog} ")) {{
+            $Env:COMP_WORDS=$lastBlock
+            $Env:COMP_CWORD=$lastBlock.Split().Length - 1
+            $Env:PIP_AUTO_COMPLETE=1
+            (& {prog}).Split()
+            Remove-Item Env:COMP_WORDS
+            Remove-Item Env:COMP_CWORD
+            Remove-Item Env:PIP_AUTO_COMPLETE
+        }}
+        elseif (Test-Path Function:\\_pip_completeBackup) {{
+            # Fall back on existing tab expansion
+            _pip_completeBackup $line $lastWord
+        }}
+    }}

news/13536.doc.rst

@@ -0,0 +1 @@
+Add ``pip completion`` documentation.

src/pip/_internal/commands/completion.py

@@ -81,6 +81,8 @@ class CompletionCommand(Command):
     """A helper command to be used for command completion."""
 
     ignore_require_venv = True
+    usage = """
+      %prog [options]"""
 
     def add_options(self) -> None:
         self.cmd_opts.add_option(