Fix zsh completion script (#12173)

Author: pradyunsg

news/12166.bugfix.rst

@@ -0,0 +1 @@
+Fix completion script for zsh

src/pip/_internal/commands/completion.py

@@ -23,9 +23,18 @@
     """,
     "zsh": """
         #compdef -P pip[0-9.]#
-        compadd $( COMP_WORDS="$words[*]" \\
-                   COMP_CWORD=$((CURRENT-1)) \\
-                   PIP_AUTO_COMPLETE=1 $words[1] 2>/dev/null )
+        __pip() {{
+          compadd $( COMP_WORDS="$words[*]" \\
+                     COMP_CWORD=$((CURRENT-1)) \\
+                     PIP_AUTO_COMPLETE=1 $words[1] 2>/dev/null )
+        }}
+        if [[ $zsh_eval_context[-1] == loadautofunc ]]; then
+          # autoload from fpath, call function directly
+          __pip "$@"
+        else
+          # eval/source/. command, register function for later
+          compdef __pip -P 'pip[0-9.]#'
+        fi
     """,
     "fish": """
         function __fish_complete_pip

tests/functional/test_completion.py

@@ -44,9 +44,18 @@
         "zsh",
         """\
 #compdef -P pip[0-9.]#
-compadd $( COMP_WORDS="$words[*]" \\
-           COMP_CWORD=$((CURRENT-1)) \\
-           PIP_AUTO_COMPLETE=1 $words[1] 2>/dev/null )""",
+__pip() {
+  compadd $( COMP_WORDS="$words[*]" \\
+             COMP_CWORD=$((CURRENT-1)) \\
+             PIP_AUTO_COMPLETE=1 $words[1] 2>/dev/null )
+}
+if [[ $zsh_eval_context[-1] == loadautofunc ]]; then
+  # autoload from fpath, call function directly
+  __pip "$@"
+else
+  # eval/source/. command, register function for later
+  compdef __pip -P 'pip[0-9.]#'
+fi""",
     ),
     (
         "powershell",