bpo-37663: have venv activation scripts all consistently use __VENV_PROMPT__ for prompt customization (GH-14941)

The activation scripts generated by venv were inconsistent in how they changed the shell's prompt. Some used `__VENV_PROMPT__` exclusively, some used `__VENV_PROMPT__` if it was set even though by default `__VENV_PROMPT__` is always set and the fallback matched the default, and one ignored `__VENV_PROMPT__` and used `__VENV_NAME__` instead (and even used a differing format to the default prompt). This change now has all activation scripts use `__VENV_PROMPT__` only and relies on the fact that venv sets that value by default.

The color of the customization is also now set in fish to the blue from the Python logo for as hex color support is built into that shell (much like PowerShell where the built-in green color is used).

5 files changed, 30 insertions, 46 deletions

diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index f09e09c..6615a2e 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -118,6 +118,16 @@ finalization crashed with a Python fatal error if a daemon thread was still
 running.
 (Contributed by Victor Stinner in :issue:`37266`.)
 
+venv
+----
+
+The activation scripts provided by :mod:`venv` now all specify their prompt
+customization consistently by always using the value specified by
+``__VENV_PROMPT__``. Previously some scripts unconditionally used
+``__VENV_PROMPT__``, others only if it happened to be set (which was the default
+case), and one used ``__VENV_NAME__`` instead.
+(Contributed by Brett Cannon in :issue:`37663`.)
+
 pprint
 ------
 
@@ -191,12 +201,14 @@ Removed
   Use :meth:`~threading.Thread.is_alive()` instead.
   (Contributed by Dong-hee Na in :issue:`37804`.)
 
+
 Porting to Python 3.9
 =====================
 
 This section lists previously described changes and other bugfixes
 that may require changes to your code.
 
+
 Changes in the Python API
 -------------------------
 
@@ -205,3 +217,6 @@ Changes in the Python API
   catching the specific exception type and supporting both Python 3.9 and
   earlier versions will need to catch both:
   ``except (ImportError, ValueError):``
+
+* The :mod:`venv` activation scripts no longer special-case when
+  ``__VENV_PROMPT__`` is set to ``""``.
diff --git a/Lib/venv/scripts/common/activate b/Lib/venv/scripts/common/activate
index fff0765..6a2320a 100644
--- a/Lib/venv/scripts/common/activate
+++ b/Lib/venv/scripts/common/activate
@@ -54,17 +54,7 @@ fi
 
 if [ -z "${VIRTUAL_ENV_DISABLE_PROMPT:-}" ] ; then
     _OLD_VIRTUAL_PS1="${PS1:-}"
-    if [ "x__VENV_PROMPT__" != x ] ; then
-	PS1="__VENV_PROMPT__${PS1:-}"
-    else
-    if [ "`basename \"$VIRTUAL_ENV\"`" = "__" ] ; then
-        # special case for Aspen magic directories
-        # see http://www.zetadev.com/software/aspen/
-        PS1="[`basename \`dirname \"$VIRTUAL_ENV\"\``] $PS1"
-    else
-        PS1="(`basename \"$VIRTUAL_ENV\"`)$PS1"
-    fi
-    fi
+    PS1="__VENV_PROMPT__${PS1:-}"
     export PS1
 fi
 
diff --git a/Lib/venv/scripts/posix/activate.csh b/Lib/venv/scripts/posix/activate.csh
index b0c7028..68a0dc7 100644
--- a/Lib/venv/scripts/posix/activate.csh
+++ b/Lib/venv/scripts/posix/activate.csh
@@ -17,19 +17,7 @@ setenv PATH "$VIRTUAL_ENV/__VENV_BIN_NAME__:$PATH"
 set _OLD_VIRTUAL_PROMPT="$prompt"
 
 if (! "$?VIRTUAL_ENV_DISABLE_PROMPT") then
-    if ("__VENV_NAME__" != "") then
-        set env_name = "__VENV_NAME__"
-    else
-        if (`basename "VIRTUAL_ENV"` == "__") then
-            # special case for Aspen magic directories
-            # see http://www.zetadev.com/software/aspen/
-            set env_name = `basename \`dirname "$VIRTUAL_ENV"\``
-        else
-            set env_name = `basename "$VIRTUAL_ENV"`
-        endif
-    endif
-    set prompt = "[$env_name] $prompt"
-    unset env_name
+    set prompt = "__VENV_PROMPT__$prompt"
 endif
 
 alias pydoc python -m pydoc
diff --git a/Lib/venv/scripts/posix/activate.fish b/Lib/venv/scripts/posix/activate.fish
index b401058..777d51c 100644
--- a/Lib/venv/scripts/posix/activate.fish
+++ b/Lib/venv/scripts/posix/activate.fish
@@ -1,5 +1,5 @@
-# This file must be used with ". bin/activate.fish" *from fish* (http://fishshell.org)
-# you cannot run it directly
+# This file must be used with ". bin/activate.fish" *from fish* (http://fishshell.org);
+# you cannot run it directly.
 
 function deactivate  -d "Exit virtualenv and return to normal shell environment"
     # reset old environment variables
@@ -21,12 +21,12 @@ function deactivate  -d "Exit virtualenv and return to normal shell environment"
 
     set -e VIRTUAL_ENV
     if test "$argv[1]" != "nondestructive"
-        # Self destruct!
+        # Self-destruct!
         functions -e deactivate
     end
 end
 
-# unset irrelevant variables
+# Unset irrelevant variables.
 deactivate nondestructive
 
 set -gx VIRTUAL_ENV "__VENV_DIR__"
@@ -34,7 +34,7 @@ set -gx VIRTUAL_ENV "__VENV_DIR__"
 set -gx _OLD_VIRTUAL_PATH $PATH
 set -gx PATH "$VIRTUAL_ENV/__VENV_BIN_NAME__" $PATH
 
-# unset PYTHONHOME if set
+# Unset PYTHONHOME if set.
 if set -q PYTHONHOME
     set -gx _OLD_VIRTUAL_PYTHONHOME $PYTHONHOME
     set -e PYTHONHOME
@@ -43,31 +43,20 @@ end
 if test -z "$VIRTUAL_ENV_DISABLE_PROMPT"
     # fish uses a function instead of an env var to generate the prompt.
 
-    # save the current fish_prompt function as the function _old_fish_prompt
+    # Save the current fish_prompt function as the function _old_fish_prompt.
     functions -c fish_prompt _old_fish_prompt
 
-    # with the original prompt function renamed, we can override with our own.
+    # With the original prompt function renamed, we can override with our own.
     function fish_prompt
-        # Save the return status of the last command
+        # Save the return status of the last command.
         set -l old_status $status
 
-        # Prompt override?
-        if test -n "__VENV_PROMPT__"
-            printf "%s%s" "__VENV_PROMPT__" (set_color normal)
-        else
-            # ...Otherwise, prepend env
-            set -l _checkbase (basename "$VIRTUAL_ENV")
-            if test $_checkbase = "__"
-                # special case for Aspen magic directories
-                # see http://www.zetadev.com/software/aspen/
-                printf "%s[%s]%s " (set_color -b blue white) (basename (dirname "$VIRTUAL_ENV")) (set_color normal)
-            else
-                printf "%s(%s)%s" (set_color -b blue white) (basename "$VIRTUAL_ENV") (set_color normal)
-            end
-        end
+        # Output the venv prompt; color taken from the blue of the Python logo.
+        printf "%s%s%s" (set_color 4B8BBE) "__VENV_PROMPT__" (set_color normal)
 
         # Restore the return status of the previous command.
         echo "exit $old_status" | .
+        # Output the original/"old" prompt.
         _old_fish_prompt
     end
 
diff --git a/Misc/NEWS.d/next/Library/2019-07-24-14-38-53.bpo-37663.h4-9-1.rst b/Misc/NEWS.d/next/Library/2019-07-24-14-38-53.bpo-37663.h4-9-1.rst
new file mode 100644
index 0000000..1f9f9d9
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-07-24-14-38-53.bpo-37663.h4-9-1.rst
@@ -0,0 +1,2 @@
+Bring consistency to venv shell activation scripts by always using
+__VENV_PROMPT__.