Scope the libedit hack to PEX scies.

CHANGES.md

@@ -2,11 +2,12 @@
 
 ## 2.16.1
 
-This release fixes the PEX repl for Pythons that use some versions of
-libedit to support readline functionality. For those versions, ansi
-terminal escape sequences for prompt colorization were not working.
+This release fixes the PEX repl for [Python Standalone Builds][PBS]
+CPython PEX scies. These PEXes ship using a version of libedit for
+readline support that does not support naive use of ansi terminal
+escape sequences for prompt colorization.
 
-* Fix PEX repl prompt for libedit. (#2503)
+* Fix PEX repl prompt for PBS libedit. (#2503)
 
 ## 2.16.0
 

pex/repl/custom.py

@@ -85,6 +85,7 @@ def repl_loop(
     custom_commands=None,  # type: Optional[Mapping[str, Tuple[Callable, str]]]
     history=False,  # type: bool
     history_file=None,  # type: Optional[str]
+    use_libedit_color_prompt_workaround=False,  # type: bool
 ):
     # type: (...) -> Callable[[], Dict[str, Any]]
 
@@ -123,7 +124,7 @@ def fixup_ansi(
 
         if not sys.stdout.isatty():
             text = _ANSI_RE.sub("", text)
-        elif prompt and libedit:
+        elif prompt and libedit and use_libedit_color_prompt_workaround:
             # Most versions of libedit do not support ansi terminal escape sequences, but they do
             # support a readline back door where you can bracket characters that should be ignored
             # for prompt width calculation but otherwise passed through unaltered to the terminal.

pex/repl/pex_repl.py

@@ -130,6 +130,9 @@ def pex(json=False):
         },
         history=history,
         history_file=history_file,
+        # The PBS CPythons used by PEX scies use a version of libedit that needs workarounds to
+        # support color prompts.
+        use_libedit_color_prompt_workaround=os.environ.get("SCIE") is not None,
     )