[interactive] Initial implementation of PROMPT_COMMAND (#414)

- Location information is wrong - PROMPT_COMMAND=';' gives a traceback pointing to ~/.local/oil/oshrc instead of [ interactive ] or [ PROMPT_COMMAND ]
- Don't let command change status

Addresses #400

core/main_loop.py

@@ -18,9 +18,9 @@
     command_t, command,
     parse_result__EmptyLine, parse_result__Eof, parse_result__Node
 )
+from _devbuild.gen.runtime_asdl import value_e, arg_vector
 from core import ui
 from core import util
-#from core.util import log
 
 from typing import Any, Optional, List, TYPE_CHECKING
 if TYPE_CHECKING:
@@ -31,6 +31,23 @@
   #from osh.cmd_exec import Executor
 
 
+def _ExecutePromptCommand(ex):
+  # type: (Any) -> None
+  prompt_var = ex.mem.GetVar('PROMPT_COMMAND')
+  # Undefined, Array, or AssociativeArray
+  if prompt_var.tag != value_e.Str:
+    return
+  command = prompt_var.s
+
+  # save this so PROMPT_COMMAND can't set $?
+  ex.mem.PushStatusFrame()
+  arg_vec = arg_vector(['PROMPT_COMMAND', command], [0, 0])
+  try:
+    ex._Eval(arg_vec)
+  finally:
+    ex.mem.PopStatusFrame()
+
+
 def Interactive(opts, ex, c_parser, display, errfmt):
   # type: (Any, Any, CommandParser, Any, ErrorFormatter) -> Any
   status = 0
@@ -42,6 +59,7 @@ def Interactive(opts, ex, c_parser, display, errfmt):
     # it appears in all branches.
 
     while True:  # ONLY EXECUTES ONCE
+      _ExecutePromptCommand(ex)
       try:
         # may raise HistoryError or ParseError
         result = c_parser.ParseInteractiveLine()

spec/interactive.test.sh

@@ -20,7 +20,11 @@ one
 #### fatal errors continue
 
 # NOTE: tried here doc, but sys.stdin.isatty() fails.  Could we fake it?
-$SH -i -c '
+case "$SH" in
+	*bash) FLAGS='--noprofile --norc';;
+	*osh) FLAGS='--rcfile /dev/null';;
+esac
+$SH $FLAGS -i -c '
 echo $(( 1 / 0 ))
 echo one
 exit 42
@@ -51,3 +55,13 @@ RCFILE
 ## N-I dash status: 2
 ## N-I mksh status: 1
 
+#### interactive shell runs PROMPT_COMMAND after each command
+TEST_CASE='PROMPT_COMMAND="echo hi"'
+case $SH in
+	*bash) echo "$TEST_CASE" | $SH --noprofile --norc -i;;
+	*osh) $SH --rcfile /dev/null -i -c "$TEST_CASE";;
+	*) $SH -i -c "$TEST_CASE";;
+esac
+## STDOUT:
+hi
+## N-I dash/mksh stdout-json: ""