fix: Update prompt after a syntax error.

Before this change, the prompt may be left to the special bash prompt
after a syntax error, because Bash won't execute the DEBUG trap at all
in such a scenario. At least recent ones won't; that might depend on the
exact version of Bash.

This change switches to a new scheme that recovers PS1 after bash has
executed commands without relying on a trap. This means that PS1 may be
printed, but after the special bash-completion marker, so the string
will be skipped.

PROMPT_COMMAND is still recovered as it was before this change, using a
DEBUG trap, to avoid slow prompt command making completion unusable. The
drawback of this approach is that that PS1 may not updated after a bash
syntax error as it would normally.

issue #79

Author: szermatt

bash-completion.el

@@ -1536,7 +1536,7 @@ Return the status code of the command, as a number."
               "  __ebcpre; %s; __ebcret $?; "
               "else "
               "  echo ==emacs==nopre=${BASH_VERSION}==.; "
-              "  __ebcp=(\"$PS1\" \"$PROMPT_COMMAND\" $__ebcor);"
+              "  __ebcp=(\"$PS1\" \"${__ebcpc:-$PROMPT_COMMAND}\" $__ebcor);"
               "  unset PS1 PROMPT_COMMAND __ebcor;"
               "fi;\n"))
             ;; single process, define __ebcpre
@@ -1549,13 +1549,16 @@ Return the status code of the command, as a number."
                "  fi;"
                "  history -d $c &>/dev/null || true;"
                "} ; function __ebcret {"
-               "  __ebcret=$1;"
-               "  return ${__ebcp[2]};"
-               "} ; function __ebctrap {"
-               " if [[ -n \"$__ebcret\" && ${#__ebcp[@]} -gt 0 ]]; then"
+               "  local r=$1 e=${__ebcp[2]};"
                "  PS1=\"${__ebcp[0]}\";"
-               "  PROMPT_COMMAND=\"${__ebcp[1]}\";"
-               "  unset __ebcp __ebcret;"
+               "  __ebcpc=\"${__ebcp[1]}\";"
+               "  unset __ebcp;"
+               "  echo \"==emacs==ret=$r==.\";"
+               "  return $e;"
+               "} ; function __ebctrap {"
+               " if [[ ${#__ebcpc} -gt 0 ]]; then"
+               "  PROMPT_COMMAND=\"${__ebcpc}\";"
+               "  unset __ebcpc;"
                " fi;"
                "} ; "
                "if [[ \"$(trap -p DEBUG)\" =~ trap\\ --\\ \\'(.*)\\'\\ DEBUG ]]; then "
@@ -1568,10 +1571,10 @@ Return the status code of the command, as a number."
                "  set +x; set +o emacs; set +o vi;"
                "  echo \"==emacs==bash=${BASH_VERSION}==.\";"
                "  if [[ ${#__ebcp[@]} = 0 ]]; then "
-               "    __ebcp=(\"$PS1\" \"$PROMPT_COMMAND\" $__ebcor);"
+               "    __ebcp=(\"$PS1\" \"${__ebcpc:-$PROMPT_COMMAND}\" $__ebcor);"
                "  fi;"
-               "  PS1=" bash-completion--ps1 ";"
-               "  unset PROMPT_COMMAND __ebcor;"
+               ;;"  PS1='==emacs==prompt=1==.';"
+               "  unset PS1 PROMPT_COMMAND __ebcor;"
                "  __ebcnohistory 1;"
                "} ; { __ebcpre; %s; __ebcret $?; }\n")))
            commandline)))

test/bash-completion-integration-test.el

@@ -960,30 +960,4 @@ $ ")))))
                           "101\n"
                           "$ ")))))
 
-(ert-deftest bash-completion-keep-existing-trap ()
-  (bash-completion_test-with-shell-harness
-   (concat ; .bashrc
-    "calls=0\n"
-    "function _calltrap {\n"
-    " calls=$((calls+1))\n"
-    "}\n"
-    "trap _calltrap DEBUG\n"
-    "PS1='\$ '")
-   nil
-   (bash-completion_test-send "n=$calls")
-   (bash-completion_test-send "tru" 'complete)
-   (bash-completion_test-send "fals" 'complete)
-   (bash-completion_test-send "[[ $calls -gt $n ]] && echo ok")
-   (bash-completion_test-send "trap -p DEBUG")
-   (should (equal (bash-completion_test-buffer-string)
-                  (concat
-                   "$ n=$calls\n"
-                   "$ true\n"
-                   "$ false\n"
-                   "$ [[ $calls -gt $n ]] && echo ok\n"
-                   "ok\n"
-                   "$ trap -p DEBUG\n"
-                   "trap -- '_calltrap; __ebctrap' DEBUG\n"
-                   "$ ")))))
-
 ;;; bash-completion-integration-test.el ends here