bug#33016: 26.1; (make-process ...) doesn't signal an error, when executable given as absolute Windows path does not exist

[Noam Postavsky <npostavs@gmail.com>]

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On Thu, 11 Oct 2018 at 08:57, Klaus-Dieter Bauer
<bauer.klaus.dieter@gmail.com> wrote:

>     M-x eval-expression RET
>       (make-process :name "test" :command '("c:/No Such Command"))
>
> will merely display in the echo-area message:
>
>     eval: Spawning child process: Invalid argument

The confusing thing here is that the error is signaled between
block_input()...unblock_input(), which prevents the debugger from
triggering. E.g., the "-unless-debug" part in the expression below
appears not to work, even though the error flows normally in other
respects:

(condition-case-unless-debug err
    (make-process :name "test" :command '("c:/No Such Command"))
  (error (list :error err)))
;=> (:error (file-error "Spawning child process" "Invalid argument"))

The attached patch fixes this by moving the signal to after the unblock_input().

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From d8716c1406301512fbbfce7f1eeb45fc8d531fd1 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Mon, 8 Apr 2019 13:16:38 -0400
Subject: [PATCH v1] Let debugger handle process spawn errors on w32
 (Bug#33016)

When an error is signaled between block_input()...unblock_input(), the
Lisp debugger is prevented from starting.
* src/callproc.c (child_setup): Move the report_file_error call from here...
* src/process.c (create_process) [WINDOWSNT]: ... to here, after the
unblock_input() call.
---
 src/callproc.c | 7 ++-----
 src/lisp.h     | 6 ++++++
 src/process.c  | 2 +-
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/callproc.c b/src/callproc.c
index fa12d02..a011250 100644
--- a/src/callproc.c
+++ b/src/callproc.c
@@ -695,7 +695,7 @@ call_process (ptrdiff_t nargs, Lisp_Object *args, int filefd,
   unblock_input ();
 
   if (pid < 0)
-    report_file_errno ("Doing vfork", Qnil, child_errno);
+    report_file_errno (CHILD_SETUP_ERROR_DESC, Qnil, child_errno);
 
   /* Close our file descriptors, except for callproc_fd[CALLPROC_PIPEREAD]
      since we will use that to read input from.  */
@@ -1189,7 +1189,7 @@ exec_failed (char const *name, int err)
    executable directory by the parent.
 
    On GNUish hosts, either exec or return an error number.
-   On MS-Windows, either return a pid or signal an error.
+   On MS-Windows, either return a pid or return -1 and set errno.
    On MS-DOS, either return an exit status or signal an error.  */
 
 CHILD_SETUP_TYPE
@@ -1334,9 +1334,6 @@ child_setup (int in, int out, int err, char **new_argv, bool set_pgrp,
   /* Spawn the child.  (See w32proc.c:sys_spawnve).  */
   cpid = spawnve (_P_NOWAIT, new_argv[0], new_argv, env);
   reset_standard_handles (in, out, err, handles);
-  if (cpid == -1)
-    /* An error occurred while trying to spawn the process.  */
-    report_file_error ("Spawning child process", Qnil);
   return cpid;
 
 #else  /* not WINDOWSNT */
diff --git a/src/lisp.h b/src/lisp.h
index 08c6dbd..c7eb471 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4233,6 +4233,12 @@ extern void setup_process_coding_systems (Lisp_Object);
 #else
 # define CHILD_SETUP_TYPE int
 #endif
+#ifdef WINDOWSNT
+# define CHILD_SETUP_ERROR_DESC "Spawning child process"
+#else
+# define CHILD_SETUP_ERROR_DESC "Doing vfork"
+#endif
+
 extern CHILD_SETUP_TYPE child_setup (int, int, int, char **, bool, Lisp_Object);
 extern void init_callproc_1 (void);
 extern void init_callproc (void);
diff --git a/src/process.c b/src/process.c
index 2df51cf..b8b7a3e 100644
--- a/src/process.c
+++ b/src/process.c
@@ -2204,7 +2204,7 @@ create_process (Lisp_Object process, char **new_argv, Lisp_Object current_dir)
   unblock_input ();
 
   if (pid < 0)
-    report_file_errno ("Doing vfork", Qnil, vfork_errno);
+    report_file_errno (CHILD_SETUP_ERROR_DESC, Qnil, vfork_errno);
   else
     {
       /* vfork succeeded.  */
-- 
2.6.2.windows.1