bug#42136: 26.1.90; rgrep uses a directory that was not actually given

[Benjamin Riefenstahl]

Receipe:

* M-x make-directory RET "/tmp/cds_config" RET
* rgrep RET abc RET * RET /tmp/cds_c RET

Observed: rgrep searches in "/tmp/cds_config".

Expected: Error message that the directory "/tmp/cds_c" does not exist.
Alternatively a comfirmation question about the completion.

----

Long form of the use case:

I have two projects with similar names "cds_c" and "cds_config".  On
some of my machines both are checked out side-by-side, on some only one
of them is.  Today I called rgrep and gave ".../cds_c" as input for the
directory.  rgrep actually searched in ".../cds_config".  I only later
discovered that that was what happened, initially I thought my pattern
was just not found in my project "cds_c".  I would have expected that
rgrep would complain that the directory does not exist, either during
input or later, instead of silently completing the directory name.

The directory name that was searched is of course in the grep buffer,
but the grep buffer looks like this:

---------
-*- mode: grep; default-directory: "/tmp/cds_config/" -*-
Grep started at Tue Jun 30 12:25:32

find . -type d \( -path \*/CVS -o -path \*/.svn -o -path \*/\{arch\} -o
-path \*/.hg -o -path \*/_darcs -o -path \*/.git -o -path \*/.bzr -o
-path \*/.metadata -o -path \*/.metadata.old -o -path \*/maven-targets
-o -path \*/build -o -path \*/target -o -path \*/projekktor -o -path
\*/node_modules \) -prune -o \! -type d \( -name .\#\* -o -name \*.cmti
-o -name \*.cmt -o -name \*.annot -o -name \*.cmi -o -name \*.cmxa -o
-name \*.cma -o -name \*.cmx -o -name \*.cmo -o -name \*.o -o -name \*\~
-o -name \*.bin -o -name \*.lbin -o -name \*.so -o -name \*.a -o -name
\*.ln -o -name \*.blg -o -name \*.bbl -o -name \*.elc -o -name \*.lof -o
-name \*.glo -o -name \*.idx -o -name \*.lot -o -name \*.fmt -o -name
\*.tfm -o -name \*.class -o -name \*.fas -o -name \*.lib -o -name \*.mem
-o -name \*.x86f -o -name \*.sparcf -o -name \*.dfsl -o -name \*.pfsl -o
-name \*.d64fsl -o -name \*.p64fsl -o -name \*.lx64fsl -o -name
\*.lx32fsl -o -name \*.dx64fsl -o -name \*.dx32fsl -o -name \*.fx64fsl
-o -name \*.fx32fsl -o -name \*.sx64fsl -o -name \*.sx32fsl -o -name
\*.wx64fsl -o -name \*.wx32fsl -o -name \*.fasl -o -name \*.ufsl -o
-name \*.fsl -o -name \*.dxl -o -name \*.lo -o -name \*.la -o -name
\*.gmo -o -name \*.mo -o -name \*.toc -o -name \*.aux -o -name \*.cp -o
-name \*.fn -o -name \*.ky -o -name \*.pg -o -name \*.tp -o -name \*.vr
-o -name \*.cps -o -name \*.fns -o -name \*.kys -o -name \*.pgs -o -name
\*.tps -o -name \*.vrs -o -name \*.pyc -o -name \*.pyo \) -prune -o
-type f ! -name '*[~#]*' ! -name TAGS ! -name '*.patch' ! -name '*.jpg'
! -name '*.log' ! -name '*.log.*' \( -name \* \) -print0 | xargs -0 -e
grep --color -i -nH -e abc

Grep finished with no matches found at Tue Jun 30 12:25:32
---------

And of course I was concentrating on the bottom where it says "no
matches", not at all on the top of the buffer to confirm that rgrep
actually did what I just told it to do.

I tried to find if the behaviour was somehow customizable, but it seems
not.

----

In GNU Emacs 26.1.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2018-11-22 built on riefenstahl-thinkpad
Repository revision: 93242b14769ed40ae58e89d0ea45df8872f59869
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description:     Ubuntu 16.04.6 LTS

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
  global-magit-file-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  desktop-save-mode: t
  display-time-mode: t
  diff-auto-refine-mode: t
  delete-selection-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
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