emacs-27 ac3da1d: Handle project--files-in-directory finding no files better

[Dmitry Gutov]

branch: emacs-27
commit ac3da1dd9626bc475e78b18c0b438435790e8926
Author: Dmitry Gutov <address@hidden>
Commit: Dmitry Gutov <address@hidden>

    Handle project--files-in-directory finding no files better
    
    * lisp/progmodes/project.el (project--find-regexp-in-files):
    Signal user-error when passed an empty list of files.
    
    * lisp/progmodes/xref.el (xref-matches-in-files):
    Make sure FILES is not empty.
---
 lisp/progmodes/project.el | 2 ++
 lisp/progmodes/xref.el    | 1 +
 2 files changed, 3 insertions(+)

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index f467868..1f4cbe9 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -480,6 +480,8 @@ pattern to search for."
      nil)))
 
 (defun project--find-regexp-in-files (regexp files)
+  (unless files
+    (user-error "Empty file list"))
   (let ((xrefs (xref-matches-in-files regexp files)))
     (unless xrefs
       (user-error "No matches for: %s" regexp))
diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index 1a34456..c36a9bd 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1232,6 +1232,7 @@ IGNORES is a list of glob patterns for files to ignore."
   "Find all matches for REGEXP in FILES.
 Return a list of xref values.
 FILES must be a list of absolute file names."
+  (cl-assert (consp files))
   (pcase-let*
       ((output (get-buffer-create " *project grep output*"))
        (`(,grep-re ,file-group ,line-group . ,_) (car grep-regexp-alist))