epg: Collect output lines sent to stderr

* epg.el (epg-context): Add new slot ERROR-OUTPUT.
(epg-error-output): New buffer-local variable.
(epg--start): Initialize epg-error-output.
(epg--process-filter): Record output lines sent to stderr, in
epg-error-output.
(epg-wait-for-completion): Copy epg-error-output to ERROR-OUTPUT
slot of context.
* epa-file.el (epa-file-insert-file-contents): On error, display
output sent to stderr.
(epa-file-write-region): Likewise.

lisp/ChangeLog

@@ -1,3 +1,16 @@
+2014-11-05  Daiki Ueno  <ueno@gnu.org>
+
+	* epg.el (epg-context): Add new slot ERROR-OUTPUT.
+	(epg-error-output): New buffer-local variable.
+	(epg--start): Initialize epg-error-output.
+	(epg--process-filter): Record output lines sent to stderr, in
+	epg-error-output.
+	(epg-wait-for-completion): Copy epg-error-output to ERROR-OUTPUT
+	slot of context.
+	* epa-file.el (epa-file-insert-file-contents): On error, display
+	output sent to stderr.
+	(epa-file-write-region): Likewise.
+
 2014-11-05  Eli Zaretskii  <eliz@gnu.org>
 
 	* jit-lock.el (jit-lock-stealth-fontify): Be tolerant to nil being

lisp/epa-file.el

@@ -162,6 +162,11 @@ encryption is used."
 	       (add-hook 'find-file-not-found-functions
 			 'epa-file--find-file-not-found-function
 			 nil t))
+	     (if (epg-context-error-output context)
+		 (epa-display-info
+		  (concat (format "Error while executing \"%s\":\n\n"
+				  epg-gpg-program)
+			  (epg-context-error-output context))))
 	     (signal 'file-error
 		     (cons "Opening input file" (cdr error)))))
           (set-buffer buf) ;In case timer/filter changed/killed it (bug#16029)!
@@ -257,6 +262,11 @@ If no one is selected, symmetric encryption will be performed.  "
       (error
        (if (setq entry (assoc file epa-file-passphrase-alist))
 	   (setcdr entry nil))
+       (if (epg-context-error-output context)
+	   (epa-display-info
+	    (concat (format "Error while executing \"%s\":\n\n"
+			    epg-gpg-program)
+		    (epg-context-error-output context))))
        (signal 'file-error (cons "Opening output file" (cdr error)))))
     (epa-file-run-real-handler
      #'write-region

lisp/epg.el

@@ -40,6 +40,7 @@
 (defvar epg-debug-buffer nil)
 (defvar epg-agent-file nil)
 (defvar epg-agent-mtime nil)
+(defvar epg-error-output nil)
 
 ;; from gnupg/include/cipher.h
 (defconst epg-cipher-algorithm-alist
@@ -210,7 +211,8 @@
   output-file
   result
   operation
-  pinentry-mode)
+  pinentry-mode
+  error-output)
 
 ;; This is not an alias, just so we can mark it as autoloaded.
 ;;;###autoload
@@ -639,7 +641,9 @@ callback data (if any)."
       (make-local-variable 'epg-agent-file)
       (setq epg-agent-file agent-file)
       (make-local-variable 'epg-agent-mtime)
-      (setq epg-agent-mtime agent-mtime))
+      (setq epg-agent-mtime agent-mtime)
+      (make-local-variable 'epg-error-output)
+      (setq epg-error-output nil))
     (with-file-modes 448
       (setq process (apply #'start-process "epg" buffer
 			   (epg-context-program context) args)))
@@ -673,7 +677,14 @@ callback data (if any)."
                       (if (and symbol
                                (fboundp symbol))
                           (funcall symbol epg-context string))
-                      (setq epg-last-status (cons status string))))
+                      (setq epg-last-status (cons status string)))
+		  ;; Record other lines sent to stderr.  This assumes
+		  ;; that the process-filter receives output only from
+		  ;; stderr and the FD specified with --status-fd.
+		  (setq epg-error-output
+			(cons (buffer-substring (point)
+						(line-end-position))
+			      epg-error-output)))
                 (forward-line)
                 (setq epg-read-point (point)))))))))
 
@@ -715,7 +726,10 @@ callback data (if any)."
       (redraw-frame))
   (epg-context-set-result-for
    context 'error
-   (nreverse (epg-context-result-for context 'error))))
+   (nreverse (epg-context-result-for context 'error)))
+  (with-current-buffer (process-buffer (epg-context-process context))
+    (setf (epg-context-error-output context)
+	(mapconcat #'identity (nreverse epg-error-output) "\n"))))
 
 (defun epg-reset (context)
   "Reset the CONTEXT."