Fix 'ffap-string-at-point' under 'ffap-file-name-with-spaces'

* lisp/ffap.el (ffap-file-name-with-spaces): Doc fix.
(ffap-string-at-point): Don't reject '~foo/' and 'd:/bar' file
names when 'ffap-file-name-with-spaces' is non-nil.

* test/lisp/ffap-tests.el (ffap-test-with-spaces): Add tests, and
fix expected results to not strip Windows drive letters.

lisp/ffap.el

@@ -1140,7 +1140,7 @@ The arguments CHARS, BEG and END are handled as described in
   "Last string returned by the function `ffap-string-at-point'.")
 
 (defcustom ffap-file-name-with-spaces nil
-  "If non-nil, enable looking for paths with spaces in `ffap-string-at-point'.
+  "If non-nil, allow file names with spaces in `ffap-string-at-point'.
 Enabling this variable may lead to `find-file-at-point' guessing
 wrong more often when trying to find a file name intermingled
 with normal text, but can be useful when working on systems that
@@ -1286,10 +1286,16 @@ return an empty string, and set `ffap-string-at-point-region' to `(1 1)'."
 	          (if (and ffap-file-name-with-spaces
 			   (memq mode '(nil file)))
 		      (when (setq dir-separator (ffap-dir-separator-near-point))
-		        (while (re-search-backward
+                        (let ((dirsep-re (regexp-quote dir-separator))
-			        (regexp-quote dir-separator)
+                              (line-beg (line-beginning-position)))
-			        (line-beginning-position) t)
+		          (while (re-search-backward dirsep-re line-beg t)
-		          (goto-char (match-beginning 0))))
+		            (goto-char (match-beginning 0)))
+                          (if (and (looking-at dirsep-re)
+                                   (looking-back
+                                    ;; Either "~[USER]" or drive letter.
+                                    "\\(~[[:graph:]]*\\|[a-zA-Z]:\\)"
+                                    line-beg))
+                              (goto-char (match-beginning 0)))))
 		    (skip-chars-backward (car args))
 		    (skip-chars-forward (nth 1 args) pt))
 		  (point))))

test/lisp/ffap-tests.el

@@ -105,7 +105,7 @@ left alone when opening a URL in an external browser."
     (with-temp-buffer
       (insert string)
       (goto-char (point-min))
-      (forward-char 10)
+      (forward-char 3)
       (ffap-string-at-point))))
 
 (ert-deftest ffap-test-with-spaces ()
@@ -113,7 +113,7 @@ left alone when opening a URL in an external browser."
    (equal
     (ffap-test-string
      t "c:/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program here.txt")
-    "/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program here.txt"))
+    "c:/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program here.txt"))
   (should
    (equal
     (ffap-test-string
@@ -122,23 +122,39 @@ left alone when opening a URL in an external browser."
   (should
    (equal
     (ffap-test-string
-     t "c:/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program Files/Hummingbird/")
+     t "z:/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program Files/Hummingbird/")
-    "/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program Files/Hummingbird/"))
+    "z:/Program Files/Open Text Evaluation Media/Open Text Exceed 14 x86/Program Files/Hummingbird/"))
   (should
    (equal
     (ffap-test-string
      t "c:\\Program Files\\Open Text Evaluation Media\\Open Text Exceed 14 x86\\Program Files\\Hummingbird\\")
-    "\\Program Files\\Open Text Evaluation Media\\Open Text Exceed 14 x86\\Program Files\\Hummingbird\\"))
+    "c:\\Program Files\\Open Text Evaluation Media\\Open Text Exceed 14 x86\\Program Files\\Hummingbird\\"))
   (should
    (equal
     (ffap-test-string
-     t "c:\\Program Files\\Freescale\\CW for MPC55xx and MPC56xx 2.10\\PowerPC_EABI_Tools\\Command_Line_Tools\\CLT_Usage_Notes.txt")
+     t "d:\\Program Files\\Freescale\\CW for MPC55xx and MPC56xx 2.10\\PowerPC_EABI_Tools\\Command_Line_Tools\\CLT_Usage_Notes.txt")
-    "\\Program Files\\Freescale\\CW for MPC55xx and MPC56xx 2.10\\PowerPC_EABI_Tools\\Command_Line_Tools\\CLT_Usage_Notes.txt"))
+    "d:\\Program Files\\Freescale\\CW for MPC55xx and MPC56xx 2.10\\PowerPC_EABI_Tools\\Command_Line_Tools\\CLT_Usage_Notes.txt"))
   (should
    (equal
     (ffap-test-string
      t "C:\\temp\\program.log on Windows or /var/log/program.log on Unix.")
-    "\\temp\\program.log")))
+    "C:\\temp\\program.log"))
+  (should
+   (equal
+    (ffap-test-string t "~/tmp/")
+    "~/tmp/"))
+  (should
+   (equal
+    (ffap-test-string nil "~/tmp/")
+    "~/tmp/"))
+  (should
+   (equal
+    (ffap-test-string t "~abc123_áè/foo")
+    "~abc123_áè/foo"))
+  (should
+   (equal
+    (ffap-test-string t "c:/Program Files/my program.exe and here's more text")
+    "c:/Program Files/my program.exe")))
 
 (ert-deftest ffap-test-no-newlines ()
   (should-not