Fix flymake to work with my Emacs, and hopefully not break others.

tools/emacs/flymake-chromium.el

 ;; Copyright (c) 2011 The Chromium Authors. All rights reserved.
 ;; Use of this source code is governed by a BSD-style license that can be
 ;; found in the LICENSE file.
 
 ;; Set up flymake for use with chromium code.  Uses ninja (since none of the
 ;; other chromium build systems have latency that allows interactive use).
 ;;
 ;; Requires a modern emacs (GNU Emacs >= 23) and that gyp has already generated
 ;; the build.ninja file(s).  See defcustoms below for settable knobs.
 
 
 (require 'flymake)
 
 (defcustom cr-flymake-ninja-build-file "out/Debug/build.ninja"
   "Relative path from chromium's src/ directory to the
   build.ninja file to use.")
 
 (defcustom cr-flymake-ninja-executable "ninja"
   "Ninja executable location; either in $PATH or explicitly given.")
 
+(defun cr-flymake-absbufferpath ()
+  "Return the absolute path to the current buffer. On some
+  Emacsen, buffer-file-truename is not absolute but rather uses a

[Ami GONE FROM CHROMIUM, 2011/12/08 16:17:01]

I believe this behavior is in fact the case for all emacsen.

[Ami GONE FROM CHROMIUM, 2011/12/08 19:27:49]

Remove the second sentence of the docstring.

[Jói, 2011/12/08 20:46:16]

Done.

+  path relative to the user's home dir (with ~)."
+  (when buffer-file-truename
+      (expand-file-name buffer-file-truename)))
+
 (defun cr-flymake-chromium-src ()
   "Return chromium's src/ directory, or nil on failure."
-  (locate-dominating-file buffer-file-truename cr-flymake-ninja-build-file))
+  (let ((srcdir (locate-dominating-file
+                 (cr-flymake-absbufferpath) cr-flymake-ninja-build-file)))
+    (when srcdir (expand-file-name srcdir))))

[Ami GONE FROM CHROMIUM, 2011/12/08 19:27:49]

You don't need this when (and thus the above let) b/c cr-flymake-absbufferpath
already has a guard.

[Jói, 2011/12/08 20:46:16]

locate-dominating-file is fine with a nil and then returns a nil, but it returns
a ~ prefixed path for my config when it's non-nil, so I need expand-file-name so
we can do the prefix checking correctly.

Since expand-file-name errors out if you pass it a nil, I think I still need the
guard here.

[Ami GONE FROM CHROMIUM, 2011/12/08 20:49:16]

I was mis-reading the code before (thinking you're passing srcdir to
cr-flymake-absbufferpath).  You're right.

 
 (defun cr-flymake-string-prefix-p (prefix str)
   "Return non-nil if PREFIX is a prefix of STR (23.2 has string-prefix-p but
   that's case insensitive and also 23.1 doesn't have it)."
   (string= prefix (substring str 0 (length prefix))))
 
 (defun cr-flymake-current-file-name ()
   "Return the relative path from chromium's src/ directory to the
   file backing the current buffer or nil if it doesn't look like
   we're under chromium/src/."
   (when (and (cr-flymake-chromium-src)
              (cr-flymake-string-prefix-p
-              (cr-flymake-chromium-src) buffer-file-truename))
-    (substring buffer-file-truename (length (cr-flymake-chromium-src)))))
+              (cr-flymake-chromium-src) (cr-flymake-absbufferpath)))
+    (substring (cr-flymake-absbufferpath) (length (cr-flymake-chromium-src)))))

[Ami GONE FROM CHROMIUM, 2011/12/08 16:17:01]

I don't understand the need for these abspath changes.
locate-dominating-file works fine for me with ~-abreviated paths, so this
function correctly returns the relative path from the src root to the current
buffer's file.

Can you say more about what triggered the need for this change?  Specifically
what OS/emacs version are you on, and can you give me an example file you were
editing that caused this function to barf (and how, if you have it)?
Happy to pair-debug over IM when I'm in the office.

 
 (defun cr-flymake-from-build-to-src-root ()
   "Return a path fragment for getting from the build.ninja file to src/."
   (replace-regexp-in-string
    "[^/]+" ".."
    (substring
     (file-name-directory
      (file-truename (or (and (cr-flymake-string-prefix-p
                               "/" cr-flymake-ninja-build-file)
                              cr-flymake-ninja-build-file)
@@ skipping 13 matching lines @@
           (list "-C"
                 (concat (cr-flymake-chromium-src)
                         (file-name-directory cr-flymake-ninja-build-file))
                 (concat (cr-flymake-from-build-to-src-root)
                         (cr-flymake-current-file-name) "^")))))
 
 (defun cr-flymake-kick-off-check-after-save ()
   "Kick off a syntax check after file save, if flymake-mode is on."
   (when flymake-mode (flymake-start-syntax-check)))
 
-(defadvice next-error (around cr-flymake-next-error activate)

[Ami GONE FROM CHROMIUM, 2011/12/08 16:17:01]

This change is wrong - that particular arg to defadvice is the _name_ of the
advice, not the function being advised (that'd be next-error, defadvice's first
arg).
(update CL description after reverting this)

+(defadvice next-error (around flymake-next-error activate)
   "If flymake has something to say, let it say it; otherwise
    revert to normal next-error behavior."
   (if (not flymake-err-info)
       (condition-case msg
           ad-do-it
         (error (message "%s" (prin1-to-string msg))))
     (flymake-goto-next-error)
     ;; copy/pasted from flymake-display-err-menu-for-current-line because I
     ;; couldn't find a way to have it tell me what the relevant error for this
     ;; line was in a single call:
@@ skipping 23 matching lines @@
       (kill-local-variable 'flymake-allowed-file-name-masks))))
 
 (add-hook 'find-file-hook 'cr-flymake-find-file 'append)
 (add-hook 'after-save-hook 'cr-flymake-kick-off-check-after-save)
 
 ;; Show flymake infrastructure ERRORs in hopes of fixing them.  Set to 3 for
 ;; DEBUG-level output from flymake.el.
 (setq flymake-log-level 0)
 
 (provide 'flymake-chromium)