Opening HTML file with nXhtml produces error with flymake - emacs

Question

When I open an HTML file with emacs (and nXhtml,) I get the following error from flymake:
Error (flymake): Flymake: Failed to launch syntax check process 'xml'
with args (val
/home/ABC/Downloads/capitals_flymake.html):
Searching for program: no such file or directory, xml. Flymake will be
switched OFF
I assume this means that I need to have a program installed that can be run at the command line with xml. However, I have not been able to find out what this program is in the documentation.
I am also currently using the following gist (with a modification suggested by one of the commenters to change equal to >=) to disable the Mumamo buffer filenames warning in my .emacs:
;; Workaround the annoying warnings:
;; Warning (mumamo-per-buffer-local-vars):
;; Already 'permanent-local t: buffer-file-name
(when
(and
(>= emacs-major-version 24)
(>= emacs-minor-version 2))
(eval-after-load "mumamo"
'(setq mumamo-per-buffer-local-vars
(delq 'buffer-file-name mumamo-per-buffer-local-vars))))
But, I am not sure if that is relevant.
How can I get flymake to work with nXhtml? I am currently on GNU Emacs 24.3.1.

Answer 1

I have this in my .emacs for live validating of XML and HTML, see if this would help.
(defun flymake-xml-init ()
(list "xmllint"
(list "--valid"
(flymake-init-create-temp-buffer-copy
'flymake-create-temp-inplace))))
(defun flymake-html-init ()
(let* ((temp-file (flymake-init-create-temp-buffer-copy
'flymake-create-temp-inplace))
(local-file (file-relative-name
temp-file
(file-name-directory buffer-file-name))))
(list "tidy" (list local-file))))
(add-to-list 'flymake-allowed-file-name-masks
'("\\.html$" flymake-html-init))
Also, re xml executable: it might be this one http://packages.ubuntu.com/quantal/amd64/xml2/filelist from how it looks... also you can try apt-file /usr/bin/xml (I'm not sure if apt-file is installed by default, if not, then apt-get install apt-file). Also, maybe this would help: http://www.emacswiki.org/emacs/FlyMake . I couldn't find any setting particular to nXhtml that does something to flymake.

Answer 2

The default program that flymake is told to use (xml) isn't installed on your computer, or its location isn't in your path. You need to tell flymake to use a different syntax checker just like #wvxvw said (see their answer for the code).
However, when you change the syntax checker, you may also need to tell flymake how that new checker will output error messages or else flymake won't know how to read the checker's output.
If your new checker program has an exit code other than 0 (which normally indicates an error) AND flymake didn't see anything that it recognized as error text, then flymake will throw a CFGERR and turn off.
From the flymake manual:
The following errors cause a warning message and switch flymake mode OFF for the buffer.
CFGERR : Syntax check process returned nonzero exit code, but no errors/warnings were reported. This indicates a possible configuration error (for example, no suitable error message patterns for the syntax check tool)
So what you need to do is tell flymake how to interpret the errors from your updated parser. You do this by adding a regex expression to a list that flymake will check against the output of your parser. Add something like this to your .emacs file:
(add-to-list
`flymake-err-line-patterns
'("at line \\([0-9]+\\) of \"\\([^ \n]+\\)\"$" 2 1 nil))
This will then tell flymake that if your parser generates output that matches the regex ("at line \\([0-9]+\\) of \"\\([^ \n]+\\)\"$") to identify it as an error message. The 2 1 nil tell flymake which group in the regex represents the file, line number, and column number, respectively. If the error message doesn't provide that information, then set that parameter to nil. In this example, the error message only identifies the file (second group) and line number (first group), so the column is set to nil.