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Re: [Emacs-diffs] master bb591f139f: Enhance CC Mode's fontification, et

From: João Távora
Subject: Re: [Emacs-diffs] master bb591f139f: Enhance CC Mode's fontification, etc., of unterminated strings.
Date: Tue, 22 May 2018 20:21:25 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Hi Alan,

Alan Mackenzie <address@hidden> writes:

> electric-tests.el is anything but straightforward to read.

lol, sorry I couldn't quite make the 20000+LOC standards of cc-mode.el

No really, kidding, <wipes tears>, that file needs macros because it
defines almost 500 tests with very subtle variations between them. You
tripped one of them, and I think we're both glad you did (regardless of
who is at fault: test or c++-mode)

> The test referred to above is generated by a nest of two or three
> macros, somehow, and it is not obvious what buffer operations were
> generated by these macros, and how they triggered a newly introduced bug
> in C++ Mode.  The comments in the file are too sparse to help.

Here's how it works: There's only one macro for electric-pair tests,
aptly named define-electric-pair-test.

In that file, find the `define-electric-pair-test' that most closely
matches the test failure, in this case its:

   (define-electric-pair-test autowrapping-5
     "foo" "\"" :expected-string "\"foo\"" :expected-point 2
     :fixture-fn #'(lambda ()
                     (electric-pair-mode 1)
                     (mark-sexp 1)))

now go to the end of the expression and type M-x
pp-macroexpand-last-sexp. It should be easy to find your failing test,
defined in terms of `ert-deftest', in a list of 6 tests. Here it is:

  (ert-deftest electric-pair-autowrapping-5-at-point-2-in-c++-mode-in-strings 
  "With |\"foo\"|, try input \" at point 2. Should become |\"\"foo\"\"| and 
point at 3"
               (electric-pair-test-for "\"foo\"" 2 34 "\"\"foo\"\"" 3 'c++-mode 
                                       #'(lambda nil
                                           (electric-pair-mode 1)
                                           (mark-sexp 1))))

Now M-x edebug-defun this form straight in the *Pp Macroexpand Output*
buffer, and M-x edebug-defun the `electric-pair-test-for' defun,
too. Now run the test:

  M-x ert RET electric-pair-autowrapping-5-at-point-2-in-c++-mode-in-strings RET

As you step through the code, you'll eventually land on that lambda
which calls mark-sexp and hints, along with the name, that this is a
region-autowrapping test. This is why it expects, for a single character
of input, that two quotes are inserted in the buffer instead of
one. The test passes in my 26.1 as you probably already knew.

Good luck hunting the bug and let me know if you have more problems.


PS: you could also have used:

   M-x ert-describe-test RET 

Which would have rendered a nice docstring

    electric-pair-autowrapping-5-at-point-2-in-c++-mode-in-strings is a
    test defined in `electric-tests.elc'.
    With |"foo"|, try input " at point 2. Should become |""foo""| and point at 3

Though, admittedly, this is misleading for the "autowrapping" tests,
since it doesn't tell you about the "mark-sexp" region-making
command. Also not immediatly clear perhaps it that the | are buffer

Ideally, it should read read

  With |"foo"|, at point 2, (mark-sexp 1) and try input ".
  Should become |""foo""| and point at 3

I will try to fix this in master.

Also M-x ert-find-test-other-window could have helped you, but it
doesn't (brings me to the beginning of the file, which isn't helpful). I
don't know why, does anyone?

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