tests/test-editor-filename.t

editor: use an unambiguous path suffix for editor files

Changes the API of `ui.edit()` to take an optional `action` argument,
which is used when constructing the suffix of the temp file.
Previously, it was possible to set the suffix by specifying a `suffix` to the
optional `extra` dict that was passed to `ui.edit()`, but the goal is to
drop support for `extra.suffix` and make `action` a required argument.
To this end, `ui.edit()` now yields a `develwarn()` if `action` is not set
or if `extra.suffix` is set.

I updated all calls to `ui.edit()` I could find in `hg-crew` to specify the
appropriate `action`. This means that when creating a commit, instead
of the path to the editor file being something like:

`/tmp/hg-editor-XXXXXX.txt`

it is now something like:

`/tmp/hg-editor-XXXXXX.commit.hg.txt`

Some editors (such as Atom) make it possible to statically define a [TextMate]
grammar for files with a particular suffix. For example, because Git reliably
uses `.git/COMMIT_EDITMSG` and `.git/MERGE_MSG` as the paths for commit-type
messages, it is trivial to define a grammar that is applied when files of
either name are opened in Atom:

https://github.com/atom/language-git/blob/v0.19.1/grammars/git%20commit%20message.cson#L4-L5

Because Hg historically used a generic `.txt` suffix, it was much harder to
disambiguate whether a file was an arbitrary text file as opposed to one
created for the specific purpose of authoring an Hg commit message.

This also makes it easier to add special support for `histedit`, as it has its own
suffix that is distinct from a commit:

`/tmp/hg-histedit-XXXXXX.histedit.hg.txt`

Test Plan:
Added an integration test: `test-editor-filename.t`.

Manually tested: ran `hg ci --amend` for this change and saw that it
used `/tmp/hg-editor-ZZjcz0.commit.hg.txt` as the path instead of
`/tmp/hg-editor-ZZjcz0.txt` as the path.

Verified `make tests` passes.

Differential Revision: https://phab.mercurial-scm.org/D464

Test temp file used with an editor has the expected suffix.

  $ hg init

Create an editor that writes its arguments to stdout and set it to $HGEDITOR.

  $ cat > editor.sh << EOF
  > #!/bin/bash
  > echo "\$@"
  > exit 1
  > EOF
  $ chmod +x editor.sh
  $ hg add editor.sh
  $ HGEDITOR=$TESTTMP/editor.sh
  $ export HGEDITOR

Verify that the path for a commit editor has the expected suffix.

  $ hg commit
  *.commit.hg.txt (glob)
  abort: edit failed: editor.sh exited with status 1
  [255]

Verify that the path for a histedit editor has the expected suffix.

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > histedit=
  > EOF
  $ hg commit --message 'At least one commit for histedit.'
  $ hg histedit
  *.histedit.hg.txt (glob)
  abort: edit failed: editor.sh exited with status 1
  [255]