squash! bash prompt: fix here document indentation in interactive rebase test

CHANGE SUBJECT TO:

bash prompt: use 'write_script' helper in interactive rebase test

Helped-by: Jeff King <peff@peff.net>
completion, bash prompt: move __gitdir() tests to completion test suite

Currently __gitdir() is duplicated in the git completion and prompt
scripts, while its tests are in the prompt test suite.  This patch
series is about to change __git_ps1() in a way that it won't need
__gitdir() anymore and __gitdir() will be removed from the prompt
script.

So move all __gitdir() test from the prompt test suite over to the
completion test suite.  Update the setup tests so that they perform
only those steps that are necessary for each test suite.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: add a test for symbolic link symbolic refs

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: return early from __git_ps1() when not in a git repository

... to gain one level of indentation for the bulk of the function.

(The patch looks quite unreadable, you'd better check it with 'git
diff -w'.)

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: run 'git rev-parse --git-dir' directly instead of __gitdir()

__git_ps1() finds out the path to the repository by using the
__gitdir() helper function.  __gitdir() is basically just a wrapper
around 'git rev-parse --git-dir', extended with support for
recognizing a remote repository given as argument, to use the path
given on the command line, and with a few shortcuts to recognize a git
repository in cwd or at $GIT_DIR quickly without actually running 'git
rev-parse'.  However, the former two is only necessary for the
completion script but makes no sense for the bash prompt, while the
latter shortcuts are performance optimizations __git_ps1() can do
without (they just avoid the overhead of fork()+exec()ing a git
process).

Run 'git rev-parse --git-dir' directly in __git_ps1(), because it will
allow this patch series to combine several $(git rev-parse ...)
command substitutions in the main code path, and the overall
performance benefit will far outweigh the loss of those few shortcuts
in __gitdir().  Furthermore, since __gitdir() is not needed anymore
for the prompt, remove it from the prompt script finally eliminating
its duplication between the prompt and completion scripts.  Also
remove the comment from the completion script warning about this code
duplication.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: use bash builtins to find out rebase state

During an ongoing interactive rebase __git_ps1() finds out the name of
the rebased branch, the total number of patches and the number of the
current patch by executing a '$(cat .git/rebase-merge/<FILE>)' command
substitution for each.  That is not quite the most efficient way to
read single line single word files, because it imposes the overhead of
fork()ing a subshell and fork()+exec()ing 'cat' several times.

Use the 'read' bash builtin instead to avoid those overheads.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: use bash builtins to find out current branch

__git_ps1() runs the '$(git symbolic-ref HEAD)' command substitution
to find out whether we are on a branch and to find out the name of
that branch.  This imposes the overhead of fork()ing a subshell and
fork()+exec()ing a git process.

Since HEAD is in most cases a single-line file and the symbolic ref
format is quite simple to recognize and parse, read and parse it using
only bash builtins, thereby sparing all that fork()+exec() overhead.
However, HEAD can also be a symlink symbolic ref (due to
'core.preferSymlinkRefs'), so do this only if HEAD is not a symlink.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
fixup! bash prompt: use bash builtins to find out current branch
bash prompt: use bash builtins to get detached HEAD abbrev. object name

When describing a detached HEAD according to the $GIT_PS1_DESCRIBE
environment variable fails, __git_ps1() runs the '$(cut -c1-7
.git/HEAD)' command substitution to put the 7 hexdigits abbreviated
commit object name in the prompt.  This imposes the overhead of
fork()ing a subshell and fork()+exec()ing 'cut'.

Thanks to the previous patch at this point the contents of HEAD has
already been read into a variable, so we can get the 7 hexdigits using
only parameter expansions, sparing the fork()+exec() overhead.

Since zsh doesn't implement substring expansion we can't just use
${head:0:7}, hence the "remove everything except the first 7 chars"
parameter expansion combination.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: combine 'git rev-parse' executions

From the four '$(git rev-parse --<opt>)' command substitutions
__git_ps1() executes three in its main code path:

 - the first to get the path to the .git directory ('--git-dir'),
 - the second to check whether we're inside the .git directory
   ('--is-inside-git-dir'),
 - and the last, depending on the results of the second, either
   * to check whether it's a bare repo ('--is-bare-repository'), or
   * to check whether inside a work tree ('--is-inside-work-tree').

Naturally, this imposes the overhead of fork()ing three subshells and
fork()+exec()ing three git commands.

Combine these four 'git rev-parse' queries into one and use bash
parameter expansions to parse the combined output, i.e. to separate
the path to the .git directory from the true/false of
'--is-inside-git-dir', etc.  This way we can eliminate two of the
three subshells and git commands.

The whole series speeds up the bash prompt on Windows/MSysGit
considerably.  Here are some timing results in two scenarios, repeated
10 times:

At the top of the work tree, before:

    $ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done

    real    0m1.716s
    user    0m0.301s
    sys     0m0.772s

  After:

    real    0m0.686s
    user    0m0.075s
    sys     0m0.287s

In a subdirectory, during rebase, stash status indicator enabled,
before:

    real    0m3.557s
    user    0m0.495s
    sys     0m1.767s

  After:

    real    0m0.702s
    user    0m0.045s
    sys     0m0.409s

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: use bash builtins to check stash state

When the environment variable $GIT_PS1_SHOWSTASHSTATE is set
__git_ps1() checks the presence of stashes by running 'git rev-parse
--verify refs/stash'.  This command not only checks that the
'refs/stash' ref exists but also, well, verifies that it's a valid
ref.

However, we don't need to be that thorough for the bash prompt.  We
can omit that verification and only check whether 'refs/stash' exists
or not.  Since 'git pack-refs' never packs 'refs/stash', it's a matter
of checking the existence of a ref file.  Perform this check using
only bash builtins to spare the overhead of fork()+exec()ing a git
process.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: avoid command substitution when checking for untracked files

When enabled, the bash prompt can indicate the presence of untracked
files with a '%' sign.  __git_ps1() checks for untracked files by running the
'$(git ls-files --others --exclude-standard)' command substitution,
and displays the indicator when there is no output.

Avoid this command substitution by additionally passing
'--error-unmatch *', and checking the command's return value.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
bash prompt: avoid command substitution when finalizing gitstring

Before setting $PS1, __git_ps1() uses a command substitution to
redirect the output from a printf into a variable.  Spare the overhead
of fork()ing a subshell by using 'printf -v <var>' to directly assign
the output to a variable.

zsh's printf doesn't support the '-v <var>' option, so stick with the
command substitution when under zsh.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>