config: Added the --show-origin and --for-file options

* config: Added the --show-origin and --for-file options.
* config: Support annex.numcopies and annex.mincopies.

There is a little bit of redundancy here with other code elsewhere that
combines the various configs and selects which to use. But really only
for the special case of annex.numcopies, which is a git config that does
not override the annex branch setting and for annex.mincopies, which does
not have a git config but does have gitattributes settings as well as the
annex branch setting.

That seems small enough, and unlikely enough to grow into a mess that it was
worth supporting annex.numcopies and annex.mincopies in git-annex config
--show-origin. Because these settings are a prime thing that someone might
get confused about and want to know where they were configured.

And, it followed that git-annex config might as well support those two
for --set and --get as well. While this is redundant with the speclialized
commands, it's only a little code and it makes it more consistent.

Note that --set does not have as nice output as numcopies/mincopies
commands in some special cases like setting to 0 or a negative number.
It does avoid setting to a bad value thanks to the smart
constructors (eg configuredNumCopies).

As for other git-annex branch configurations that are not set by git-annex
config, things like trust and wanted that are specific to a repository
don't map to a git config name, so don't really fit into git-annex config.
And they are only configured in the git-annex branch with no local override
(at least so far), so --show-origin would not be useful for them.

Sponsored-by: Dartmouth College's DANDI project

doc/git-annex-config.mdwn

@@ -10,6 +10,8 @@ git annex config --get name
 
 git annex config --unset name
 
+git annex config --show-origin name
+
 # DESCRIPTION
 
 Set or get configuration settings stored in the git-annex branch.
@@ -29,6 +31,47 @@ looks for these.
 
 # SUPPORTED SETTINGS
 
+* `annex.numcopies`
+
+  Tells git-annex how many copies it should preserve of files, over all
+  repositories. The default is 1.
+
+  When git-annex is asked to drop a file, it first verifies that the
+  number of copies can be satisfied among all the other
+  repositories that have a copy of the file.
+  
+  In unusual situations, involving special remotes that do not support
+  locking, and concurrent drops of the same content from multiple
+  repositories, git-annex may violate the numcopies setting. It still
+  guarantees at least 1 copy is preserved. This can be configured by
+  setting annex.mincopies.
+
+  This is the same setting that the [[git-annex-numcopies]](1) command
+  configures. It can be overridden on a per-file basis
+  by the annex.numcopies setting in `.gitattributes` files.
+
+* `annex.mincopies`
+
+  Tells git-annex how many copies it is required to preserve of files, 
+  over all repositories. The default is 1.
+
+  This supplements the annex.numcopies setting. 
+  In unusual situations, involving special remotes that do not support
+  locking, and concurrent drops of the same content from multiple
+  repositories, git-annex may violate the numcopies setting.
+  In these unusual situations, git-annex ensures that the number of copies
+  never goes below mincopies.
+  
+  It is a good idea to not only rely on only setting mincopies. Set
+  numcopies as well, to a larger number, and keep mincopies at the
+  bare minimum you're comfortable with. Setting mincopies to a large
+  number, rather than setting numcopies will in some cases prevent
+  droping content in entirely safe situations.
+
+  This is the same setting that the [[git-annex-mincopies]](1) command
+  configures. It can be overridden on a per-file basis
+  by the annex.mincopies setting in `.gitattributes` files.
+
 * `annex.largefiles`
 
   Used to configure which files are large enough to be added to the annex.
@@ -143,6 +186,24 @@ looks for these.
 
   Unset a value.
 
+* `--show-origin name`
+
+  Explain where the value is configured, whether in the git-annex branch,
+  or in a `git config` file, or `.gitattributes` file. When a value is
+  configured in multiple places, displays the place and the value that
+  will be used.
+
+  Note that the parameter can be the name of one of the settings listed
+  above, but also any other configuration setting supported by git-annex.
+  For example, "annex.backend" cannot be set in the git-annex branch, but
+  it can be set in `.gitattributes` or `git config` and this option can
+  explain which setting will be used for it.
+
+* `--for-file file`
+
+  Can be used in combination with `--show-origin` to specify what
+  filename to check for in `.gitattributes`.
+
 * Also the [[git-annex-common-options]](1) can be used.
 
 # EXAMPLE

doc/git-annex-mincopies.mdwn

@@ -39,6 +39,7 @@ droping content in entirely safe situations.
 
 [[git-annex]](1)
 [[git-annex-numcopies]](1)
+[[git-annex-config]](1)
 
 # AUTHOR
 

doc/git-annex-numcopies.mdwn

@@ -36,6 +36,7 @@ using [[git-annex-mincopies]](1)
 
 [[git-annex]](1)
 [[git-annex-mincopies]](1)
+[[git-annex-config]](1)
 
 # AUTHOR
 

doc/todo/a_way_to_figure_out_the_origin_of_largefiles.mdwn

@@ -6,3 +6,5 @@ I guess the same functionality might be useful for some other options which coul
 
 [[!meta author=yoh]]
 [[!tag projects/dandi]]
+
+> [[done]] --[[Joey]]

doc/todo/a_way_to_figure_out_the_origin_of_largefiles/comment_2_6bfe8e1b6b2c3334803d8a6676862e8a._comment

@@ -0,0 +1,20 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 2"""
+ date="2023-06-12T20:08:40Z"
+ content="""
+I think it makes sense to have a command that displays the value of a
+config that will be used, and where that value is configured. I've implemented 
+`git-annex config --show-origin` to do that.
+
+For example:
+
+	% git-annex config --show-origin annex.largefiles
+	  annex.largefiles may be configured in gitattributes. Pass --for-file= with a filename to check
+	branch:git-annex	exclude=*.c
+	% git-annex config --show-origin annex.largefiles --for-file=foo
+	gitattributes	largerthan=100kb
+	% git config annex.largefiles oops
+	% git-annex config --show-origin annex.largefiles --for-file=foo
+	file:.git/config	oops
+"""]]