src/save: Avoid writing CopyFile whenever possible

[mmirate]

If the file isn't plaintext, CopyFile remains mandatory.

If there are changes, write an inline unified-patch into a heredoc. If it's a new file, write its contents into a heredoc. If the new file has one or fewer lines, write an "echo" command (possibly with the -e flag in case of a file containing plaintext but no newlines).

This is essentially #46 but built into aconfmgr save.

Testing

This branch spent years on my backburner due to some frustrating bugs. Recently I fixed those, so that I have been using this branch on my collection of Arch computers. Doing so I've seen good effect at dredging up cruft, propagating good ideas, separating out things that are supposed to be different; all while keeping my intent clear and simple. I believe I've adapted the existing test cases to pass; but I did not yet try shoehorning multiline files into any of the existing test cases with which to exercise the full breadth of emitted heredocs; and I suspect that multiline text files who do not end with a newline, will still not be accurately captured.

Errata

• At one point during development I was using the -, as in <<-'EOF', to prepend tabs to the files or patches, to allow better indenting in the typical case where these fragments go inside if-statements etc; but I found it could not then accurately capture any file which was itself indented with tabs, so I dropped that feature, but it might be possible to add it back by checking for leading tab characters.

• With great difficulty I can fathom that inlining file contents into the config may be undesirable, especially as the line count of the inline content increases. The number of lines to tolerate looks like a bikeshed color. At the moment I've set no limit and no way for the user to add one. I know that adding a new command-line switch for this is suboptimal because it clutters the program's API surface. What about a new helper that manipulates a global variable?

Also Included

• One read into a global variable. I believe it would have had no adverse effect upon the status quo had it been allowed to persist. The new feature in this PR, by contrast, is broken unless either this variable is localized or the overwritten variable is renamed.

• The "Trim redundant blank parameters" loop would try to index into an empty args array, so I added a second loop-condition to prevent it from doing that. Maybe the fact that it tried to do that at all is evidence of something going wrong? I'm not sure.

• There are a few branches which have to write their contents to the $config_save_target themselves, leaving no $func etc to be written. Handling this contingency is what necessitates the nonemptiness check on $func.

[mmirate]

I know that adding a new command-line switch for this is suboptimal because it clutters the program's API surface. What about a new helper that manipulates a global variable?

Agreed; I would also imagine that some control on a path-by-path basis would be useful. Perhaps something in the shape of SetSaveMethod '*' auto?

I like it! It will take me a bit more time but it seems worthwhile to me. Bikeshed colors: the status quo would be called "copy" and my new functionality would be called "auto"?

[CyberShadow]

Bikeshed colors: the status quo would be called "copy" and my new functionality would be called "auto"?

Works for me!

[CyberShadow]

It will take me a bit more time but it seems worthwhile to me.

Happy to pick this up from here, BTW.

[mmirate]

It seems that this feature is somehow behaving differently under make ci versus under make testsuite-integration (which, unfortunately, I am unable to run on my machine - it hits a permission error trying to mkdir). In test/t/t-1_save-2_files-2_modified-2_skipchecksums_hitdiffsize.sh, make ci saves what I wrote - a printf to a CreateFile - but make testsuite-integration saves a patch of a GetPackageOriginalFile.