gazelle can modify a "# gazelle:ignore" BUILD file

[treaster]

Running gazelle to regenerate a BUILD file containing # gazelle:ignore can modify the existing file. It appears that the changes are only reordering/cleanup of the existing rules, with no structural changes. However, the docs say "# gazelle:ignore in a BUILD file will instruct gazelle to leave the file alone.", which isn't true.

One possible fix would be to update the documentation for accuracy.

Another possible fix would be to avoid writing out anything when the ignore directive appears.

I can see arguments for both the cleanup mode (the existing behavior) and the strict non-intervention mode (what the documentation says). I think either of my proposals would address the problem.

The ideal solution might be to use the strict mode by default, then also provide a --cleanup mode which executes the existing cleanup behavior.

To reproduce

mkdir -p gazelle_test/code
cd gazelle_test/
echo "package main\nfunc main() {}" > code/main.go
print "# gazelle:ignore\n\n\n# some comment" > BUILD.orig
print "# gazelle:ignore\n\n\n# some comment" > BUILD
gazelle --repo_root=. --go_prefix=code
diff code/BUILD.orig code/BUILD

produces:

3,4c3
< 
< # some comment
\ No newline at end of file
---
> # some comment

i.e. some whitespace was removed. Other changes are also possible, such as reordering of build rule attributes.

Random implementation thought

One possible approach to implementing the strict mode might be to use something like this in gazelle's main.go where MergeWithExisting() is called.
https://github.com/bazelbuild/rules_go/blob/master/go/tools/gazelle/gazelle/main.go#L101

f, err := merger.MergeWithExisting(f, existingFilePath)
switch err.(type) {
    case nil:
        // write out the generated file as usual
    case GazelleIgnoreErr:  // "# gazelle:ignore" was seen
        // cancel further processing of this BUILD, but continue
        // the loop to process other BUILDs.
        continue  
    case error:
        return err // interrupt the loop and cancel program execution          
}

[treaster]

I discovered that comments inside a srcs block will also be removed even when # gazelle:ignore appears in the file. For example:

# gazelle:ignore
...
srcs = [
    "foo.go",
    # "bar.go",
    "baz.go",
]

becomes

# gazelle:ignore
...
srcs = [
    "foo.go",
    "baz.go",
]

[pmbethe09]

Seems we should fix or remove this feature -- I don't have any cycles right now, but could review someone else's changes.

[jayconrod]

I'll take a look at this.

[treaster]

Thanks for making this fix, Jay!