Don't display bootstrap changelog warnings in --dry-run mode

[moxian]

Presently x.py displays "There have been changes to x.py since you last updated:" note only once when run normally, but on every invocation when run with --dry-run.
The disparity is not exactly intentonal, but just a historical accident.
It was made to be printed once in #117815 via storing .last-warned-change-id on disk in {config.out}/bootstrap (i.e. build/bootstrap) directory.
But that didn't quite work for --dry-run, since {config.out}/bootsrap points to build/tmp-dry-run/bootstrap which isn't created in dry-run mode, so file creation fails.
This got fixed in #118789 and now --dry-run does not save .last-warned-change-id at all. (Nor does it read it, since it cannot know to read from non-dry-run location)

This PR simply stops displaying the changelog altogether in --dry-run mode.

previous attempt (outdated)

This PR takes a different approach, and instead of not-writing the stamp in `--dry-run` mode it instead tries harder to yes-write it, and, specifically, creates `build/tmp-dry-run/bootstrap` directory to do so. If neccessary (i.e. if there are changes newer than the `change-id` stamp of config.toml to warn about). Note that `build/tmp-dry-run/` was *already* being created, so making an extra `boostrap` sub-folder should not meaningfully pollute the build dir.

(Apologies for the, perhaps, excessively wordy PR, I'm new to this)

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[moxian]

The current PR still makes us see the note twice - once for normal run, and once more for dry run, but that's not a big deal.

One alternative approach is to unify the location of .last-warned-change-id to be the same between dry-run and non-dry-run, but I'm not sure how to do that neatly. The obvious way is something like:

--- a/src/bootstrap/src/bin/main.rs
+++ b/src/bootstrap/src/bin/main.rs
@@ -151,7 +151,10 @@ fn check_version(config: &Config) -> Option<String> {
     let mut msg = String::new();

     let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap().change_id;
-    let warned_id_path = config.out.join("bootstrap").join(".last-warned-change-id");
+    // If we are in dry-run mode, try and recover the original config.out
+    // (i.e. the one without "tmp-dry-run" appended)
+    let base_path = if config.dry_run() { config.out.parent().unwrap() } else { config.out };
+    let warned_id_path = base_path.join("bootstrap").join(".last-warned-change-id");

     if let Some(mut id) = config.change_id {
         if id == latest_change_id {

but that looks extremely hacky, and probably not worth the gains.

[Kobzol]

Can't we just put an if condition around the print to avoid printing it in dry run mode altogether? Seems like that would be the easiest :)

[moxian]

Great idea, actually! Done.

[jieyouxu]

r? Kobzol (since you're looking at it already)

[Kobzol]

Thanks! You might want to modify the PR title and description.

@bors r+ rollup

[bors]

📌 Commit e13af7a has been approved by Kobzol

It is now in the queue for this repository.

[bors]

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.