Deprecate, remove `--moduleResolution classic`

[DanielRosenwasser]

In TypeScript 7.0, we have no plans to reimplement --moduleResolution classic - its behavior does not model any resolution system in widespread use, and at best it's just an approximation that avoids Node.js style resolution. Users will be better of using nodenext or bundler if necessary.

In TypeScript 6.0, --moduleResolution classic will be deprecated. Users enabling it will get an error message that can only be suppressed via --ignoreDeprecations.

In 7.0, we are thinking the default will be bundler unless there is an appropriate moduleResolution target that matches a given --module target.

See more on deprecations/changes for 6.0/7.0 in #54500.

[DanielRosenwasser]

See also #11434, where I said we were doing this years ago. 😅

[DanielRosenwasser]

Updated the issue to mention using bundler as the default in 7.0.

[alshdavid]

its behavior does not model any resolution system in widespread use

I know not many people distribute their apps as unbundled ESM in the browser, but that is a valid resolution target used by many when sandboxing applications.

Regardless, a simple "relative paths with file extensions" resolution strategy seems sensible to continue maintaining. I know for sure that I need it

[DanielRosenwasser]

Note: this is a bit iffy since the default might still be classic, but it'll be deprecated.