Google feedback on TS 6.0-beta

[cecilyhunt]

Acknowledgement

• I acknowledge that issues using this template may be closed without further explanation at the maintainer's discretion.

Comment

This GitHub issue contains feedback on the TS 6.0-beta release from the team
that is responsible for keeping Google's internal software working with the
latest version of TypeScript.

Executive summary

• We do not expect to have significant difficulty in upgrading Google to TS
  6.0.
• Some changes to our TypeScript code are required to fix compilation.
  • Most of the new errors are clearly related to announced changes.
  • Detail sections below explain the changes we expect to make to unblock
    the upgrade.
• We expect some deprecations to cause difficulty upgrading to TS 7.0.
  • We plan to provide feedback about this at a later date.

Impact summary

Change description	Announced	Libraries affected
strict defaults to true	Yes	~0.1%
Legacy module syntax for namespaces deprecated	Yes	~0.02%

The Announced column indicates whether we were able to connect the observed
change with a section in the TS6.0-beta announcement.

The following sections give more detailed explanations of the changes listed
above.

Announced changes for TS 6.0

strict now defaults to true

We support this change.

We will set strict to false until we clean up newly revealed errors in our
codebase. We have not previously enabled strictBuiltinIteratorReturn and
alwaysStrict.

lib.d.ts changes

We support these changes.

As part of this migration, for impacted .d.ts files, we will update
conflicting typings where necessary. For impacted .ts files, we will add
// @ts-ignore suppressions to silence pre-existing errors with a note advising
code authors to revisit the code and fix these genuine problems.

module syntax for namespaces is deprecated

We support this change.

We will update usages of module that declare namespaces to namespace.

"ignoreDeprecations": "6.0"

We will set this in order to roll out TS 6.0 as soon as possible. We plan to
provide additional feedback about the impact of these deprecations on TS 7.0 at
a later date.

Deprecations affecting TS 7.0

The following deprecations do not affect our adoption of TS 6.0 but will need to
be addressed before we adopt TS 7.0.

es5 and --downlevelIteration deprecation

We currently use ES5 output for a small number of legacy development purposes
and are exploring using another transpiler to continue producing it in the
future.

--baseUrl deprecation

We have resolved this issue by prepending the previous baseUrl value to our
path mapping.

--esModuleInterop false and --allowSyntheticDefaultImports false deprecations

We have code patterns that rely on setting these options to true and will be
evaluating how to proceed.

Other changes

We support the following changes but have nothing else to add:

• es2025 option for target and lib
• New types for Temporal
• New types for "upsert" methods
• Regexp.escape

The following changes are largely irrelevant in our codebase and we don't have
anything to add about them:

• Subpath imports starting with #/
• Combining --moduleResolution bundler with --module commonjs
• rootDir now defaults to .
• types now defaults to []
• Other default changes
• Other deprecations

Unannounced changes

We were not able to associate any new breakages with specific unannounced
changes. If we find any, we will update this.

[DanielRosenwasser]

Thanks @cecilyhunt! Just to clarify when you said

We do not expect to have significant difficulty in upgrading Google to TS 6.0

would you still find it difficult even without the option of turning on ignoreDeprecations? 😅

I figure it's worth asking because we want to make sure these aren't just challenges for a 7.0 migration.