feat(patterns): helper for interface guard inheritance

[erights]

Closes: #XXXX
Refs: https://hackmd.io/@rekmarks/H1X6VtP5eg#

Description

https://hackmd.io/@rekmarks/H1X6VtP5eg# @rekmarks explains the need to express that one interface guard effectively extends another. In a slack thread, @michaelfig explains how all we need is a helper that can extract the method guards from an super/base interface guard which can then be used with ... when defining a sub/derived interface guard. Revising the name to fit this PR, @michaelfig 's pattern is

const I2 = M.interface('I2', {
  ...getNamedMethodGuards(I1),
  doMore: M.call().returns(M.any()),
});

By putting the ... first, the sub/derived interface guard can override "inherited" interface guards as well as adding new ones.

Note that this ignores symbol-named method guards. This feature is deprecated anyway, and will hopefully disappear soon. (TODO links to PRs that will make symbol-named methods and method guards disappear.)

Security Considerations

By making it easier to express interface guards, programmers are more likely to use non-vacuous interface guards, i.e., with method guards. Without explicit method guards or patterns, our experience is that ad-hoc input validation is hard. Interface guards with method guards with patterns expresses the type-like portion of interface validation in a declarative, readable, reviewable, and sound manner. The remaining input validation burden on the manually written "raw" exo methods then is more like it would be in a soundly-statically-typed ocap language. In our before/after experience, this is typically much smaller and more reliably reviewable.

Thus, this change is good for security.

Scaling Considerations

none

Documentation Considerations

@michaelfig 's inheritance pattern is nice and should be explained somewhere. Where?

Testing Considerations

Tested in @endo/exo by exo-wobbly-point.test.js since that's already about class inheritance, which naturally goes with interface inheritance.

Compatibility Considerations

It ignores symbol-named methods. This is unlikely to cause any problems now, and will help prevent new problems when we withdraw that "feature".

By internally using getInterfaceGuardPayload, we remain tolerant of the old deprecated klass-based interface-guard representation. Unfortunately, this compat is still needed by agoric-sdk.

Upgrade Considerations

none. Unless I'm missing something?

[Copilot]

Pull Request Overview

This PR introduces a helper function getNamedMethodGuards to support interface guard inheritance patterns. The function enables developers to extend one interface guard from another using JavaScript's spread operator.

• Adds getNamedMethodGuards function that extracts string-named method guards from an interface guard
• Updates comment formatting for consistency with JSDoc standards
• Fixes default guard assignment logic in exo-tools.js

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/patterns/src/patterns/getGuardPayloads.js	Adds the new getNamedMethodGuards helper function and improves comment formatting
packages/exo/src/exo-tools.js	Fixes default guard assignment to use undefined instead of the uninitialized variable

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[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

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[erights]

Ready for review

[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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[rekmarks]

LGTM!