[build-tools] Load local composite function catalog at build runtime

[sswrk]

Why

This PR stack adds local composite functions for EAS workflows (uses: ./.eas/functions/...). Earlier PRs define the schema, expand calls into steps, and wire inputs/outputs. The build runtime still needs to load those function.yml files from the project and pass them into StepsConfigParser.

This PR is the I/O layer: discover referenced local composite functions on disk, validate them, and hand the catalog to the parser for custom builds and generic jobs.

How

• Adds catalog helpers in @expo/steps (buildCompositeFunctionCatalogFromStepsAsync, resolveLocalCompositeFunctionPath)
• Adds packages/build-tools/src/steps/compositeFunctions.ts to resolve paths relative to the EAS project root, read function.yml / function.yaml, and validate with CompositeFunctionConfigZ
• Wires the catalog into runCustomBuildAsync and runGenericJobAsync

Test Plan

Added unit tests for catalog loading and custom-build parse integration.

[linear-code]

ENG-22387

[sswrk]

• [eas-cli] Validate legacy command/path local functions referenced from workflows #4098
• [build-tools] Load legacy command/path local functions and resolve module paths #4097
• [steps] Expand legacy command/path local functions to a single build step #4096
• [eas-build-job] Accept legacy command/path custom function shape in function.yml #4095
• [eas-cli] Validate local composite functions referenced from workflow hooks #4064
• [build-tools] Load composite function catalogs for hook steps #4063
• [steps] Support local composite functions in hook steps #4062
• [steps] Unify the default gating of steps with no if: across steps, composite scopes, and hooks #4061
• [eas-cli] Validate local composite functions in workflow files #3931
• [build-tools] Load local composite function catalog at build runtime #3930 👈 (View in Graphite)
• [steps][4/4] Resolve composite function outputs #4015
• [steps][3/4] Interpolate composite function inputs #4014
• [steps][2/4] Expand composite function references into build steps #3929 : 1 other dependent PR (#4013 )
• [steps][1/4] Add isCompositeFunctionPath and reject local composite functions in custom builds #3956
• [eas-build-job] Add local composite function schema #3928
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.20%. Comparing base (ea32f67) to head (dee4cd3).

Files with missing lines	Patch %	Lines
...ckages/build-tools/src/steps/compositeFunctions.ts	90.00%	3 Missing ⚠️
packages/steps/src/index.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3930      +/-   ##
==========================================
+ Coverage   62.15%   62.20%   +0.05%     
==========================================
  Files         993      994       +1     
  Lines       44658    44716      +58     
  Branches     9403     9409       +6     
==========================================
+ Hits        27754    27812      +58     
- Misses      15455    15457       +2     
+ Partials     1449     1447       -2     

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[claude]

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[sjchmiela]

Is keeping filesystem io in build tools a goal for us?

[sswrk]

Not a hard goal, just me being careful about not breaking any boundaries here. We could move this to steps, which would also help with the duplication between build-tools and eas-cli #3931 (comment) if you think that is okay

[sjchmiela]

supposedly these two tests are going to fail

[sjchmiela]

Suggested change

	});
	});
	it('does not load composite functions beyond the maximum nesting depth', async () => {
	const paths = Array.from({ length: 11 }, (_, index) => `./.eas/functions/a${index}`);
	const loadCompositeFunction = jest.fn(async (compositeFunctionPath: string) => {
	const index = paths.indexOf(compositeFunctionPath);
	if (index === 10) {
	throw new Error('function beyond maximum depth was loaded');
	}
	return CompositeFunctionConfigZ.parse({
	runs: {
	steps: [{ uses: paths[index + 1] }],
	},
	});
	});
	const catalog = await buildCompositeFunctionCatalogFromStepsAsync({
	rootSteps: [{ uses: paths[0] }],
	loadCompositeFunction,
	});
	expect(loadCompositeFunction).toHaveBeenCalledTimes(10);
	expect(Object.keys(catalog)).toEqual(paths.slice(0, 10));
	});
	it('does not let an error beyond the maximum depth mask the nesting-depth error', async () => {
	const paths = Array.from({ length: 11 }, (_, index) => `./.eas/functions/a${index}`);
	const catalog = await buildCompositeFunctionCatalogFromStepsAsync({
	rootSteps: [{ uses: paths[0] }],
	loadCompositeFunction: async compositeFunctionPath => {
	const index = paths.indexOf(compositeFunctionPath);
	if (index === 10) {
	throw new Error('missing composite function beyond maximum depth');
	}
	return CompositeFunctionConfigZ.parse({
	runs: {
	steps: [{ uses: paths[index + 1] }],
	},
	});
	},
	});
	expect(Object.keys(catalog)).toEqual(paths.slice(0, 10));
	});

[sswrk]

I think it's not that bad if we let build-tools load those files that user intends to load. The depth limit is an expansion time concern and it's going to error there, so the logic stays isolated.

[github-actions]

✅ Thank you for adding the changelog entry!

[sswrk]

Merged with 2 non-blocking open discussions to no longer block this feature. There are similar/related PRs coming with hooks support, so we can follow up there.