dagger/dagger · error

expected %s to be a function, got %T

Error message

expected %s to be a function, got %T

What it means

Defensive assertion in fillObjectFunctionCases: the stored constructor's type is not a *types.Signature. Should be unreachable since constructors are validated as functions earlier; indicates internal parse-state inconsistency.

Source

Thrown at cmd/codegen/generator/go/templates/modules.go:562

	}

	// Sort methods alphabetically to ensure deterministic codegen output
	sort.Slice(methods, func(i, j int) bool {
		return methods[i].fn.Name() < methods[j].fn.Name()
	})

	for _, method := range methods {
		fnName, sig := method.fn.Name(), method.fn.Type().(*types.Signature)
		if err := ps.fillObjectFunctionCase(objName, fnName, fnName, sig, method.paramSpecs, cases); err != nil {
			return err
		}
	}

	// main module object constructor case
	if hasConstructor {
		sig, ok := ps.constructor.Type().(*types.Signature)
		if !ok {
			return fmt.Errorf("expected %s to be a function, got %T", constructorFuncName, ps.constructor.Type())
		}
		paramSpecs, err := ps.parseParamSpecs(nil, ps.constructor)
		if err != nil {
			return fmt.Errorf("failed to parse %s function: %w", constructorFuncName, err)
		}

		// Validate the constructor returns the main module object (further general validation happens in fillObjectFunctionCase)
		results := sig.Results()
		if results.Len() == 0 {
			return fmt.Errorf("%s must return a value", constructorFuncName)
		}
		resultType := results.At(0).Type()
		if ptrType, ok := resultType.(*types.Pointer); ok {
			resultType = ptrType.Elem()
		}
		resultType = dealias(resultType)
		namedType, ok := resultType.(*types.Named)
		if !ok {

View on GitHub (pinned to 82ba2681db)

Solutions

1. Check the module's constructor (New) is declared as a plain function
2. Report if the constructor is valid — likely a codegen bug

When it happens

Trigger: Thrown at cmd/codegen/generator/go/templates/modules.go:562 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/a08f6c1f258abc1b. Report an issue: GitHub.