[kian99]

The Juju errors package introduced a generic AsType function before it was introduced in Go 1.26. Our implementation didn't cater for multiple wrapped errors e.g. the following test fails,

func TestAsTypeMultipleWrappedErrors(t *testing.T) {
    target := &fs.PathError{Op: "open", Path: "/missing", Err: fs.ErrNotExist}
    err := fmt.Errorf("%w: %w", io.EOF, target)

    got, ok := errors.AsType[*fs.PathError](err)
    if !ok || got != target {
        t.Fatalf("AsType() = (%v, %v), want (%v, true)", got, ok, target)
    }
}

This change updates the go.mod to 1.26 and switches to the stdlib AsType implementation.

Note: I'm not sure which branch this should land in v1/v2/master. Juju currently uses the v1 branch so I've opted for that but master is a few commits ahead.

[Copilot]

🟡 Changes recommended

The replacement tests need a multiple-wrapped-error regression case to protect the intended fix.

1 open issue

• Add test coverage for multiple wrapped errors · New

What changed in this PR

This PR delegates Juju’s generic AsType helper to the Go standard library to support error trees containing multiple wrapped errors.

Changes:

• Raises the minimum Go version from 1.18 to 1.26.
• Replaces custom AsType traversal with stderrors.AsType.
• Replaces the previous generic-helper tests with Juju wrapper cases.

File	Description
go.mod	Requires Go 1.26 for standard-library AsType.
functions.go	Delegates AsType to the standard library and simplifies its documentation.
functions_test.go	Replaces existing AsType and HasType coverage with wrapper-focused tests.

_{Review effort: Balanced}