bug: wrong variable in error message in compose/values_merge.go

[kuishou68]

Description

In compose/values_merge.go, the mergeValues function contains a wrong variable in the error message when checking stream reader types.

Code

ss := make([]streamReader, len(vs)-1)
for i := 0; i < len(ss); i++ {
    sri, ok_ := vs[i+1].(streamReader)
    if !ok_ {
        return nil, fmt.Errorf("(mergeStream) unexpected type. "+
            "expect: %v, got: %v", t0, reflect.TypeOf(vs[i]))  // BUG: should be vs[i+1]
    }

Bug

When the type assertion vs[i+1].(streamReader) fails, the error message shows reflect.TypeOf(vs[i]) (the previous element) instead of reflect.TypeOf(vs[i+1]) (the element that actually failed the assertion).

This causes the error message to report the wrong type, making debugging significantly harder because the user sees a type that successfully passed the assertion rather than the one that failed.

Fix

Change reflect.TypeOf(vs[i]) to reflect.TypeOf(vs[i+1]) on the error line.

return nil, fmt.Errorf("(mergeStream) unexpected type. "+
    "expect: %v, got: %v", t0, reflect.TypeOf(vs[i+1]))  // FIXED

[kuishou68]

A fix has been submitted in PR #975. The change corrects the variable from vs[i] to vs[i+1] so the error message shows the type of the element that actually failed the type assertion.