Can Semantic Equality Check in Custom Types be Asymmetrical?

Terraform Providers Plugin Development
2

Hi @zliang-akamai :wave:

The link you supplied uses the following semantic equality check:

// CustomStringValue defined in the value type section
// Ensure the implementation satisfies the expected interfaces
var _ basetypes.StringValuableWithSemanticEquals = CustomStringValue{}

func (v CustomStringValue) StringSemanticEquals(ctx context.Context, newValuable basetypes.StringValuable) (bool, diag.Diagnostics) {
    var diags diag.Diagnostics

    // The framework should always pass the correct value type, but always check
    newValue, ok := newValuable.(CustomStringValue)

    if !ok {
        diags.AddError(
            "Semantic Equality Check Error",
            "An unexpected value type was received while performing semantic equality checks. "+
            "Please report this to the provider developers.\n\n"+
            "Expected Value Type: "+fmt.Sprintf("%T", v)+"\n"+
            "Got Value Type: "+fmt.Sprintf("%T", newValuable),
        )

        return false, diags
    }

    // Skipping error checking if CustomStringValue already implemented RFC3339 validation
    priorTime, _ := time.Parse(time.RFC3339, v.StringValue.ValueString())

    // Skipping error checking if CustomStringValue already implemented RFC3339 validation
    newTime, _ := time.Parse(time.RFC3339, newValue.ValueString())

    // If the times are equivalent, keep the prior value
    return priorTime.Equal(newTime), diags
}

The StringSemanticEquals method is defined on CustomStringValue which will always represent the oldValue. Because of the way in which semantic equality checks are implemented on custom types, semantic equality checking will always be oldValue.SemanticEquals(ctx, newValue).

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