Add ConfigKit comparison acquisition

integrations/ckconfig/configkit_adapter.go

@@ -11,7 +11,7 @@ import (
 	configkit "gitea.maximumdirect.net/eric/ConfigKit"
 )
 
-// FromConfigKit adapts a typed ConfigKit loader to all four native
+// FromConfigKit adapts a typed ConfigKit loader to all five native
 // configuration operations. The loader receives the operation's explicit
 // Selection, initialized input, and shared invocation state, and runs only when
 // an installed operation selects this scope. Construction and help do not call
@@ -24,7 +24,7 @@ func FromConfigKit[I, S, T any](
 	scope := Scope[I, S]{
 		Name:       name,
 		Summary:    summary,
-		Operations: []Operation{Validate, Show, Sources, Explain},
+		Operations: []Operation{Validate, Show, Sources, Explain, Diff},
 	}
 	if load == nil {
 		return WithScopeError(scope, fmt.Errorf("ConfigKit scope %q loader must not be nil", name))
@@ -49,10 +49,71 @@ func FromConfigKit[I, S, T any](
 			Diagnostics: configKitDiagnostics(name, sources, result.Diagnostics()),
 		}, nil
 	}
+	scope.Compare = func(ctx context.Context, request ComparisonRequest[I], state S) (commandkit.Acquired[[]configkit.Difference], error) {
+		if err := ctx.Err(); err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{}, fmt.Errorf("ConfigKit scope %q comparison before left load: %w", name, err)
+		}
+
+		left, leftDiagnostics, err := loadComparisonSide(ctx, name, "left", load, request.Left, state)
+		diagnostics := append([]commandkit.Diagnostic(nil), leftDiagnostics...)
+		if err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{Diagnostics: diagnostics}, err
+		}
+
+		if err := ctx.Err(); err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{Diagnostics: diagnostics}, fmt.Errorf("ConfigKit scope %q comparison after left load: %w", name, err)
+		}
+
+		right, rightDiagnostics, err := loadComparisonSide(ctx, name, "right", load, request.Right, state)
+		diagnostics = append(diagnostics, rightDiagnostics...)
+		if err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{Diagnostics: diagnostics}, err
+		}
+
+		if err := ctx.Err(); err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{Diagnostics: diagnostics}, fmt.Errorf("ConfigKit scope %q comparison before native diff: %w", name, err)
+		}
+
+		differences, err := configkit.Diff(left, right)
+		if err != nil {
+			return commandkit.Acquired[[]configkit.Difference]{Diagnostics: diagnostics}, fmt.Errorf("ConfigKit scope %q native diff: %w", name, err)
+		}
+		return commandkit.Acquired[[]configkit.Difference]{Value: differences, Diagnostics: diagnostics}, nil
+	}
 	return scope
 }
 
+func loadComparisonSide[I, S, T any](
+	ctx context.Context,
+	scope, side string,
+	load func(context.Context, Selection, I, S) (*configkit.Result[T], error),
+	request ComparisonSide[I],
+	state S,
+) (*configkit.Result[T], []commandkit.Diagnostic, error) {
+	result, err := load(ctx, request.Selection, request.Input, state)
+	if err != nil {
+		var loadError *configkit.LoadError
+		var diagnostics []commandkit.Diagnostic
+		if errors.As(err, &loadError) && loadError != nil {
+			diagnostics = configKitComparisonDiagnostics(scope, side, loadError.Sources(), loadError.Diagnostics())
+		}
+		return nil, diagnostics, fmt.Errorf("ConfigKit scope %q %s load: %w", scope, side, err)
+	}
+	if result == nil {
+		return nil, nil, fmt.Errorf("ConfigKit scope %q %s loader returned a nil result", scope, side)
+	}
+	return result, configKitComparisonDiagnostics(scope, side, result.Sources(), result.Diagnostics()), nil
+}
+
 func configKitDiagnostics(scope string, sources []configkit.SourceInfo, records []configkit.Diagnostic) []commandkit.Diagnostic {
+	return configKitDiagnosticsWithHeading("Configuration scope "+strconv.Quote(scope)+":\n", sources, records)
+}
+
+func configKitComparisonDiagnostics(scope, side string, sources []configkit.SourceInfo, records []configkit.Diagnostic) []commandkit.Diagnostic {
+	return configKitDiagnosticsWithHeading("Configuration scope "+strconv.Quote(scope)+" "+side+":\n", sources, records)
+}
+
+func configKitDiagnosticsWithHeading(heading string, sources []configkit.SourceInfo, records []configkit.Diagnostic) []commandkit.Diagnostic {
 	if len(records) == 0 {
 		return nil
 	}
@@ -72,7 +133,7 @@ func configKitDiagnostics(scope string, sources []configkit.SourceInfo, records
 	return []commandkit.Diagnostic{{
 		Severity: severity,
 		Write: func(writer io.Writer) error {
-			if err := writeDiagnosticText(writer, "Configuration scope "+strconv.Quote(scope)+":\n"); err != nil {
+			if err := writeDiagnosticText(writer, heading); err != nil {
 				return err
 			}
 			if len(sources) > 0 {