gum-tool-import-from-gumx

name	gum-tool-import-from-gumx
description	The "Import from .gumx" dialog. Triggers: ImportFromGumxPlugin, GumxDependencyResolver, ImportTreeNodeViewModel, ImportFromGumxView, importing components/screens/behaviors/standards across projects, the dialog's TreeView templating.

Import from .gumx Dialog

Cross-project import dialog (Content → Import → ".gumx…"). Lets the user pick a source .gumx (local or URL), preview its Components/Screens/Behaviors/Standards in a checkbox TreeView, and import a selected subset into the currently open project.

Layout (one-screen map)

• Gum/ImportFromGumxPlugin/MainImportFromGumxPlugin.cs — plugin entry, menu item, DI wiring.
• Tools/Gum.Presentation/Plugins/ImportPlugin/Services/GumxSourceService — loads source .gumx (file path or URL).
• Tools/Gum.Presentation/ImportFromGumx/Services/GumxDependencyResolver — ComputeTransitive(...) → DependencySet { TransitiveComponents, Behaviors, DifferingStandards, DifferingStandardDiffs }. Standards that differ from destination are included; standards that match are excluded entirely. The DifferingStandardDiffs dictionary (#2779) carries the full StandardComparisonResult per differing standard so the dialog can render a variable-level diff.
• Tools/Gum.Presentation/ImportFromGumx/Services/GumxImportService — performs the actual import + conflict reporting.

All three concrete services above (and their interfaces) live in the headless Gum.Presentation assembly (no WPF) — their dependency closures were already headless, so the concrete classes moved too, not just their interfaces. GumxSourceService/IGumxSourceService keep their original Gum.Plugins.ImportPlugin.Services namespace; GumxDependencyResolver/GumxImportService use ImportFromGumxPlugin.Services.

• ViewModels/ImportFromGumxViewModel — orchestrates load/preview/import; owns RootNodes and RecomputeTransitiveDependencies().
• Tools/Gum.ProjectServices/ImportFromGumx/ImportTreeNodeViewModel — one node in the TreeView; folder or leaf; carries IsChecked, InclusionState, optional StandardDiffRows. Lives in the headless net8.0 Gum.ProjectServices assembly (no WPF) so its display logic is unit-testable without standing up WPF (#3229, ADR-0003/0004); namespace stays ImportFromGumxPlugin.ViewModels.
• Tools/Gum.ProjectServices/ImportFromGumx/StandardDiffRowViewModel — passive Kind + Summary display record for one diff entry (same headless assembly; sibling ImportPreviewItemViewModel.cs holds the ElementItemType/InclusionState enums).
• Views/ImportFromGumxView.xaml + .xaml.cs — the dialog.
• ViewModels/StandardDiffDetailsViewModel.cs + Views/StandardDiffDetailsView.xaml — the read-only "Details..." modal launched from a flagged Standard row.

InclusionState bookkeeping (#2642)

Three sets of state live on ImportFromGumxViewModel:

• _autoAddedComponentNames — components that the resolver pulled in transitively. Cleared and rebuilt every recompute pass. Auto-added items get reset to NotIncluded first so unchecked-by-user deselection sticks.
• _userExplicitBehaviorNames / _userExplicitStandardNames — behaviors/standards the user explicitly checked. Must be preserved across recompute, because RecomputeTransitiveDependencies wipes those groups and rebuilds from resolver output.

When you touch the recompute loop: always detach OnItemPropertyChanged before mutating InclusionState, then re-attach. Otherwise the mutation re-enters the recompute path and clobbers tracking.

TreeView templating

One HierarchicalDataTemplate per row: a horizontal StackPanel with the checkbox and an optional "Details..." Hyperlink next to it. The hyperlink's Visibility is bound to ImportTreeNodeViewModel.IsDetailsButtonVisible (a bool [DependsOn(nameof(StandardDiffRows))] computed property) through a stock BooleanToVisibilityConverter, so it only shows on flagged-Standard rows. The hyperlink's Command reaches up to ImportFromGumxViewModel.ShowStandardDiffCommand via RelativeSource AncestorType={x:Type UserControl}, with the row VM passed as CommandParameter. Clicking opens StandardDiffDetailsView (a separate DialogService modal) which renders the row's StandardDiffRows.

A Hyperlink (inside a TextBlock) rather than a Button because a padded Button overflows the TreeViewItem row height and causes consecutive rows to visually overlap.

Why no inline expander

Early attempts embedded an Expander directly in the TreeView row to show the diff in-place. That fought several layers at once:

1. HierarchicalDataTemplate.ItemTemplateSelector is a plain CLR property, not a DependencyProperty — DynamicResource is illegal there (XamlParseException at load); StaticResource works but creates a chicken-and-egg with templates that reference the selector.
2. TreeView.ItemTemplateSelector only fires at the root level — nested rows (children of folder nodes) fall back to the default template unless every HierarchicalDataTemplate also sets its own selector. No auto-cascade.
3. The Frb theme defines a HeaderTemplate on Expander that treats Header content as data (binds {Binding} and renders via ToString). A raw CheckBox in <Expander.Header> renders as System.Windows.Controls.CheckBox Content:Foo IsChecked:True, not as a control.

Each had a workaround, but stacking them in the same row produced a brittle XAML/theme arrangement. The "Details..." button + separate modal trades one extra click for zero theme conflicts and ~30 lines of XAML.

Diff row generation

ImportFromGumxViewModel.BuildDiffRows(StandardComparisonResult) flattens:

• Added/removed categories → StandardDiffRowViewModel("Category added"|"Category removed", name).
• Each StandardVariableDiff → one row with Kind mapped from StandardVariableDiffKind (Added/Removed/Changed) and Summary = "{Variable} · {Field}: {Default} → {Project} · ...".

Returns null when there are no rows so the selector falls through to the default template and no expander is drawn.

Testing

• ImportFromGumxViewModelTests (in GumToolUnitTests) uses InitializeFromProjectForTesting(GumProjectSave) to bypass the file/URL load and seed the source. The _projectState field exposes the destination (a FakeProjectState whose GumProjectSave is mutable) so tests can stage destination standards/components for diff and conflict scenarios.
• GumxDependencyResolverTests operate on the resolver directly without going through the VM.
• ImportTreeNodeViewModelTests lives in Tests/Gum.ProjectServices.Tests (net8.0, no WPF stood up) — it covers the node's IsChecked folder/child cascade and the IsDetailsButtonVisible flag. That the node VM is testable without WPF is the payoff of moving it into the headless assembly (#3229).

History notes

• #2642 fixed user-explicit behaviors/standards being wiped on the dispatcher tick.
• #2644 added the conflict-resolution dialog (Skip / Overwrite All).
• #2779 added variable-level diff rendering for flagged Standards. The underlying diff infrastructure (IStandardComparer in Tools/Gum.ProjectServices) already existed for the CLI; this issue surfaces it in the UI.