feat(ui): render per-element Template attributes

.agents/skills/jaws/SKILL.md

@@ -165,6 +165,13 @@ These are the two usual building blocks for widget handlers passed to `$.Button`
 - `ui.Template` is for partial templates only; full document/page templates should be rendered through `ui.Handler`.
 - A nil-interface Template `Dot` is valid and contributes no tag; a typed nil follows its
   dynamic type's comparability and expansion behavior.
+- When a Template `Dot` implements `jaws.InitialHTMLAttrHandler`, its callback supplies
+  attributes separately for each generated wrapper's initial render. It receives the
+  concrete Element, so equal Template values may render different per-Element attributes
+  without putting attribute state in the Template. An unwrapped Template has no attribute
+  target and does not invoke the callback. The callback is not invoked by
+  `Template.JawsUpdate`; use `Element.SetAttr` and `Element.RemoveAttr` for dynamic wrapper
+  changes during updates.
 - The root dot **must** be comparable at runtime and equal to itself: `ui.NewTemplate`
   returns a value, so the dot is part of the widget the container widgets use as a map key.
   A slice, map, func or NaN-bearing dot makes the widget unusable as a container child.
@@ -232,7 +239,10 @@ JaWS parses template params as:
 Implications:
 - Non-comparable handlers are not auto-tagged unless they implement `tag.TagGetter`.
 - Pass explicit tags when dirty targeting depends on them.
-- HTML attributes passed to `$.Template(...)` are applied to the generated template wrapper.
+- HTML attributes passed to `$.Template(...)` are applied to the generated template wrapper
+  before Dot attributes and take precedence when a name is duplicated.
+- Attributes returned by the Dot's `jaws.InitialHTMLAttrHandler` are appended to that
+  wrapper during its initial render.
 - Template bodies used with `$.Template(...)` must be partials, not full documents.
 - For dynamic button text, avoid passing plain static strings if the value must change after render; use getter-based values so updates reflect new state.
 

lib/ui/AI.md

@@ -70,9 +70,14 @@ available through `rw.NewUI(ui.NewX(...), params...)`.
 `rw.Template(outerTag, name, dot, params...)` renders a partial template inside
 a generated addressable JaWS wrapper. An empty outer tag selects `div`; choose a
 semantic wrapper such as `tr`, `td`, `li`, or `option` when DOM context requires
-it. Attributes passed in params apply to the wrapper. Full page templates belong
-in `ui.Handler`; static structural inclusion should use Go's native template
-action:
+it. Attributes passed in params apply to the wrapper and take precedence when
+the dot callback returns an attribute with the same name. When dot implements
+`jaws.InitialHTMLAttrHandler`, its callback supplies attributes separately for
+each wrapper's initial render; equal Template values may therefore render
+different Element-specific attributes without storing them in the Template.
+The callback is not invoked during `Template.JawsUpdate`. Full page templates
+belong in `ui.Handler`; static structural inclusion should use Go's native
+template action:
 
 ```gotemplate
 {{template "partial" .Dot}}
@@ -133,6 +138,14 @@ does not run initial-attribute hooks. Call `Element.ApplyInitialHTMLAttr`
 separately and without holding a lock that the callback might acquire. A
 `bind.Binder` acquires its own value lock before invoking its hook.
 
+A wrapped Template applies this initial-attribute hook to its Dot after claiming
+the Element state slot and resolving the named partial. The result is written
+directly to that Element's wrapper and is not retained in Template state. An
+unwrapped Template has no attribute target and does not invoke the callback.
+Wrapper attributes persist when `Template.JawsUpdate` replaces only the inner
+HTML; dynamic wrapper changes use `Element.SetAttr` and `Element.RemoveAttr`
+during update processing.
+
 Getter paths must not mutate domain state. They may queue wrapper changes with
 Element update methods so class/attribute changes flush with the HTML update.
 HTMLInner-backed widgets unconditionally queue `SetInner` when updated; input

lib/ui/template.go

@@ -23,10 +23,17 @@ import (
 // runtime and equal to itself, and Dot must be usable as a tag under
 // [tag.TagExpand].
 //
+// If Dot implements [jaws.InitialHTMLAttrHandler], its callback supplies wrapper
+// attributes separately for each wrapped Element's initial render. An unwrapped
+// Template has no attribute target and does not invoke the callback. The callback
+// is not invoked during [Template.JawsUpdate].
+//
 // OuterHTMLTag names the wrapper that receives the JaWS ID and render-time HTML
-// attributes. An empty field renders without a wrapper, making [Template.JawsUpdate]
-// a no-op. [NewTemplate] defaults an empty wrapper argument to "div". The named
-// template must be a partial; use [Handler] for a complete document.
+// attributes from render parameters and Dot. Render-parameter attributes take
+// precedence when Dot returns an attribute with the same name. An empty field
+// renders without a wrapper, making [Template.JawsUpdate] a no-op. [NewTemplate]
+// defaults an empty wrapper argument to "div". The named template must be a
+// partial; use [Handler] for a complete document.
 //
 // A Template owns the Elements created through its [RequestWriter]. A successful
 // update unregisters Elements from the previous execution. Elements created by a
@@ -41,7 +48,7 @@ import (
 type Template struct {
 	OuterHTMLTag string // Wrapper element; empty renders unwrapped and disables JawsUpdate.
 	Name         string // Template name to be looked up using Jaws.LookupTemplate.
-	Dot          any    // Template data exposed as With.Dot and expanded for tag registration.
+	Dot          any    // Template data, tag source, event delegate, and initial-attribute source.
 }
 
 var (
@@ -155,9 +162,10 @@ func writeTemplateWrapperStart(elem *jaws.Element, w io.Writer, outerHTMLTag str
 }
 
 func (tmpl Template) render(elem *jaws.Element, w io.Writer, params []any) (err error) {
-	// Claim the state slot before anything observable happens: tag registration, handler
-	// registration and every write come after, so a contended Element fails having
-	// changed nothing rather than having half-registered itself.
+	// Claim the state slot before anything observable happens: Dot expansion, tag and
+	// handler registration, template lookup, initial-attribute callbacks, and every
+	// write come after, so a contended Element fails having changed nothing rather
+	// than having half-registered itself.
 	st := &templateState{}
 	if err = jaws.SetElementState(elem, st); err != nil {
 		return
@@ -172,6 +180,11 @@ func (tmpl Template) render(elem *jaws.Element, w io.Writer, params []any) (err
 		var lookedUp *template.Template
 		if lookedUp, err = tmpl.lookup(elem); err == nil {
 			if doWrap {
+				// HTML parsing keeps the first duplicate attribute, so append Dot
+				// attributes after render-parameter attributes.
+				for _, attr := range elem.ApplyInitialHTMLAttr(tmpl.Dot) {
+					attrs = append(attrs, string(attr))
+				}
 				err = writeTemplateWrapperStart(elem, w, tmpl.OuterHTMLTag, attrs)
 			}
 			if err == nil {
@@ -283,7 +296,8 @@ func (tmpl Template) JawsInput(elem *jaws.Element, value string) (err error) {
 // dot may be a nil interface. Otherwise it must make the returned Template
 // comparable and equal to itself, and it must be usable as a tag under
 // [tag.TagExpand]. Use the returned Template as a value; taking its address is
-// unsupported.
+// unsupported. If dot implements [jaws.InitialHTMLAttrHandler], its callback
+// supplies attributes separately for each generated wrapper's initial render.
 func NewTemplate(outerHTMLTag, name string, dot any) Template {
 	if outerHTMLTag == "" {
 		outerHTMLTag = "div"
@@ -297,8 +311,11 @@ func newTemplate(outerHTMLTag, name string, dot any) Template {
 
 // Template renders the named partial template with dot exposed as [With.Dot].
 //
-// The generated outerHTMLTag wrapper owns the JaWS ID and HTML attributes in
-// params. An empty outerHTMLTag defaults to "div". See [NewTemplate].
+// The generated outerHTMLTag wrapper owns the JaWS ID, HTML attributes in params,
+// and attributes returned by dot when it implements
+// [jaws.InitialHTMLAttrHandler]. Attributes in params take precedence when dot
+// returns an attribute with the same name. An empty outerHTMLTag defaults to
+// "div". See [NewTemplate].
 func (rw RequestWriter) Template(outerHTMLTag, name string, dot any, params ...any) error {
 	return rw.NewUI(NewTemplate(outerHTMLTag, name, dot), params...)
 }

lib/ui/template_handler_test.go

@@ -27,6 +27,25 @@ type templateDot struct {
 	menus   int
 }
 
+type templateInitialAttrDot struct {
+	mu    sync.Mutex
+	calls []jaws.Jid
+}
+
+func (d *templateInitialAttrDot) JawsInitialHTMLAttr(elem *jaws.Element) template.HTMLAttr {
+	d.mu.Lock()
+	d.calls = append(d.calls, elem.Jid())
+	d.mu.Unlock()
+	return template.HTMLAttr(`data-element="` + elem.Jid().String() + `"`)
+}
+
+func (d *templateInitialAttrDot) attrCalls() (calls []jaws.Jid) {
+	d.mu.Lock()
+	calls = append(calls, d.calls...)
+	d.mu.Unlock()
+	return
+}
+
 func (d *templateDot) JawsUpdate(elem *jaws.Element) {
 	d.updated++
 }
@@ -174,6 +193,72 @@ func TestTemplate_RenderUpdateEventAndHelpers(t *testing.T) {
 	}
 }
 
+func TestNewTemplate_RendersDotInitialHTMLAttrPerElement(t *testing.T) {
+	jw, rq := newCoreRequest(t)
+	if err := jw.AddTemplateLookuper(template.Must(template.New("attrtmpl").Parse(`content`))); err != nil {
+		t.Fatal(err)
+	}
+
+	dot := new(templateInitialAttrDot)
+	first := NewTemplate("article", "attrtmpl", dot)
+	second := NewTemplate("article", "attrtmpl", dot)
+	if first != second {
+		t.Fatal("Templates rebuilt from the same definition are not equal")
+	}
+	definitions := map[Template]struct{}{first: {}}
+	if _, ok := definitions[second]; !ok {
+		t.Fatal("equal Template is not usable as a map key")
+	}
+
+	provider := &testContainer{contents: []jaws.UI{first, second}}
+	containerElem, got := renderUI(t, rq, NewContainer("section", provider))
+	children := containerElements(t, containerElem)
+	if len(children) != 2 {
+		t.Fatalf("Template children = %d, want 2", len(children))
+	}
+	if templateStateOf(children[0]) == templateStateOf(children[1]) {
+		t.Fatal("equal Templates share per-Element state")
+	}
+	for _, child := range children {
+		want := `<article id="` + child.Jid().String() + `" data-element="` + child.Jid().String() + `">content</article>`
+		if !strings.Contains(got, want) {
+			t.Errorf("rendered HTML %q does not contain %q", got, want)
+		}
+	}
+
+	calls := dot.attrCalls()
+	if len(calls) != len(children) {
+		t.Fatalf("JawsInitialHTMLAttr calls = %v, want one per Template Element", calls)
+	}
+	for i, child := range children {
+		if calls[i] != child.Jid() {
+			t.Errorf("JawsInitialHTMLAttr call %d used Element %v, want %v", i, calls[i], child.Jid())
+		}
+	}
+
+	children[0].JawsUpdate()
+	if calls = dot.attrCalls(); len(calls) != len(children) {
+		t.Fatalf("JawsInitialHTMLAttr calls after update = %v, want initial-render calls only", calls)
+	}
+}
+
+func TestTemplate_RenderCombinesParamAndDotInitialHTMLAttrs(t *testing.T) {
+	jw, rq := newCoreRequest(t)
+	if err := jw.AddTemplateLookuper(template.Must(template.New("attrtmpl").Parse(`content`))); err != nil {
+		t.Fatal(err)
+	}
+
+	dot := new(templateInitialAttrDot)
+	elem, got := renderUI(t, rq, NewTemplate("article", "attrtmpl", dot), template.HTMLAttr(`class="param"`))
+	want := `class="param" data-element="` + elem.Jid().String() + `"`
+	if !strings.Contains(got, want) {
+		t.Fatalf("rendered HTML does not contain ordered attributes %q: %q", want, got)
+	}
+	if calls := dot.attrCalls(); len(calls) != 1 || calls[0] != elem.Jid() {
+		t.Fatalf("JawsInitialHTMLAttr calls = %v, want [%v]", calls, elem.Jid())
+	}
+}
+
 func TestTemplate_RenderWithTableRowWrapper(t *testing.T) {
 	jw, rq := newCoreRequest(t)
 	// The native template action includes the structural td fragment without another
@@ -412,13 +497,43 @@ func TestTemplate_UpdateLogsMissingTemplate(t *testing.T) {
 	}
 }
 
+func TestTemplate_RenderMissingTemplateSkipsDotInitialHTMLAttr(t *testing.T) {
+	_, rq := newCoreRequest(t)
+	dot := new(templateInitialAttrDot)
+	tmpl := NewTemplate("div", "missingtemplate", dot)
+	elem := rq.NewElement(tmpl)
+
+	if err := elem.JawsRender(io.Discard, nil); !errors.Is(err, ErrMissingTemplate) {
+		t.Fatalf("render error = %v, want %v", err, ErrMissingTemplate)
+	}
+	if calls := dot.attrCalls(); len(calls) != 0 {
+		t.Fatalf("missing Template invoked JawsInitialHTMLAttr for %v", calls)
+	}
+}
+
 func TestNewTemplate_EmptyWrapperDefaultsToDiv(t *testing.T) {
 	tpl := NewTemplate("", "partial", tag.Tag("dot"))
 	if tpl.OuterHTMLTag != "div" {
 		t.Fatalf("OuterHTMLTag = %q, want %q", tpl.OuterHTMLTag, "div")
 	}
 }
 
+func TestTemplate_UnwrappedSkipsDotInitialHTMLAttr(t *testing.T) {
+	jw, rq := newCoreRequest(t)
+	if err := jw.AddTemplateLookuper(template.Must(template.New("unwrapped").Parse(`content`))); err != nil {
+		t.Fatal(err)
+	}
+
+	dot := new(templateInitialAttrDot)
+	_, got := renderUI(t, rq, Template{Name: "unwrapped", Dot: dot})
+	if got != "content" {
+		t.Fatalf("unwrapped Template rendered %q, want %q", got, "content")
+	}
+	if calls := dot.attrCalls(); len(calls) != 0 {
+		t.Fatalf("unwrapped Template invoked JawsInitialHTMLAttr for %v", calls)
+	}
+}
+
 // TestTemplate_UpdateLogsExecuteError needs a template whose initial render succeeds and
 // whose later update fails: a wrapped Template updates only an Element it rendered, so a
 // template that always fails could never establish the state slot to begin with.

lib/ui/template_state_test.go

@@ -327,8 +327,9 @@ func TestTemplate_SecondClaimRegistersNoHandler(t *testing.T) {
 
 // TestTemplate_SecondClaimOnOneElementFails covers the contention path through the
 // supported shape — one renderer delegating to two Templates — and proves the claim
-// precedes every side effect: the rejected Template writes nothing and registers no tag.
-// TestTemplate_SecondClaimRegistersNoHandler covers the handler list.
+// precedes every side effect: the rejected Template writes nothing, registers no tag
+// and invokes no initial-attribute callback. TestTemplate_SecondClaimRegistersNoHandler
+// covers the handler list.
 func TestTemplate_SecondClaimOnOneElementFails(t *testing.T) {
 	for _, tt := range []struct {
 		name   string
@@ -341,7 +342,7 @@ func TestTemplate_SecondClaimOnOneElementFails(t *testing.T) {
 			_, rq := newStateRequest(t)
 
 			firstDot := tag.Tag("first")
-			secondDot := tag.Tag("second")
+			secondDot := new(templateInitialAttrDot)
 			ui := &contendingUI{
 				first:  NewTemplate("div", "state-plain", firstDot),
 				second: NewTemplate("div", "state-b", secondDot),
@@ -368,6 +369,9 @@ func TestTemplate_SecondClaimOnOneElementFails(t *testing.T) {
 			if got := len(rq.GetElements(secondDot)); got != 0 {
 				t.Fatalf("elements tagged by the rejected Template = %d, want 0", got)
 			}
+			if calls := secondDot.attrCalls(); len(calls) != 0 {
+				t.Fatalf("rejected Template invoked JawsInitialHTMLAttr for %v", calls)
+			}
 			if got := len(rq.GetElements(tag.Tag("param"))); got != 0 {
 				t.Fatalf("elements tagged from the rejected render's params = %d, want 0", got)
 			}