d2ir: Add exception for &label filter

d2ast/d2ast.go

@@ -804,6 +804,10 @@ func (kp *KeyPath) Copy() *KeyPath {
 	return &kp2
 }
 
+func (kp *KeyPath) Last() *StringBox {
+	return kp.Path[len(kp.Path)-1]
+}
+
 func IsDoubleGlob(pattern []string) bool {
 	return len(pattern) == 3 && pattern[0] == "*" && pattern[1] == "" && pattern[2] == "*"
 }

d2ir/compile.go

@@ -414,6 +414,7 @@ func (c *compiler) compileMap(dst *Map, ast, scopeAST *d2ast.Map) {
 			}
 		}
 	}
+
 	for _, n := range ast.Nodes {
 		switch {
 		case n.MapKey != nil:
@@ -554,8 +555,31 @@ func (c *compiler) ampersandFilter(refctx *RefContext) bool {
 		return false
 	}
 	if len(fa) == 0 {
+		if refctx.Key.Key.Last().ScalarString() != "label" {
 			return false
 		}
+		kp := refctx.Key.Key.Copy()
+		kp.Path = kp.Path[:len(kp.Path)-1]
+		if len(kp.Path) == 0 {
+			fa = append(fa, ParentField(refctx.ScopeMap))
+		} else {
+			fa, err = refctx.ScopeMap.EnsureField(kp, refctx, false, c)
+			if err != nil {
+				c.err.Errors = append(c.err.Errors, err.(d2ast.Error))
+				return false
+			}
+		}
+		for _, f := range fa {
+			label := f.Name
+			if f.Primary_ != nil {
+				label = f.Primary_.Value.ScalarString()
+			}
+			if label != refctx.Key.Value.ScalarBox().Unbox().ScalarString() {
+				return false
+			}
+		}
+		return true
+	}
 	for _, f := range fa {
 		ok := c._ampersandFilter(f, refctx)
 		if !ok {

d2ir/filter_test.go

@@ -96,6 +96,31 @@ x -> y
 				assertQuery(t, m, 0, 0, nil, "(x -> y)[1]")
 			},
 		},
+		{
+			name: "id-filter",
+			run: func(t testing.TB) {
+				m, err := compile(t, `
+x
+y
+p: p
+
+*.style.opacity: 0.1
+*: {
+  &label: x
+  style.opacity: 1
+}
+*: {
+  &label: p
+  style.opacity: 0.5
+}
+`)
+				assert.Success(t, err)
+				assertQuery(t, m, 9, 0, nil, "")
+				assertQuery(t, m, 0, 0, 1, "x.style.opacity")
+				assertQuery(t, m, 0, 0, 0.1, "y.style.opacity")
+				assertQuery(t, m, 0, 0, 0.5, "p.style.opacity")
+			},
+		},
 	}
 
 	runa(t, tca)