fix import underscore links

d2compiler/compile_test.go

@@ -2351,6 +2351,36 @@ layers: {
 				tassert.Equal(t, "root.layers.x", g.Layers[0].Layers[0].Objects[1].Link.Value)
 			},
 		},
+		{
+			name: "link-file-underscore",
+			text: `...@x`,
+			files: map[string]string{
+				"x.d2": `x
+
+layers: {
+  a: { c }
+  b: { d.link: _.layers.a }
+	e: {
+    l
+
+		layers: {
+			j: {
+			  k.link: _
+			  n.link: _._
+			  m.link: _._.layers.a
+			}
+		}
+  }
+}
+`,
+			},
+			assertions: func(t *testing.T, g *d2graph.Graph) {
+				tassert.Equal(t, "root.layers.a", g.Layers[1].Objects[0].Link.Value)
+				tassert.Equal(t, "root.layers.e", g.Layers[2].Layers[0].Objects[0].Link.Value)
+				tassert.Equal(t, "root", g.Layers[2].Layers[0].Objects[1].Link.Value)
+				tassert.Equal(t, "root.layers.a", g.Layers[2].Layers[0].Objects[2].Link.Value)
+			},
+		},
 		{
 			name: "link-board-underscore-not-found",
 			text: `x

d2ir/compile.go

@@ -512,7 +512,7 @@ func (c *compiler) compileMap(dst *Map, ast, scopeAST *d2ast.Map) {
 			}
 
 			OverlayMap(dst, impn.Map())
-			c.updateLinks(dst)
+			c.extendLinks(dst, ParentField(dst))
 
 			if impnf, ok := impn.(*Field); ok {
 				if impnf.Primary_ != nil {
@@ -843,6 +843,32 @@ func (c *compiler) ignoreLazyGlob(n Node) bool {
 	return false
 }
 
+// When importing a file, all of its board links need to be extended to reflect their new path
+func (c *compiler) extendLinks(m *Map, importF *Field) {
+	for _, f := range m.Fields {
+		if f.Name == "link" {
+			val := f.Primary().Value.ScalarString()
+			link, err := d2parser.ParseKey(val)
+			if err != nil {
+				continue
+			}
+			linkIDA := link.IDA()
+			if len(linkIDA) == 0 {
+				continue
+			}
+
+			importIDA := IDA(importF)
+			extendedIDA := append(importIDA, linkIDA[1:]...)
+			kp := d2ast.MakeKeyPath(extendedIDA)
+			s := d2format.Format(kp)
+			f.Primary_.Value = d2ast.MakeValueBox(d2ast.FlatUnquotedString(s)).ScalarBox().Unbox()
+		}
+		if f.Map() != nil {
+			c.extendLinks(f.Map(), importF)
+		}
+	}
+}
+
 func (c *compiler) updateLinks(m *Map) {
 	for _, f := range m.Fields {
 		if f.Name == "link" {
@@ -864,22 +890,8 @@ func (c *compiler) updateLinks(m *Map) {
 			bida := BoardIDA(f)
 			aida := IDA(f)
 
-			uplevels := -1
-			// The id path from that board to field
-			if len(aida)-len(bida) > len(bida)+1 {
-				relaida := aida[len(bida)+1 : len(aida)-len(bida)]
-				// If the link value has underscores, the path length can be less than the path length of the field
-				uplevels = len(relaida) - len(linkIDA) + 1
-			}
-
 			if len(bida) != len(aida) {
 				prependIDA := aida[:len(aida)-len(bida)]
-				if uplevels > 0 {
-					prependIDA = prependIDA[:len(prependIDA)-uplevels]
-				} else if uplevels == 0 {
-					// It's a sibling, so we go up one level to find it
-					prependIDA = prependIDA[:len(prependIDA)-2]
-				}
 				fullIDA := []string{"root"}
 				// With nested imports, a value may already have been updated with part of the absolute path
 				// E.g.,