fix arrowhead label detection

ci/release/changelogs/next.md

@@ -9,3 +9,4 @@
 #### Bugfixes ⛑️
 
 - Fixes `d2` erroring on malformed user paths (`fdopendir` error). [util-go#10](https://github.com/terrastruct/util-go/pull/10)
+- Arrowhead labels being set without maps wasn't being picked up. [#1015](https://github.com/terrastruct/d2/pull/1015)

d2compiler/compile.go

@@ -488,9 +488,7 @@ func (c *compiler) compileEdgeField(edge *d2graph.Edge, f *d2ir.Field) {
 	}
 
 	if f.Name == "source-arrowhead" || f.Name == "target-arrowhead" {
-		if f.Map() != nil {
-			c.compileArrowheads(edge, f)
-		}
+		c.compileArrowheads(edge, f)
 	}
 }
 
@@ -508,21 +506,23 @@ func (c *compiler) compileArrowheads(edge *d2graph.Edge, f *d2ir.Field) {
 		c.compileLabel(attrs, f)
 	}
 
-	for _, f2 := range f.Map().Fields {
-		keyword := strings.ToLower(f2.Name)
-		_, isReserved := d2graph.SimpleReservedKeywords[keyword]
-		if isReserved {
-			c.compileReserved(attrs, f2)
-			continue
-		} else if f2.Name == "style" {
-			if f2.Map() == nil {
+	if f.Map() != nil {
+		for _, f2 := range f.Map().Fields {
+			keyword := strings.ToLower(f2.Name)
+			_, isReserved := d2graph.SimpleReservedKeywords[keyword]
+			if isReserved {
+				c.compileReserved(attrs, f2)
+				continue
+			} else if f2.Name == "style" {
+				if f2.Map() == nil {
+					continue
+				}
+				c.compileStyle(attrs, f2.Map())
+				continue
+			} else {
+				c.errorf(f2.LastRef().AST(), `source-arrowhead/target-arrowhead map keys must be reserved keywords`)
 				continue
 			}
-			c.compileStyle(attrs, f2.Map())
-			continue
-		} else {
-			c.errorf(f2.LastRef().AST(), `source-arrowhead/target-arrowhead map keys must be reserved keywords`)
-			continue
 		}
 	}
 }

d2compiler/compile_test.go

@@ -971,6 +971,17 @@ x -> y: {
 				}
 			},
 		},
+		{
+			name: "edge_arrowhead_primary",
+
+			text: `x -> y: {
+  source-arrowhead: Reisner's Rule of Conceptual Inertia
+}
+`,
+			assertions: func(t *testing.T, g *d2graph.Graph) {
+				assert.String(t, "Reisner's Rule of Conceptual Inertia", g.Edges[0].SrcArrowhead.Label.Value)
+			},
+		},
 		{
 			name: "edge_arrowhead_fields",