globs: fix ampersand outside glob

ci/release/changelogs/next.md

@@ -31,3 +31,4 @@
 - Fixes a panic with a connection to a grid cell that is a container in TALA [#1729](https://github.com/terrastruct/d2/pull/1729)
 - Fixes incorrect grid cell positioning when the grid has a shape set and fixes content sometimes escaping circle shapes. [#1734](https://github.com/terrastruct/d2/pull/1734)
 - Fixes content sometimes escaping cloud shapes. [#1736](https://github.com/terrastruct/d2/pull/1736)
+- Fixes panic using a glob filter (e.g. `&a`) outside globs. [#1748](https://github.com/terrastruct/d2/pull/1748)

d2ir/compile.go

@@ -394,6 +394,9 @@ func (c *compiler) ampersandFilterMap(dst *Map, ast, scopeAST *d2ast.Map) bool {
 				ScopeAST: scopeAST,
 			})
 			if !ok {
+				if len(c.mapRefContextStack) == 0 {
+					return false
+				}
 				// Unapply glob if appropriate.
 				gctx := c.getGlobContext(c.mapRefContextStack[len(c.mapRefContextStack)-1])
 				if gctx == nil {

d2ir/filter_test.go

@@ -233,6 +233,18 @@ classes: {
 TestCompile/filters/errors/bad-syntax.d2:9:1: unexpected map termination character } in file map`)
 				},
 			},
+			{
+				name: "outside-glob",
+				run: func(t testing.TB) {
+					_, err := compile(t, `jacob.style: {
+	fill: red
+	multiple: true
+}
+&a
+`)
+					assert.ErrorString(t, err, `TestCompile/filters/errors/outside-glob.d2:5:1: glob filters cannot be used outside globs`)
+				},
+			},
 			{
 				name: "no-glob",
 				run: func(t testing.TB) {