feat: omitting default attribute on get is now out.global

src/__tests__/fixture.ts

@@ -92,7 +92,7 @@ export default (
               expect: chai.expect,
               ...helpers,
               fireEvent,
-              ...(await helpers.render(template, input)),
+              ...(await helpers.render(template, { ...input })),
             } as FixtureHelpers;
 
             await snapshot("html", fixtureHelpers.container);

src/__tests__/fixtures/get-and-set/__snapshots__/error-get-args/node.compile.error.expected.txt

@@ -1,4 +1,4 @@
-src/__tests__/fixtures/get-and-set/templates/error-get-args.marko(2,4): The <get> tag 'default' attribute is required.
+src/__tests__/fixtures/get-and-set/templates/error-get-args.marko(2,4): The <get> tag requires a tag variable.
   1 | <set=1>
 > 2 |   <get(y)/x="."/>
     |    ^^^

src/__tests__/fixtures/get-and-set/__snapshots__/error-get-args/web.compile.error.expected.txt

@@ -1,4 +1,4 @@
-src/__tests__/fixtures/get-and-set/templates/error-get-args.marko(2,4): The <get> tag 'default' attribute is required.
+src/__tests__/fixtures/get-and-set/templates/error-get-args.marko(2,4): The <get> tag requires a tag variable.
   1 | <set=1>
 > 2 |   <get(y)/x="."/>
     |    ^^^

src/__tests__/fixtures/get-and-set/__snapshots__/get-global-context/node.render.expected.html

@@ -0,0 +1,3 @@
+<div>
+  hello
+</div>

src/__tests__/fixtures/get-and-set/__snapshots__/get-global-context/web.render.expected.html

@@ -0,0 +1,3 @@
+<div>
+  hello
+</div>

src/__tests__/fixtures/get-and-set/__snapshots__/get-mutate-global-context/node.compile.error.expected.txt

@@ -0,0 +1,7 @@
+src/__tests__/fixtures/get-and-set/templates/error-assign-global-context.marko(3,3): Cannot mutate the global context.
+  1 | <get/{ message }/>
+  2 | <button onClick() {
+> 3 |   message = "World";
+    |   ^^^^^^^^^^^^^^^^^
+  4 | }>${message}</button>
+  5 |

src/__tests__/fixtures/get-and-set/__snapshots__/get-mutate-global-context/web.compile.error.expected.txt

@@ -0,0 +1,7 @@
+src/__tests__/fixtures/get-and-set/templates/error-assign-global-context.marko(3,3): Cannot mutate the global context.
+  1 | <get/{ message }/>
+  2 | <button onClick() {
+> 3 |   message = "World";
+    |   ^^^^^^^^^^^^^^^^^
+  4 | }>${message}</button>
+  5 |

src/__tests__/fixtures/get-and-set/index.test.ts

@@ -93,6 +93,13 @@ describe(
   fixture("./templates/provide-across-children/index.marko")
 );
 
+describe(
+  "<get> global context",
+  fixture("./templates/get-global-context.marko", {
+    $global: { message: "hello" },
+  })
+);
+
 describe("error <get> args", fixture("./templates/error-get-args.marko"));
 
 describe(
@@ -111,13 +118,13 @@ describe(
 );
 
 describe(
-  "error <get> missing tag",
-  fixture("./templates/error-get-missing-tag.marko")
+  "<get> mutate global context",
+  fixture("./templates/error-assign-global-context.marko")
 );
 
 describe(
-  "error <get> no default attr",
-  fixture("./templates/error-get-no-default-attr.marko")
+  "error <get> missing tag",
+  fixture("./templates/error-get-missing-tag.marko")
 );
 
 describe(

src/__tests__/fixtures/get-and-set/templates/error-assign-global-context.marko

@@ -0,0 +1,4 @@
+<get/{ message }/>
+<button onClick() {
+  message = "World";
+}>${message}</button>

src/__tests__/fixtures/get-and-set/templates/get-global-context.marko

@@ -0,0 +1,2 @@
+<get/{ message }/>
+<div>${message}</div>

src/components/get/transform.ts

@@ -6,24 +6,46 @@ import getAttr from "../../util/get-attr";
 export = function transform(tag: t.NodePath<t.MarkoTag>) {
   const file = tag.hub.file;
   const defaultAttr = getAttr(tag, "default")!;
-  const errorMessage = !defaultAttr
-    ? "'default' attribute is required"
-    : tag.node.attributes.length > 1
-    ? "only supports the 'default' attribute"
-    : !tag.node.var
-    ? "requires a tag variable"
-    : tag.node.arguments
-    ? "does not support arguments"
-    : tag.node.body.params.length
-    ? "does not support tag body parameters"
-    : tag.node.body.body.length
-    ? "does not support body content"
-    : undefined;
+  const errorMessage =
+    defaultAttr && tag.node.attributes.length > 1
+      ? "only supports the 'default' attribute"
+      : !tag.node.var
+      ? "requires a tag variable"
+      : tag.node.arguments
+      ? "does not support arguments"
+      : tag.node.body.params.length
+      ? "does not support tag body parameters"
+      : tag.node.body.body.length
+      ? "does not support body content"
+      : undefined;
 
   if (errorMessage) {
     throw tag.get("name").buildCodeFrameError(`The <get> tag ${errorMessage}.`);
   }
 
+  if (!defaultAttr) {
+    for (const name in tag.get("var").getBindingIdentifiers()) {
+      for (const violation of tag.scope.getOwnBinding(name)!
+        .constantViolations) {
+        throw violation.buildCodeFrameError(
+          "Cannot mutate the global context."
+        );
+      }
+    }
+
+    tag.replaceWith(
+      t.markoScriptlet([
+        t.variableDeclaration("const", [
+          t.variableDeclarator(
+            tag.node.var!,
+            t.memberExpression(t.identifier("out"), t.identifier("global"))
+          ),
+        ]),
+      ])
+    );
+    return;
+  }
+
   let fromValue = defaultAttr.node.value;
 
   if (t.isStringLiteral(fromValue)) {