Mark ThisExpression and Super as Purish (#12251)

* Mark `ThisExpression` as `Purish`

The other purish types are functions and literals, so I
guess it means "it doesn't have side effects"

* Super & tests

* Fix tests

packages/babel-traverse/test/scope.js

@@ -232,6 +232,19 @@ describe("scope", () => {
       expect(
         getPath("String.raw`foo`").get("body")[0].get("expression").isPure(),
       ).toBeTruthy();
+      expect(getPath("this").get("body.0.expression").isPure()).toBeTruthy();
+      expect(getPath("this.foo").get("body.0.expression").isPure()).toBeFalsy();
+      expect(
+        getPath("({ m() { super.foo } })")
+          .get("body.0.expression.properties.0.body.body.0.expression")
+          .isPure(),
+      ).toBeFalsy();
+      expect(
+        // This only tests "super", not "super.foo"
+        getPath("({ m() { super.foo } })")
+          .get("body.0.expression.properties.0.body.body.0.expression.object")
+          .isPure(),
+      ).toBeTruthy();
     });
 
     test("label", function () {

packages/babel-types/src/definitions/core.js

@@ -980,7 +980,7 @@ defineType("SwitchStatement", {
 });
 
 defineType("ThisExpression", {
-  aliases: ["Expression"],
+  aliases: ["Expression", "Pureish"],
 });
 
 defineType("ThrowStatement", {
@@ -1785,7 +1785,7 @@ defineType("SpreadElement", {
 });
 
 defineType("Super", {
-  aliases: ["Expression"],
+  aliases: ["Expression", "Pureish"],
 });
 
 defineType("TaggedTemplateExpression", {

packages/babel-types/src/validators/generated/index.js

@@ -3965,7 +3965,9 @@ export function isPureish(node: ?Object, opts?: Object): boolean {
     "NullLiteral" === nodeType ||
     "BooleanLiteral" === nodeType ||
     "RegExpLiteral" === nodeType ||
+    "ThisExpression" === nodeType ||
     "ArrowFunctionExpression" === nodeType ||
+    "Super" === nodeType ||
     "BigIntLiteral" === nodeType ||
     "DecimalLiteral" === nodeType ||
     (nodeType === "Placeholder" && "StringLiteral" === node.expectedNode)