Minor improvements to block-scoping/tdz (#6782)

* Add test case for simple reference in tdz

* Add more examples from old issues as test cases

* Fix two testcases by excluding function declarations from being tdz checked

* Document the  option for block-scoping

* Add test cases with destructuring assignments

* Remove failing test cases

* [skip ci] Include type and default value for options

packages/babel-plugin-transform-block-scoping/README.md

@@ -70,7 +70,10 @@ require("@babel/core").transform("code", {
 });
 ```
 
-## Options `throwIfClosureRequired`
+## Options
+
+### `throwIfClosureRequired`
+`boolean`, defaults to `false`.
 
 In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:
 
@@ -81,3 +84,15 @@ for (let i = 0; i < 5; i++) {
 ```
 
 In extremely performance-sensitive code, this can be undesirable. If `"throwIfClosureRequired": true` is set, Babel throws when transforming these patterns instead of automatically adding an additional function.
+
+### `tdz`
+`boolean`, defaults to `false`.
+
+By default this plugin will ignore the *temporal dead zone (TDZ)* for block-scoped variables. The following code will **not throw an error when transpiled with Babel, which is not spec compliant**:
+
+```javascript
+i
+let i;
+```
+
+If you need these errors you can tell Babel to try and find them by setting `"tdz": true` for this plugin. However, the current implementation might not get all edge cases right and its best to just avoid code like this in the first place.

packages/babel-plugin-transform-block-scoping/src/tdz.js

@@ -38,6 +38,8 @@ export const visitor = {
 
     const bindingPath = scope.getBinding(node.name).path;
 
+    if (bindingPath.isFunctionDeclaration()) return;
+
     const status = getTDZStatus(path, bindingPath);
     if (status === "inside") return;
 

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/block-ref-function-call/exec.js

@@ -0,0 +1,3 @@
+f();
+
+const f = function f() {}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/block-ref-function-call/options.json

@@ -0,0 +1,3 @@
+{
+	"throws": "f is not defined - temporal dead zone"
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/destructured-self-reference/exec.js

@@ -0,0 +1 @@
+let { b: d } = { d }

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/destructured-self-reference/options.json

@@ -0,0 +1,3 @@
+{
+	"throws": "d is not defined - temporal dead zone"
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/function-call-no-throw/exec.js

@@ -0,0 +1,5 @@
+function f() {
+    x;
+}
+let x;
+f();

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/hoisted-function/exec.js

@@ -0,0 +1,3 @@
+f();
+
+function f() {}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/hoisted-var/exec.js

@@ -0,0 +1,3 @@
+x = 3;
+
+var x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/options.json

@@ -0,0 +1,3 @@
+{
+	"plugins": [["transform-block-scoping",{"tdz": true}]]
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/self-reference/exec.js

@@ -0,0 +1 @@
+let x = x;

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/self-reference/options.json

@@ -0,0 +1,3 @@
+{
+	"throws": "x is not defined - temporal dead zone"
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/shadow-outer-var/exec.js

@@ -0,0 +1,3 @@
+var a = 5;
+if (a){ console.log(a); let a = 2; }
+console.log(a);

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/shadow-outer-var/options.json

@@ -0,0 +1,3 @@
+{
+	"throws": "a is not defined - temporal dead zone"
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/simple-reference/exec.js

@@ -0,0 +1,2 @@
+i
+let i

packages/babel-plugin-transform-block-scoping/test/fixtures/tdz/simple-reference/options.json

@@ -0,0 +1,3 @@
+{
+	"throws": "i is not defined - temporal dead zone"
+}