Spec compatibility for template literals. (#5791)

* Spec compatibility for template literals.

* Update preset-es2015 `spec` expected case.

* Prevent array mutability by replacing `shift`.

* Fix condition for single item.

* Group concats to ensure toPrimitive sequence.

* Update function test case.

* Add semi for function test case.

* Simplify concat call expressions creating.

* Fix some cases with multiple idengifiers.

* Add test case with different literals.

* Add test case for `Symbol()` and toPrimitive order

* Add actual literal case.

* Add minNodeVersion to template literals order.

* Flip the logical expression.

* Update README for template literals spec option.

* docs [skip ci]

packages/babel-plugin-transform-es2015-template-literals/README.md

@@ -75,16 +75,16 @@ In loose mode, tagged template literal objects aren't frozen.
 
 `boolean`, defaults to `false`.
 
-This option wraps all template literal expressions with `String`. See [babel/babel#1065](https://github.com/babel/babel/issues/1065) for more info.
+This option combines all template literal expressions and quasis with `String.prototype.concat`. It will handle cases with `Symbol.toPrimitive` correctly and throw correctly if template literal expression is a `Symbol()`. See [babel/babel#5791](https://github.com/babel/babel/pull/5791).
 
 **In**
 
 ```javascript
-`foo${bar}`;
+`foo${bar}baz${quux}${1}`;
 ```
 
 **Out**
 
 ```javascript
-"foo" + String(bar);
+"foo".concat(bar, "baz").concat(quux, 1);
 ```

packages/babel-plugin-transform-es2015-template-literals/src/index.js

@@ -1,7 +1,29 @@
 export default function ({ types: t }) {
+
+  function buildConcatCallExressions(items) {
+    let avail = true;
+    return items.reduce(function(left, right) {
+      let canBeInserted = t.isLiteral(right);
+
+      if (!canBeInserted && avail) {
+        canBeInserted = true;
+        avail = false;
+      }
+      if (canBeInserted && t.isCallExpression(left)) {
+        left.arguments.push(right);
+        return left;
+      }
+      return t.callExpression(
+        t.memberExpression(left, t.identifier("concat")),
+        [right]
+      );
+    });
+  }
+
   return {
     visitor: {
       TaggedTemplateExpression(path, state) {
+
         const { node } = path;
         const { quasi } = node;
 
@@ -45,9 +67,7 @@ export default function ({ types: t }) {
           if (index < expressions.length) {
             const expr = expressions[index++];
             const node = expr.node;
-            if (state.opts.spec && !expr.isBaseType("string") && !expr.isBaseType("number")) {
-              nodes.push(t.callExpression(t.identifier("String"), [node]));
-            } else if (!t.isStringLiteral(node, { value: "" })) {
+            if (!t.isStringLiteral(node, { value: "" })) {
               nodes.push(node);
             }
           }
@@ -55,13 +75,20 @@ export default function ({ types: t }) {
 
         // since `+` is left-to-right associative
         // ensure the first node is a string if first/second isn't
-        if (!t.isStringLiteral(nodes[0]) && !t.isStringLiteral(nodes[1])) {
+        const considerSecondNode = state.opts.spec || !t.isStringLiteral(nodes[1]);
+        if (!t.isStringLiteral(nodes[0]) && considerSecondNode) {
           nodes.unshift(t.stringLiteral(""));
         }
-
         let root = nodes[0];
-        for (let i = 1; i < nodes.length; i++) {
-          root = t.binaryExpression("+", root, nodes[i]);
+
+        if (state.opts.spec) {
+          if (nodes.length > 1) {
+            root = buildConcatCallExressions(nodes);
+          }
+        } else {
+          for (let i = 1; i < nodes.length; i++) {
+            root = t.binaryExpression("+", root, nodes[i]);
+          }
         }
 
         path.replaceWith(root);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/escape-quotes/expected.js

@@ -1 +1 @@
-var t = "'" + String(foo) + "' \"" + String(bar) + "\"";
+var t = "'".concat(foo, "' \"").concat(bar, "\"");

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/functions/expected.js

@@ -1 +1 @@
-var foo = "test " + String(_.test(foo)) + " " + String(bar);
+var foo = "test ".concat(_.test(foo), " ").concat(bar);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/literals/actual.js

@@ -0,0 +1 @@
+var foo = `${1}${f}oo${true}${b}ar${0}${baz}`;

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/literals/expected.js

@@ -0,0 +1 @@
+var foo = "".concat(1, f, "oo", true).concat(b, "ar", 0).concat(baz);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/multiple/expected.js

@@ -1 +1 @@
-var foo = "test " + String(foo) + " " + String(bar);
+var foo = "test ".concat(foo, " ").concat(bar);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/only/expected.js

@@ -1 +1 @@
-var foo = "" + String(test);
+var foo = "".concat(test);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/order/exec.js

@@ -0,0 +1,24 @@
+const calls = [];
+
+`
+  ${
+    calls.push(1),
+    {
+      [Symbol.toPrimitive](){
+        calls.push(2);
+        return 'foo';
+      }
+    }
+  }
+  ${
+    calls.push(3),
+    {
+      [Symbol.toPrimitive](){
+        calls.push(4);
+        return 'bar';
+      }
+    }
+  }
+`;
+
+assert.deepEqual(calls, [1, 2, 3, 4]);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/order/options.json

@@ -0,0 +1,3 @@
+{
+  "minNodeVersion": "6.0.0"
+}

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/single/expected.js

@@ -1 +1 @@
-var foo = "test " + String(foo);
+var foo = "test ".concat(foo);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/statement/expected.js

@@ -1 +1 @@
-var foo = "test " + String(foo + bar);
+var foo = "test ".concat(foo + bar);

packages/babel-plugin-transform-es2015-template-literals/test/fixtures/spec/symbol/exec.js

@@ -0,0 +1,3 @@
+const fn = () => `${Symbol()}`;
+
+assert.throws(fn, TypeError);

packages/babel-preset-es2015/test/fixtures/preset-options/spec/expected.js

@@ -1,7 +1,7 @@
 "use strict";
 
 var _this = undefined;
-"1" + String(a);
+"1".concat(a);
 
 (function () {
   babelHelpers.newArrowCheck(this, _this);