Chore: Add tests and comments (refs #349) (#487)

lib/espree.js

@@ -171,6 +171,19 @@ export default () => Parser => {
             program.start = program.body.length ? program.body[0].start : program.start;
             program.end = extra.lastToken ? extra.lastToken.end : program.end;
 
+            /*
+             * https://github.com/eslint/espree/issues/349
+             * Ensure that template elements have correct range information.
+             * This is one location where Acorn produces a different value
+             * for its start and end properties vs. the values present in the
+             * range property. In order to avoid confusion, we set the start
+             * and end properties to the values that are present in range.
+             * This is done here, instead of in finishNode(), because Acorn
+             * uses the values of start and end internally while parsing, making
+             * it dangerous to change those values while parsing is ongoing.
+             * By waiting until the end of parsing, we can safely change these
+             * values without affect any other part of the process.
+             */
             this[STATE].templateElements.forEach(templateElement => {
                 const terminalDollarBraceL = this.input.slice(templateElement.end, templateElement.end + 2) === "${";
 
@@ -285,6 +298,7 @@ export default () => Parser => {
                     result.loc.end.column += (terminalDollarBraceL ? 2 : 1);
                 }
 
+                // save template element references to fix start/end later
                 this[STATE].templateElements.push(result);
             }
 

tests/lib/parse.js

@@ -89,6 +89,13 @@ describe("parse()", () => {
             assert.strictEqual(ast.end, ast.range[1]);
         });
 
+        it("should output the same value for program.start, end as when ranges are returned and there is a leading/trailing comments using default options", () => {
+            const ast = espree.parse("/* foo */ bar /* baz */");
+
+            assert.strictEqual(ast.start, 10);
+            assert.strictEqual(ast.end, 13);
+        });
+
         it("should output the same value for program.start, end and range and loc when there is a leading comments with range and loc true", () => {
             const ast = espree.parse("/* foo */ bar", {
                 range: true,
@@ -152,11 +159,15 @@ describe("parse()", () => {
 
             assert.strictEqual(ast.body[0].expression.quasis[0].start, ast.body[0].expression.quasis[0].loc.start.column);
             assert.strictEqual(ast.body[0].expression.quasis[0].end, ast.body[0].expression.quasis[0].loc.end.column);
+            assert.strictEqual(ast.body[0].expression.quasis[0].start, ast.body[0].expression.quasis[0].range[0]);
+            assert.strictEqual(ast.body[0].expression.quasis[0].end, ast.body[0].expression.quasis[0].range[1]);
+            assert.strictEqual(ast.body[0].expression.quasis[1].start, ast.body[0].expression.quasis[1].loc.start.column);
+            assert.strictEqual(ast.body[0].expression.quasis[1].end, ast.body[0].expression.quasis[1].loc.end.column);
             assert.strictEqual(ast.body[0].expression.quasis[1].start, ast.body[0].expression.quasis[1].range[0]);
             assert.strictEqual(ast.body[0].expression.quasis[1].end, ast.body[0].expression.quasis[1].range[1]);
         });
 
-        it("should output the same value for loc, range and start and end in templateElement", () => {
+        it("should output the same value for start and end in templateElement as when ranges are present", () => {
             const ast = espree.parse("`foo ${bar}`;", {
                 ecmaVersion: 6
             });