Lazy-install sourceMapSupport (#6651)

* Install sourceMapSupport only when sourceMaps are requested

* Add tests for sourceMapSupport

* Fix sourceMap position for tests

* Fix gen_error file

* fix the test descriptions

* Refactor install sourceMap support

* Run sourceMapSupport only once

* Handle cases where sourceMaps is undefined

packages/babel-register/src/node.js

@@ -12,21 +12,23 @@ const maps = {};
 const transformOpts = {};
 let piratesRevert = null;
 
-sourceMapSupport.install({
-  handleUncaughtExceptions: false,
-  environment: "node",
-  retrieveSourceMap(source) {
-    const map = maps && maps[source];
-    if (map) {
-      return {
-        url: null,
-        map: map,
-      };
-    } else {
-      return null;
-    }
-  },
-});
+function installSourceMapSupport() {
+  sourceMapSupport.install({
+    handleUncaughtExceptions: false,
+    environment: "node",
+    retrieveSourceMap(source) {
+      const map = maps && maps[source];
+      if (map) {
+        return {
+          url: null,
+          map: map,
+        };
+      } else {
+        return null;
+      }
+    },
+  });
+}
 
 registerCache.load();
 let cache = registerCache.get();
@@ -67,7 +69,7 @@ function compile(code, filename) {
       // Do not process config files since has already been done with the OptionManager
       // calls above and would introduce duplicates.
       babelrc: false,
-      sourceMaps: "both",
+      sourceMaps: opts.sourceMaps === undefined ? "both" : opts.sourceMaps,
       ast: false,
     }),
   );
@@ -77,7 +79,12 @@ function compile(code, filename) {
     result.mtime = mtime(filename);
   }
 
-  maps[filename] = result.map;
+  if (result.map) {
+    if (Object.keys(maps).length === 0) {
+      installSourceMapSupport();
+    }
+    maps[filename] = result.map;
+  }
 
   return result.code;
 }

packages/babel-register/test/__data__/gen_error.js

@@ -0,0 +1,4 @@
+/* eslint-disable */
+module.exports = () => { 'use strict'; let error; try { const impossible_result = ''.toFixed(); } catch (e) { error = e; } return error.stack.toString().replace('\n', ''); }
+
+

packages/babel-register/test/index.js

@@ -1,6 +1,8 @@
+import sourceMapSupport from "source-map-support";
 import chai from "chai";
 
 const DATA_ES2015 = require.resolve("./__data__/es2015");
+const GEN_ERROR = require.resolve("./__data__/gen_error");
 
 describe("@babel/register", function() {
   let babelRegister;
@@ -38,6 +40,9 @@ describe("@babel/register", function() {
     const js = require("default-require-extensions/js");
     oldCompiler = require.extensions[".js"];
     require.extensions[".js"] = js;
+    sourceMapSupport.install({
+      emptyCacheBetweenOperations: true,
+    });
   });
 
   after(() => {
@@ -47,6 +52,7 @@ describe("@babel/register", function() {
   afterEach(() => {
     revertRegister();
     delete require.cache[DATA_ES2015];
+    delete require.cache[GEN_ERROR];
   });
 
   it("registers correctly", () => {
@@ -69,4 +75,32 @@ describe("@babel/register", function() {
       })
       .to.throw(SyntaxError);
   });
+
+  it("does not install source map support if asked not to", () => {
+    setupRegister({
+      sourceMaps: false,
+    });
+
+    let gen_error;
+    chai.expect((gen_error = require(GEN_ERROR))).to.be.ok;
+    chai.expect(gen_error()).to.match(/gen_error\.js:8:34/);
+  });
+
+  it("installs source map support by default", () => {
+    setupRegister();
+
+    let gen_error;
+    chai.expect((gen_error = require(GEN_ERROR))).to.be.ok;
+    chai.expect(gen_error()).to.match(/gen_error\.js:2:86/);
+  });
+
+  it("installs source map support when requested", () => {
+    setupRegister({
+      sourceMaps: "both",
+    });
+
+    let gen_error;
+    chai.expect((gen_error = require(GEN_ERROR))).to.be.ok;
+    chai.expect(gen_error()).to.match(/gen_error\.js:2:86/);
+  });
 });