module: fix column offsets in errors

Because Node modules are wrapped, errors on the first line
of a file leak the wrapper to the user and report the wrong
column number. This commit adds a line break to the module
wrapper so that the first line is treated the same as all
other lines. To compensate for the additional line, a line
offset of -1 is also applied to errors.

Fixes: https://github.com/nodejs/node/issues/2860
PR-URL: https://github.com/nodejs/node/pull/2867
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/vm.markdown

@@ -26,10 +26,16 @@ The options when creating a script are:
 
 - `filename`: allows you to control the filename that shows up in any stack
   traces produced from this script.
+- `lineOffset`: allows you to add an offset to the line number that is
+  displayed in stack traces
+- `columnOffset`: allows you to add an offset to the column number that is
+  displayed in stack traces
 - `displayErrors`: whether or not to print any errors to stderr, with the
   line of code that caused them highlighted, before throwing an exception.
   Applies only to syntax errors compiling the code; errors while running the
   code are controlled by the options to the script's methods.
+- `timeout`: a number of milliseconds to execute `code` before terminating
+  execution. If execution is terminated, an `Error` will be thrown.
 
 ### script.runInContext(contextifiedSandbox[, options])
 
@@ -124,8 +130,14 @@ multiple times:
 
 The options for running a script are:
 
-- `displayErrors`: whether or not to print any runtime errors to stderr, with
+- `filename`: allows you to control the filename that shows up in any stack
-  the line of code that caused them highlighted, before throwing an exception.
+  traces produced.
+- `lineOffset`: allows you to add an offset to the line number that is
+  displayed in stack traces
+- `columnOffset`: allows you to add an offset to the column number that is
+  displayed in stack traces
+- `displayErrors`: whether or not to print any errors to stderr, with the
+  line of code that caused them highlighted, before throwing an exception.
   Applies only to runtime errors executing the code; it is impossible to create
   a `Script` instance with syntax errors, as the constructor will throw.
 - `timeout`: a number of milliseconds to execute the script before terminating
@@ -252,6 +264,10 @@ e.g. `(0,eval)('code')`. However, it also has the following additional options:
 
 - `filename`: allows you to control the filename that shows up in any stack
   traces produced.
+- `lineOffset`: allows you to add an offset to the line number that is
+  displayed in stack traces
+- `columnOffset`: allows you to add an offset to the column number that is
+  displayed in stack traces
 - `displayErrors`: whether or not to print any errors to stderr, with the
   line of code that caused them highlighted, before throwing an exception.
   Will capture both syntax errors from compiling `code` and runtime errors

lib/module.js

@@ -47,7 +47,6 @@ Module.wrapper = NativeModule.wrapper;
 Module.wrap = NativeModule.wrap;
 Module._debug = util.debuglog('module');
 
-
 // We use this alias for the preprocessor that filters it out
 const debug = Module._debug;
 
@@ -401,7 +400,8 @@ Module.prototype._compile = function(content, filename) {
   // create wrapper function
   var wrapper = Module.wrap(content);
 
-  var compiledWrapper = runInThisContext(wrapper, { filename: filename });
+  var compiledWrapper = runInThisContext(wrapper,
+                                      { filename: filename, lineOffset: -1 });
   if (global.v8debug) {
     if (!resolvedArgv) {
       // we enter the repl if we're not given a filename argument.

src/node.js

@@ -955,7 +955,7 @@
   };
 
   NativeModule.wrapper = [
-    '(function (exports, require, module, __filename, __dirname) { ',
+    '(function (exports, require, module, __filename, __dirname) {\n',
     '\n});'
   ];
 

src/node_contextify.cc

@@ -504,13 +504,15 @@ class ContextifyScript : public BaseObject {
     TryCatch try_catch;
     Local<String> code = args[0]->ToString(env->isolate());
     Local<String> filename = GetFilenameArg(args, 1);
+    Local<Integer> lineOffset = GetLineOffsetArg(args, 1);
+    Local<Integer> columnOffset = GetColumnOffsetArg(args, 1);
     bool display_errors = GetDisplayErrorsArg(args, 1);
     if (try_catch.HasCaught()) {
       try_catch.ReThrow();
       return;
     }
 
-    ScriptOrigin origin(filename);
+    ScriptOrigin origin(filename, lineOffset, columnOffset);
     ScriptCompiler::Source source(code, origin);
     Local<UnboundScript> v8_script =
         ScriptCompiler::CompileUnbound(env->isolate(), &source);
@@ -675,6 +677,39 @@ class ContextifyScript : public BaseObject {
   }
 
 
+  static Local<Integer> GetLineOffsetArg(
+                                      const FunctionCallbackInfo<Value>& args,
+                                      const int i) {
+    Local<Integer> defaultLineOffset = Integer::New(args.GetIsolate(), 0);
+
+    if (!args[i]->IsObject()) {
+      return defaultLineOffset;
+    }
+
+    Local<String> key = FIXED_ONE_BYTE_STRING(args.GetIsolate(), "lineOffset");
+    Local<Value> value = args[i].As<Object>()->Get(key);
+
+    return value->IsUndefined() ? defaultLineOffset : value->ToInteger();
+  }
+
+
+  static Local<Integer> GetColumnOffsetArg(
+                                      const FunctionCallbackInfo<Value>& args,
+                                      const int i) {
+    Local<Integer> defaultColumnOffset = Integer::New(args.GetIsolate(), 0);
+
+    if (!args[i]->IsObject()) {
+      return defaultColumnOffset;
+    }
+
+    Local<String> key = FIXED_ONE_BYTE_STRING(args.GetIsolate(),
+                                              "columnOffset");
+    Local<Value> value = args[i].As<Object>()->Get(key);
+
+    return value->IsUndefined() ? defaultColumnOffset : value->ToInteger();
+  }
+
+
   static bool EvalMachine(Environment* env,
                           const int64_t timeout,
                           const bool display_errors,

test/fixtures/test-error-first-line-offset.js

@@ -0,0 +1 @@
+error

test/parallel/test-vm-context.js

@@ -60,3 +60,15 @@ var ctx = {};
 Object.defineProperty(ctx, 'b', { configurable: false });
 ctx = vm.createContext(ctx);
 assert.equal(script.runInContext(ctx), false);
+
+// Error on the first line of a module should
+// have the correct line and column number
+assert.throws(function() {
+  vm.runInContext('throw new Error()', context, {
+    filename: 'expected-filename.js',
+    lineOffset: 32,
+    columnOffset: 123
+  });
+}, function(err) {
+  return /expected-filename.js:33:130/.test(err.stack);
+}, 'Expected appearance of proper offset in Error stack');

test/sequential/test-module-loading.js

@@ -279,3 +279,11 @@ process.on('exit', function() {
 // #1440 Loading files with a byte order marker.
 assert.equal(42, require('../fixtures/utf8-bom.js'));
 assert.equal(42, require('../fixtures/utf8-bom.json'));
+
+// Error on the first line of a module should
+// have the correct line and column number
+assert.throws(function() {
+  require('../fixtures/test-error-first-line-offset.js');
+}, function(err) {
+  return /test-error-first-line-offset.js:1:1/.test(err.stack);
+}, 'Expected appearance of proper offset in Error stack');