Update: Add "safe" mode to strict (fixes #3306)

docs/rules/strict.md

@@ -26,11 +26,12 @@ This rule is aimed at using strict directives effectively, and as such, will fla
 
 ### Options
 
-There are three options for this rule:
+There are four options for this rule:
 
 1. `never` - don't use `"use strict"` at all
 1. `global` - require `"use strict"` in the global scope
 1. `function` - require `"use strict"` in function scopes only
+1. `safe` - require `"use strict"` globally when inside a module wrapper and in function scopes everywhere else.
 
 ### "never" mode
 
@@ -163,6 +164,10 @@ function foo() {
 foo();
 ```
 
+### "safe" mode
+
+Node.js and the CommonJS module system wrap modules inside a hidden function wrapper that defines each module's scope. The wrapper makes it safe to concatenate strict-mode modules while maintaining their original `"use strict"` directives. When the `node` or `commonjs` environments are enabled or `globalReturn` is enabled in `ecmaFeatures`, ESLint considers code to be inside the module wrapper, and `"safe"` mode corresponds to `"global"` mode and enforces global `"use strict"` directives. Everywhere else, `"safe"` mode corresponds to `"function"` mode and enforces `"use strict"` directives inside top-level functions.
+
 ### deprecated mode (Removed)
 
 **Replacement notice**: This mode, previously enabled by turning on the rule without specifying a mode, has been removed in ESLint v1.0. `"function"` mode is most similar to the deprecated behavior, and has been made the default if no mode is specified.

lib/rules/strict.js

@@ -57,6 +57,12 @@ module.exports = function(context) {
 
     var mode = context.options[0];
 
+    if (mode === "safe") {
+        mode = context.parserOptions.ecmaFeatures &&
+            context.parserOptions.ecmaFeatures.globalReturn ?
+            "global" : "function";
+    }
+
     /**
      * Report a node or array of nodes with a given message.
      * @param {(ASTNode|ASTNode[])} nodes Node or nodes to report.
@@ -219,6 +225,6 @@ module.exports = function(context) {
 
 module.exports.schema = [
     {
-        "enum": ["never", "global", "function"]
+        "enum": ["never", "global", "function", "safe"]
     }
 ];

tests/lib/rules/strict.js

@@ -66,7 +66,11 @@ ruleTester.run("strict", rule, {
         },
 
         // defaults to "function" mode
-        { code: "function foo() { 'use strict'; return; }" }
+        { code: "function foo() { 'use strict'; return; }" },
+
+        // "safe" mode corresponds to "global" if ecmaFeatures.globalReturn is true, otherwise "function"
+        { code: "function foo() { 'use strict'; return; }", options: ["safe"] },
+        { code: "'use strict'; function foo() { return; }", parserOptions: { ecmaFeatures: { globalReturn: true } }, options: ["safe"] }
 
     ],
     invalid: [
@@ -302,6 +306,25 @@ ruleTester.run("strict", rule, {
         }, {
             code: "function foo() { return; }",
             errors: [{ message: "Use the function form of \"use strict\".", type: "FunctionDeclaration" }]
+        },
+
+        // "safe" mode corresponds to "global" if ecmaFeatures.globalReturn is true, otherwise "function"
+        {
+            code: "'use strict'; function foo() { return; }",
+            options: ["safe"],
+            errors: [
+                { message: "Use the function form of \"use strict\".", type: "ExpressionStatement" },
+                { message: "Use the function form of \"use strict\".", type: "FunctionDeclaration" }
+            ]
+        },
+        {
+            code: "function foo() { 'use strict'; return; }",
+            parserOptions: { ecmaFeatures: { globalReturn: true } },
+            options: ["safe"],
+            errors: [
+                { message: "Use the global form of \"use strict\".", type: "Program" },
+                { message: "Use the global form of \"use strict\".", type: "ExpressionStatement" }
+            ]
         }
 
     ]