From a91cdccfc509e0878a8b8993e10aaa3a65246673 Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Fri, 25 Mar 2016 16:37:28 -0700
Subject: [PATCH] Add --noImplicitThis flag

It's basically another --noImplicitAny error, but one that would break
large amount of JavaScript-style code.
---
 src/compiler/checker.ts                       |  4 ++
 src/compiler/commandLineParser.ts             |  4 ++
 src/compiler/diagnosticMessages.json          |  6 ++-
 src/compiler/types.ts                         |  1 +
 .../noImplicitThisFunctions.errors.txt        | 25 +++++++++++++
 .../reference/noImplicitThisFunctions.js      | 37 +++++++++++++++++++
 .../cases/compiler/noImplicitThisFunctions.ts | 19 ++++++++++
 7 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/noImplicitThisFunctions.errors.txt
 create mode 100644 tests/baselines/reference/noImplicitThisFunctions.js
 create mode 100644 tests/cases/compiler/noImplicitThisFunctions.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 51fad3e7f33..0f9287f9c52 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7707,6 +7707,10 @@ namespace ts {
                 }
             }
 
+            if (compilerOptions.noImplicitThis && isFunctionLike(container)) {
+                // With noImplicitThis, functions may not reference 'this' if it has type 'any'
+                error(node, Diagnostics.this_implicitly_has_type_any_because_it_does_not_have_a_type_annotation);
+            }
             return anyType;
         }
 
diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index cf55f030c33..363a3fdfc8f 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -125,6 +125,10 @@ namespace ts {
             type: "boolean",
             description: Diagnostics.Raise_error_on_expressions_and_declarations_with_an_implied_any_type,
         },
+        {
+            name: "noImplicitThis",
+            type: "boolean",
+        },
         {
             name: "noLib",
             type: "boolean",
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 5ea860f00af..53d0bcc07b8 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1863,7 +1863,11 @@
         "category": "Error",
         "code": 2680
     },
-    "Import declaration '{0}' is using private name '{1}'.": {
+    "'this' implicitly has type 'any' because it does not have a type annotation.": {
+        "category": "Error",
+        "code": 2681
+    },
+   "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000
     },
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 5965a39a79e..e4c376b7b25 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2395,6 +2395,7 @@ namespace ts {
         noEmitOnError?: boolean;
         noErrorTruncation?: boolean;
         noImplicitAny?: boolean;
+        noImplicitThis?: boolean;
         noLib?: boolean;
         noResolve?: boolean;
         out?: string;
diff --git a/tests/baselines/reference/noImplicitThisFunctions.errors.txt b/tests/baselines/reference/noImplicitThisFunctions.errors.txt
new file mode 100644
index 00000000000..b00949d5086
--- /dev/null
+++ b/tests/baselines/reference/noImplicitThisFunctions.errors.txt
@@ -0,0 +1,25 @@
+tests/cases/compiler/noImplicitThisFunctions.ts(14,12): error TS2681: 'this' implicitly has type 'any' because it does not have a type annotation.
+
+
+==== tests/cases/compiler/noImplicitThisFunctions.ts (1 errors) ====
+    
+    function f1(x) {
+        // implicit any is still allowed
+        return x + 1;
+    }
+    
+    function f2(y: number) {
+        // ok: no reference to this
+        return y + 1;
+    }
+    
+    function f3(z: number): number {
+        // error: this is implicitly any
+        return this.a + z;
+               ~~~~
+!!! error TS2681: 'this' implicitly has type 'any' because it does not have a type annotation.
+    }
+    
+    // ok, arrow functions don't even bind `this`, so `this` is just `window`
+    let f4: (b: number) => number = b => this.c + b;
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/noImplicitThisFunctions.js b/tests/baselines/reference/noImplicitThisFunctions.js
new file mode 100644
index 00000000000..e256df2d77f
--- /dev/null
+++ b/tests/baselines/reference/noImplicitThisFunctions.js
@@ -0,0 +1,37 @@
+//// [noImplicitThisFunctions.ts]
+
+function f1(x) {
+    // implicit any is still allowed
+    return x + 1;
+}
+
+function f2(y: number) {
+    // ok: no reference to this
+    return y + 1;
+}
+
+function f3(z: number): number {
+    // error: this is implicitly any
+    return this.a + z;
+}
+
+// ok, arrow functions don't even bind `this`, so `this` is just `window`
+let f4: (b: number) => number = b => this.c + b;
+
+
+//// [noImplicitThisFunctions.js]
+var _this = this;
+function f1(x) {
+    // implicit any is still allowed
+    return x + 1;
+}
+function f2(y) {
+    // ok: no reference to this
+    return y + 1;
+}
+function f3(z) {
+    // error: this is implicitly any
+    return this.a + z;
+}
+// ok, arrow functions don't even bind `this`, so `this` is just `window`
+var f4 = function (b) { return _this.c + b; };
diff --git a/tests/cases/compiler/noImplicitThisFunctions.ts b/tests/cases/compiler/noImplicitThisFunctions.ts
new file mode 100644
index 00000000000..1e0aa0c4da0
--- /dev/null
+++ b/tests/cases/compiler/noImplicitThisFunctions.ts
@@ -0,0 +1,19 @@
+// @noImplicitThis: true
+
+function f1(x) {
+    // implicit any is still allowed
+    return x + 1;
+}
+
+function f2(y: number) {
+    // ok: no reference to this
+    return y + 1;
+}
+
+function f3(z: number): number {
+    // error: this is implicitly any
+    return this.a + z;
+}
+
+// ok, arrow functions don't even bind `this`, so `this` is just `window`
+let f4: (b: number) => number = b => this.c + b;