Do it correctly.

DanielRosenwasser · DanielRosenwasser · commit dac00d97b742 · 2018-08-15T09:00:23.000-07:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -15473,7 +15473,7 @@ namespace ts {
                 // With noImplicitThis, functions may not reference 'this' if it has type 'any'
                 error(
                     node,
-                    capturedByArrowFunction ?
+                    capturedByArrowFunction && container.kind === SyntaxKind.SourceFile ?
                         Diagnostics.The_containing_arrow_function_captures_the_global_value_of_this_which_implicitly_has_type_any :
                         Diagnostics.this_implicitly_has_type_any_because_it_does_not_have_a_type_annotation);
             }

Original file line number	Diff line number	Diff line change
`@@ -15473,7 +15473,7 @@ namespace ts {`
`15473`	`15473`	`// With noImplicitThis, functions may not reference 'this' if it has type 'any'`
`15474`	`15474`	`error(`
`15475`	`15475`	`node,`
`15476`		`- capturedByArrowFunction ?`
	`15476`	`+ capturedByArrowFunction && container.kind === SyntaxKind.SourceFile ?`
`15477`	`15477`	`Diagnostics.The_containing_arrow_function_captures_the_global_value_of_this_which_implicitly_has_type_any :`
`15478`	`15478`	`Diagnostics.this_implicitly_has_type_any_because_it_does_not_have_a_type_annotation);`
`15479`	`15479`	`}`