Handle numeric signs in 'isNumericName'.

To be fair, I don't think humanity knew about negative numbers until like 200 B.C.E.

src/compiler/checker.ts

@@ -4097,9 +4097,15 @@ module ts {
             numericScanner = numericScanner || createScanner(compilerOptions.target || ScriptTarget.ES5, /*skipTrivia*/ false);
             numericScanner.setText(name);
 
-            // Ensure that the name is nothing more than a numeric literal
-            // (i.e. it is preceded by nothing (whitespace) and scanning leaves us at the very end of the string).
-            return numericScanner.scan() === SyntaxKind.NumericLiteral && numericScanner.getTextPos() === name.length;
+            // Ensure that the name is nothing more than an optional sign (+/-) and a numeric literal
+            // (i.e. it is preceded by nothing and scanning leaves us at the very end of the string).
+            var token = numericScanner.scan();
+            
+            if (token === SyntaxKind.MinusToken || token === SyntaxKind.PlusToken) {
+                token = numericScanner.scan();
+            }
+            
+            return token === SyntaxKind.NumericLiteral && numericScanner.getTextPos() === name.length;
         }
 
         function checkObjectLiteral(node: ObjectLiteral, contextualMapper?: TypeMapper): Type {

tests/baselines/reference/propertiesAndIndexersForNumericNames.errors.txt

@@ -0,0 +1,29 @@
+tests/cases/compiler/propertiesAndIndexersForNumericNames.ts(3,3): error TS2412: Property '"1"' of type 'string' is not assignable to numeric index type 'number'.
+tests/cases/compiler/propertiesAndIndexersForNumericNames.ts(4,3): error TS2412: Property '"-1"' of type 'string' is not assignable to numeric index type 'number'.
+tests/cases/compiler/propertiesAndIndexersForNumericNames.ts(5,3): error TS2412: Property '"+1"' of type 'string' is not assignable to numeric index type 'number'.
+
+
+==== tests/cases/compiler/propertiesAndIndexersForNumericNames.ts (3 errors) ====
+    class C {
+      [i: number]: number;
+      public "1": string = "number"; // Error
+      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2412: Property '"1"' of type 'string' is not assignable to numeric index type 'number'.
+      public "-1": string = "negative number"; // Error
+      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2412: Property '"-1"' of type 'string' is not assignable to numeric index type 'number'.
+      public "+1": string = "positive number (for the paranoid)"; // Error
+      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2412: Property '"+1"' of type 'string' is not assignable to numeric index type 'number'.
+      
+      public " 1": string = "leading space"; // No error
+      public "1    ": string = "trailing space"; // No error
+      public "": string = "no nothing"; // No error
+      public "    ": string = "just space"; // No error
+      public "1 0 1": string = "several numbers and spaces"; // No error
+      public "NaN": string = "not a number"; // No error
+      public "-NaN": string = "not a negative number"; // No error
+      public "+Infinity": string = "A gillion"; // No error
+      public "-Infinity": string = "Negative-a-gillion"; // No error
+    }
+    

tests/baselines/reference/propertiesAndIndexersForNumericNames.js

@@ -0,0 +1,37 @@
+//// [propertiesAndIndexersForNumericNames.ts]
+class C {
+  [i: number]: number;
+  public "1": string = "number"; // Error
+  public "-1": string = "negative number"; // Error
+  public "+1": string = "positive number (for the paranoid)"; // Error
+  
+  public " 1": string = "leading space"; // No error
+  public "1    ": string = "trailing space"; // No error
+  public "": string = "no nothing"; // No error
+  public "    ": string = "just space"; // No error
+  public "1 0 1": string = "several numbers and spaces"; // No error
+  public "NaN": string = "not a number"; // No error
+  public "-NaN": string = "not a negative number"; // No error
+  public "+Infinity": string = "A gillion"; // No error
+  public "-Infinity": string = "Negative-a-gillion"; // No error
+}
+
+
+//// [propertiesAndIndexersForNumericNames.js]
+var C = (function () {
+    function C() {
+        this["1"] = "number"; // Error
+        this["-1"] = "negative number"; // Error
+        this["+1"] = "positive number (for the paranoid)"; // Error
+        this[" 1"] = "leading space"; // No error
+        this["1    "] = "trailing space"; // No error
+        this[""] = "no nothing"; // No error
+        this["    "] = "just space"; // No error
+        this["1 0 1"] = "several numbers and spaces"; // No error
+        this["NaN"] = "not a number"; // No error
+        this["-NaN"] = "not a negative number"; // No error
+        this["+Infinity"] = "A gillion"; // No error
+        this["-Infinity"] = "Negative-a-gillion"; // No error
+    }
+    return C;
+})();

tests/cases/compiler/propertiesAndIndexersForNumericNames.ts

@@ -0,0 +1,16 @@
+class C {
+  [i: number]: number;
+  public "1": string = "number"; // Error
+  public "-1": string = "negative number"; // Error
+  public "+1": string = "positive number (for the paranoid)"; // Error
+  
+  public " 1": string = "leading space"; // No error
+  public "1    ": string = "trailing space"; // No error
+  public "": string = "no nothing"; // No error
+  public "    ": string = "just space"; // No error
+  public "1 0 1": string = "several numbers and spaces"; // No error
+  public "NaN": string = "not a number"; // No error
+  public "-NaN": string = "not a negative number"; // No error
+  public "+Infinity": string = "A gillion"; // No error
+  public "-Infinity": string = "Negative-a-gillion"; // No error
+}