WIP

Author: JamesHenry

lib/rules/restrict-plus-operands.js

@@ -0,0 +1,58 @@
+/**
+ * @fileoverview When adding two variables, operands must both be of type number or of type string.
+ * @author James Henry
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "When adding two variables, operands must both be of type number or of type string.",
+            category: "TypeScript"
+        },
+        schema: []
+    },
+
+    create: function(context) {
+
+        //----------------------------------------------------------------------
+        // Public
+        //----------------------------------------------------------------------
+        return {
+            BinaryExpression(node) {
+
+                var ts = context.parserServices.ts;
+                var tsNode = context.parserServices.getTSNode(node);
+
+                if (tsNode.operatorToken.kind === ts.SyntaxKind.PlusToken) {
+
+                    var program = context.parserServices.getCurrentProgram();
+                    var tc = program.getTypeChecker();
+                    var leftType = tc.typeToString(tc.getTypeAtLocation(tsNode.left));
+                    var rightType = tc.typeToString(tc.getTypeAtLocation(tsNode.right));
+
+                    if (leftType !== rightType) {
+                        context.report({
+                            node: node,
+                            message: "Cannot add a '" + leftType + "' to a '" + rightType + "'."
+                        });
+                        return;
+                    }
+
+                    if (leftType !== "number" && leftType !== "string") {
+                        context.report({
+                            node: node,
+                            message: "'" + leftType + "' is not a supported type for addition."
+                        });
+                        return;
+                    }
+
+                }
+            }
+        };
+    }
+};

package.json

@@ -18,10 +18,10 @@
     "requireindex": "~1.1.0"
   },
   "devDependencies": {
-    "eslint": "~3.0.0",
+    "eslint": "git+https://github.com/eslint/eslint.git#7695828dc0472e61c58298bfa3f0c07418c2edac",
     "eslint-config-eslint": "^3.0.0",
     "mocha": "^2.4.5",
-    "typescript-eslint-parser": "^0.4.0"
+    "typescript-eslint-parser": "git+https://github.com/eslint/typescript-eslint-parser.git#79983ec86a54898dd8cdaa6d037f3f30e9822b6d"
   },
   "engines": {
     "node": ">=4"

tests/lib/rules/restrict-plus-operands.js

@@ -0,0 +1,53 @@
+/**
+ * @fileoverview When adding two variables, operands must both be of type number or of type string.
+ * @author James Henry
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var rule = require("../../../lib/rules/restrict-plus-operands"),
+    RuleTester = require("eslint").RuleTester;
+
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+var ruleTester = new RuleTester();
+ruleTester.run("restrict-plus-operands", rule, {
+
+    valid: [
+        {
+            code: "var foo = 1 + 1;",
+            parser: "typescript-eslint-parser"
+        },
+        {
+            code: "var foo = '1' + '1';",
+            parser: "typescript-eslint-parser"
+        },
+    ],
+
+    invalid: [
+        {
+            code: "var foo = '1' + 1;",
+            parser: "typescript-eslint-parser",
+            errors: [{
+                message: "Cannot add a 'string' to a 'number'.",
+                line: 1,
+                column: 11
+            }]
+        },
+        {
+            code: "var foo = [] + {};",
+            parser: "typescript-eslint-parser",
+            errors: [{
+                message: "'{}' is not a supported type for addition.",
+                line: 1,
+                column: 11
+            }]
+        }
+    ]
+});