Add rule: strict-string-expressions

src/configs/all.ts

@@ -150,6 +150,7 @@ export const rules = {
     "restrict-plus-operands": true,
     "static-this": true,
     "strict-boolean-expressions": true,
+    "strict-string-expressions": true,
     "strict-comparisons": true,
     "strict-type-predicates": true,
     "switch-default": true,

src/rules/strictStringExpressionsRule.ts

@@ -0,0 +1,93 @@
+/**
+ * @license
+ * Copyright 2018 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+
+import * as Lint from "../index";
+import { isTypeFlagSet } from 'tsutils';
+
+export class Rule extends Lint.Rules.TypedRule {
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "strict-string-expressions",
+        description: 'Disable implicit toString() calls',
+        descriptionDetails: Lint.Utils.dedent`
+            Require explicit toString() call for variables used in strings. By default only strings are allowed.
+
+            The following nodes are checked:
+
+            * String literals ("foo" + bar)
+            * ES6 templates (\`foo \${bar}\`)`,
+        type: "functionality",
+        typescriptOnly: true,
+        requiresTypeInfo: true,
+        options: [],
+        optionExamples: [true],
+        optionsDescription: "Not configurable.",
+        hasFix: true
+    };
+
+    public static CONVERSION_REQUIRED = 'Explicit conversion to string type required';
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk, undefined, program.getTypeChecker());
+    }
+}
+
+function walk(ctx: Lint.WalkContext<undefined>, checker: ts.TypeChecker): void {
+    const { sourceFile } = ctx;
+    ts.forEachChild(sourceFile, function cb(node: ts.Node): void {
+        switch (node.kind) {
+            case ts.SyntaxKind.BinaryExpression: {
+                const binaryExpr = node as ts.BinaryExpression;
+                if (binaryExpr.operatorToken.kind === ts.SyntaxKind.PlusToken) {
+                    const leftIsString = isTypeFlagSet(checker.getTypeAtLocation(binaryExpr.left), ts.TypeFlags.StringLike);
+                    const rightIsString = isTypeFlagSet(checker.getTypeAtLocation(binaryExpr.right), ts.TypeFlags.StringLike);
+                    const leftIsFailed = !leftIsString && rightIsString;
+                    const rightIsFailed = leftIsString && !rightIsString;
+                    if (leftIsFailed || rightIsFailed) {
+                        const expression = leftIsFailed ? binaryExpr.left : binaryExpr.right;
+                        addFailure(binaryExpr, expression);
+                    }
+                }
+                break;
+            }
+            case ts.SyntaxKind.TemplateSpan: {
+                const templateSpanNode = node as ts.TemplateSpan;
+                const type = checker.getTypeAtLocation(templateSpanNode.expression);
+                const isString = isTypeFlagSet(type, ts.TypeFlags.StringLike);
+                if (!isString) {
+                    const { expression } = templateSpanNode;
+                    addFailure(templateSpanNode, expression);
+                }
+                break;
+            }
+        }
+        return ts.forEachChild(node, cb);
+    });
+
+    function addFailure (
+        node: ts.Node,
+        expression: ts.Expression,
+    ) {
+        const fix = Lint.Replacement.replaceFromTo(
+            expression.getStart(),
+            expression.end,
+            `String(${expression.getText()})`
+        );
+        ctx.addFailureAtNode(node, Rule.CONVERSION_REQUIRED, fix);
+    }
+}

test/rules/strict-string-expressions/test.ts.fix

@@ -0,0 +1,87 @@
+  const fooStr: string = 'foo';
+  const fooNumber = 2;
+  class FooClass {}
+  class ClassWithToString {
+      public static toString () { return ''; }
+      public toString () { return ''; }
+  }
+  const classWithToString = new ClassWithToString();
+  const FooStr = new String('foo');
+  const fooArr = ['foo'];
+  const emptyArr = [];
+
+  `foo`
+  `${fooStr}`
+  `${String(fooNumber)}`
+  `${String(FooClass)}`
+  `${String(ClassWithToString)}`
+  `${String(classWithToString)}`
+  `${String(FooStr)}`
+  `${String(fooArr)}`
+  `${String(emptyArr)}`
+
+  `${String(fooStr)}`
+  `${String(fooNumber)}`
+  `${String(FooClass)}`
+  `${String(ClassWithToString)}`
+  `${String(classWithToString)}`
+  `${String(FooStr)}`
+  `${String(fooArr)}`
+  `${String(emptyArr)}`
+
+  `${fooStr.toString()}`
+  `${fooNumber.toString()}`
+  `${FooClass.toString()}`
+  `${ClassWithToString.toString()}`
+  `${classWithToString.toString()}`
+  `${FooStr.toString()}`
+  `${fooArr.toString()}`
+  `${emptyArr.toString()}`
+
+  'str' + fooStr + 'str'
+  'str' + String(fooNumber) + 'str'
+  'str' + String(FooClass) + 'str'
+  'str' + String(ClassWithToString) + 'str'
+  'str' + String(classWithToString) + 'str'
+  'str' + String(FooStr) + 'str'
+  'str' + String(fooArr) + 'str'
+  'str' + String(emptyArr) + 'str'
+
+  'str' + String(fooStr) + 'str'
+  'str' + String(fooNumber) + 'str'
+  'str' + String(FooClass) + 'str'
+  'str' + String(ClassWithToString) + 'str'
+  'str' + String(classWithToString) + 'str'
+  'str' + String(FooStr) + 'str'
+  'str' + String(fooArr) + 'str'
+  'str' + String(emptyArr) + 'str'
+
+  'str' + fooStr.toString() + 'str'
+  'str' + fooNumber.toString() + 'str'
+  'str' + FooClass.toString() + 'str'
+  'str' + ClassWithToString.toString() + 'str'
+  'str' + classWithToString.toString() + 'str'
+  'str' + FooStr.toString() + 'str'
+  'str' + fooArr.toString() + 'str'
+  'str' + emptyArr.toString() + 'str'
+
+  const barFooStrOrUndef: string | undefined;
+  const barFooStrOrNull: string | null;
+
+  `${String(barFooStrOrUndef)}`
+  `${String(barFooStrOrNull)}`
+
+  `${String(barFooStrOrUndef)}`
+  `${String(barFooStrOrNull)}`
+
+  `${barFooStrOrUndef.toString()}`
+  `${barFooStrOrNull.toString()}`
+
+  'str' + String(barFooStrOrUndef) + 'str'
+  'str' + String(barFooStrOrNull) + 'str'
+
+  'str' + String(barFooStrOrUndef) + 'str'
+  'str' + String(barFooStrOrNull) + 'str'
+
+  'str' + barFooStrOrUndef.toString() + 'str'
+  'str' + barFooStrOrNull.toString() + 'str'

test/rules/strict-string-expressions/test.ts.lint

@@ -0,0 +1,105 @@
+  const fooStr: string = 'foo';
+  const fooNumber = 2;
+  class FooClass {}
+  class ClassWithToString {
+      public static toString () { return ''; }
+      public toString () { return ''; }
+  }
+  const classWithToString = new ClassWithToString();
+  const FooStr = new String('foo');
+  const fooArr = ['foo'];
+  const emptyArr = [];
+
+  `foo`
+  `${fooStr}`
+  `${fooNumber}`
+     ~~~~~~~~~~~ [Explicit conversion to string type required]
+  `${FooClass}`
+     ~~~~~~~~~~ [Explicit conversion to string type required]
+  `${ClassWithToString}`
+     ~~~~~~~~~~~~~~~~~~~ [Explicit conversion to string type required]
+  `${classWithToString}`
+     ~~~~~~~~~~~~~~~~~~~ [Explicit conversion to string type required]
+  `${FooStr}`
+     ~~~~~~~~ [Explicit conversion to string type required]
+  `${fooArr}`
+     ~~~~~~~~ [Explicit conversion to string type required]
+  `${emptyArr}`
+     ~~~~~~~~~~ [Explicit conversion to string type required]
+
+  `${String(fooStr)}`
+  `${String(fooNumber)}`
+  `${String(FooClass)}`
+  `${String(ClassWithToString)}`
+  `${String(classWithToString)}`
+  `${String(FooStr)}`
+  `${String(fooArr)}`
+  `${String(emptyArr)}`
+
+  `${fooStr.toString()}`
+  `${fooNumber.toString()}`
+  `${FooClass.toString()}`
+  `${ClassWithToString.toString()}`
+  `${classWithToString.toString()}`
+  `${FooStr.toString()}`
+  `${fooArr.toString()}`
+  `${emptyArr.toString()}`
+
+  'str' + fooStr + 'str'
+  'str' + fooNumber + 'str'
+  ~~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + FooClass + 'str'
+  ~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + ClassWithToString + 'str'
+  ~~~~~~~~~~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + classWithToString + 'str'
+  ~~~~~~~~~~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + FooStr + 'str'
+  ~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + fooArr + 'str'
+  ~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + emptyArr + 'str'
+  ~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+
+  'str' + String(fooStr) + 'str'
+  'str' + String(fooNumber) + 'str'
+  'str' + String(FooClass) + 'str'
+  'str' + String(ClassWithToString) + 'str'
+  'str' + String(classWithToString) + 'str'
+  'str' + String(FooStr) + 'str'
+  'str' + String(fooArr) + 'str'
+  'str' + String(emptyArr) + 'str'
+
+  'str' + fooStr.toString() + 'str'
+  'str' + fooNumber.toString() + 'str'
+  'str' + FooClass.toString() + 'str'
+  'str' + ClassWithToString.toString() + 'str'
+  'str' + classWithToString.toString() + 'str'
+  'str' + FooStr.toString() + 'str'
+  'str' + fooArr.toString() + 'str'
+  'str' + emptyArr.toString() + 'str'
+
+  const barFooStrOrUndef: string | undefined;
+  const barFooStrOrNull: string | null;
+
+  `${barFooStrOrUndef}`
+     ~~~~~~~~~~~~~~~~~~ [Explicit conversion to string type required]
+  `${barFooStrOrNull}`
+     ~~~~~~~~~~~~~~~~~ [Explicit conversion to string type required]
+
+  `${String(barFooStrOrUndef)}`
+  `${String(barFooStrOrNull)}`
+
+  `${barFooStrOrUndef.toString()}`
+  `${barFooStrOrNull.toString()}`
+
+  'str' + barFooStrOrUndef + 'str'
+  ~~~~~~~~~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+  'str' + barFooStrOrNull + 'str'
+  ~~~~~~~~~~~~~~~~~~~~~~~         [Explicit conversion to string type required]
+
+  'str' + String(barFooStrOrUndef) + 'str'
+  'str' + String(barFooStrOrNull) + 'str'
+
+  'str' + barFooStrOrUndef.toString() + 'str'
+  'str' + barFooStrOrNull.toString() + 'str'

test/rules/strict-string-expressions/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        "strictNullChecks": true
+    }
+}

test/rules/strict-string-expressions/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "strict-string-expressions": true
+  }
+}