[unnecessary-else] Allow "else if" statements with new rule option (#…

…4599)

src/rules/unnecessaryElseRule.ts

@@ -21,15 +21,24 @@ import * as Lint from "../index";
 
 import { codeExamples } from "./code-examples/unnecessaryElse.examples";
 
+const OPTION_ALLOW_ELSE_IF = "allow-else-if";
+
 export class Rule extends Lint.Rules.AbstractRule {
     /* tslint:disable:object-literal-sort-keys */
     public static metadata: Lint.IRuleMetadata = {
         description: Lint.Utils.dedent`
         Disallows \`else\` blocks following \`if\` blocks ending with a \`break\`, \`continue\`, \`return\`, or \`throw\` statement.`,
         descriptionDetails: "",
-        optionExamples: [true],
-        options: null,
-        optionsDescription: "Not configurable.",
+        optionExamples: [true, [true, { [OPTION_ALLOW_ELSE_IF]: true }]],
+        options: {
+            type: "object",
+            properties: {
+                [OPTION_ALLOW_ELSE_IF]: { type: "boolean" },
+            },
+        },
+        optionsDescription: Lint.Utils.dedent`
+            You can optionally specify the option \`"${OPTION_ALLOW_ELSE_IF}"\` to allow "else if" statements.
+        `,
         rationale: Lint.Utils.dedent`
         When an \`if\` block is guaranteed to exit control flow when entered,
         it is unnecessary to add an \`else\` statement.
@@ -46,7 +55,11 @@ export class Rule extends Lint.Rules.AbstractRule {
     }
 
     public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
-        return this.applyWithFunction(sourceFile, walk);
+        return this.applyWithFunction(
+            sourceFile,
+            walk,
+            parseOptions(this.ruleArguments[0] as Partial<Options> | undefined),
+        );
     }
 }
 
@@ -55,7 +68,18 @@ interface IJumpAndIfStatement {
     node: ts.IfStatement;
 }
 
-function walk(ctx: Lint.WalkContext): void {
+interface Options {
+    [OPTION_ALLOW_ELSE_IF]: boolean;
+}
+
+function parseOptions(option: Partial<Options> | undefined): Options {
+    return {
+        [OPTION_ALLOW_ELSE_IF]: false,
+        ...option,
+    };
+}
+
+function walk(ctx: Lint.WalkContext<Options>): void {
     const ifStatementStack: IJumpAndIfStatement[] = [];
 
     function visitIfStatement(node: ts.IfStatement) {
@@ -68,7 +92,8 @@ function walk(ctx: Lint.WalkContext): void {
         if (
             jumpStatement !== undefined &&
             node.elseStatement !== undefined &&
-            !recentStackParentMissingJumpStatement()
+            !recentStackParentMissingJumpStatement() &&
+            (!utils.isIfStatement(node.elseStatement) || !ctx.options[OPTION_ALLOW_ELSE_IF])
         ) {
             const elseKeyword = getPositionOfElseKeyword(node, ts.SyntaxKind.ElseKeyword);
             ctx.addFailureAtNode(elseKeyword, Rule.FAILURE_STRING(jumpStatement));

test/rules/unnecessary-else/allow-else-if/test.ts.lint

@@ -0,0 +1,255 @@
+const testReturn = (a) => {
+    if (a===0) {
+       return 0;
+    } else {
+      ~~~~  [return]
+       return a;
+    }
+}
+
+const testReturn = (a) => {
+    if (a===0) return 0;
+    else return a;
+    ~~~~  [return]
+}
+
+const testReturn = (a) => {
+    if (a===0)
+        return 0;
+    else
+    ~~~~  [return]
+        return a;
+}
+
+const testReturn = (a) => {
+    if (a>0) {
+        if (a%2 ===0) {
+        return "even" ;
+        } else {
+          ~~~~  [return]
+            return "odd";
+        }
+    }
+    return "negative";
+}
+
+const testReturn = (a) => {
+    if (a===0) {
+       return 0;
+    }
+    return a;
+}
+
+const testReturn = (a) => {
+    if (a<0) {
+       return;
+    } else if (a>0) {
+        if (a%2 === 0) {
+            return ;
+        } else if (a === 0) {
+            return ;
+        }
+    }
+    return;
+}
+
+const testReturn = (a) => {
+    if (a<0) {
+       return;
+    }
+    if (a===1) {
+        return ;
+    } else {
+      ~~~~  [return]
+        return ;
+    }
+}
+
+const testReturn = (a) => {
+    if (a>0) {
+       if (a%3===0) {
+           return;
+        } else {
+          ~~~~  [return]
+            console.log(a)
+        }
+    }
+    else {
+        console.log("negative");
+    }
+}
+
+const testThrow = (a) => {
+   if ( a===0 ) {
+       throw "error";
+   } else {
+     ~~~~  [throw]
+        return 100/a;
+   }
+}
+
+const testThrow = (a) => {
+    if (a===0)
+        throw "error;
+    else if (a < 0)
+        console.log(100/a);
+}
+
+const testThrow = (a) => {
+    if (a===0)  throw "error;
+    else    console.log(100/a);
+    ~~~~  [throw]
+}
+
+const testThrow = (a) => {
+    switch (a) {
+        case 1:
+            break;
+        case 2:
+            if (true) {
+                throw "error";
+            } else {
+              ~~~~  [throw]
+                break;
+            }
+        default :
+            break;
+    }
+}
+
+const testThrow = (a) => {
+    let i = 1;
+    do  {
+            if (a-i === 0) {
+                throw "error;
+            } else {
+              ~~~~  [throw]
+                console.log(i/a-i);
+            }
+        ++i;
+    }
+}
+
+const testThrow = (a) => {
+   if (a===0) {
+       throw "error";
+   }
+   return 100/a;
+}
+
+const testThrow = (a) => {
+   if (a===0)   throw "error";
+   return 100/a;
+}
+
+const testContinue = () => {
+    for (let i = 1; i < 10; i++) {
+        if (i===8) {
+            continue ;
+        } else {
+          ~~~~ [continue]
+            console.log(i);
+        }
+    }
+}
+
+const testContinue = () => {
+    for (let i = 1; i < 10; i++) {
+        if (i===8)  continue ;
+        else    console.log(i);
+        ~~~~ [continue]
+    }
+}
+
+const testContinue = () => {
+    for (let i = 1; i < 10; i++) {
+        if (i===8)
+            continue ;
+        else
+        ~~~~ [continue]
+            console.log(i);
+    }
+}
+
+const testContinue = () => {
+    for (let i = 1; i < 10; i++) {
+        if (i===4) {
+            continue ;
+        }
+        console.log(i);
+    }
+}
+
+const testContinue = () => {
+    for (let i = 1; i < 10; i++) {
+        if (i===4)
+           continue ;
+        console.log(i);
+    }
+}
+
+const testBreak = (a) => {
+    let i = 0;
+    while(i < 20) {
+        if (i === a) {
+            break ;
+        } else {
+          ~~~~ [break]
+            i++;
+        }
+    }
+    return i-1;
+}
+
+const testBreak = (a) => {
+    let i = 0;
+    while(i < 20) {
+        if (i === a) {
+            break ;
+        }
+        i++;
+    }
+    return i-1;
+}
+
+const testBreak = (a) => {
+    let i = 0;
+    while(i < 20) {
+        if (i === a)
+            break ;
+        i++;
+    }
+    return i-1;
+}
+
+const testBreak = (a) => {
+    let i = 0;
+    while(i < 20) {
+        if (i === a)    break ;
+        i++;
+    }
+    return i-1;
+}
+
+const testBreak = (a) => {
+    let i = 0;
+    while(i < 20) {
+        if (i === a)    break ;
+        else    i++;
+        ~~~~ [break]
+    }
+    return i-1;
+}
+
+const testNoJump = (a) => {
+    if (a % 2 === 0) {
+        console.log(a);
+    } else {
+        console.log(a * 2);
+    }
+}
+
+[return]: The preceding `if` block ends with a `return` statement. This `else` is unnecessary.
+[throw]: The preceding `if` block ends with a `throw` statement. This `else` is unnecessary.
+[break]: The preceding `if` block ends with a `break` statement. This `else` is unnecessary.
+[continue]: The preceding `if` block ends with a `continue` statement. This `else` is unnecessary.

test/rules/unnecessary-else/allow-else-if/tslint.json

@@ -0,0 +1,5 @@
+{
+    "rules": {
+      "unnecessary-else": [true,  { "allow-else-if": true }]
+    }
+}