Clean up prefer-for-of rule #2348

andy-hanson · 2017-03-15T03:31:03Z

PR checklist

Addresses an existing issue: #0000
New feature, bugfix, or enhancement
- Includes tests
Documentation update

Overview of change:

Don't unnecessarily use a BlockScopeAwareRuleWalker, just store a stack of for-loop scopes.

Don't unnecessarily use a BlockScopeAwareRuleWalker, just store a stack of for-loop scopes

ajafff

don't know how to say this in a nice way ...
this code still looks pretty bad

I left some comments on the really bad parts. I will review again after these changes

ajafff · 2017-03-24T13:50:45Z

src/rules/preferForOfRule.ts

-                        return true;
-                    }
+    } else if (node.kind === ts.SyntaxKind.PostfixUnaryExpression) {
+        const incrementor = node as ts.PostfixUnaryExpression;


could be joined with the if block above as they do exactly the same

ajafff · 2017-03-24T13:51:23Z

src/rules/preferForOfRule.ts

-                    }
+    } else if (node.kind === ts.SyntaxKind.PostfixUnaryExpression) {
+        const incrementor = node as ts.PostfixUnaryExpression;
+        if (incrementor.operator === ts.SyntaxKind.PlusPlusToken && incrementor.operand.getText() === indexVariableName) {


just return, no need for an if

ajafff · 2017-03-24T13:53:19Z

src/rules/preferForOfRule.ts

+    // ensure variable is incremented
+    if (node.kind === ts.SyntaxKind.PrefixUnaryExpression) {
+        const incrementor = node as ts.PrefixUnaryExpression;
+        if (incrementor.operator === ts.SyntaxKind.PlusPlusToken && incrementor.operand.getText() === indexVariableName) {


you could replace incrementor.operand.getText() === indexVariableName with isIdentifier(incrementor.operand) && incrementor.operand.text === indexVariableName

maybe make this a function because you also need it below

ajafff · 2017-03-24T13:53:51Z

src/rules/preferForOfRule.ts

-        if (node == null) {
-            return false;
+    // ensure variable is incremented
+    if (node.kind === ts.SyntaxKind.PrefixUnaryExpression) {


use typeguards?

ajafff · 2017-03-24T13:55:58Z

src/rules/preferForOfRule.ts

+        }
+    } else if (node.kind === ts.SyntaxKind.BinaryExpression) {
+        const binaryExpression = node as ts.BinaryExpression;
+        if (binaryExpression.operatorToken.getText() === "+="


operatorToken.kind === ts.SyntaxKind.PlusEqualsToken
same below with EqualsToken and PlusToken

ajafff · 2017-03-24T13:58:46Z

src/rules/preferForOfRule.ts

+        const binaryExpression = node as ts.BinaryExpression;
+        if (binaryExpression.operatorToken.getText() === "+="
+            && binaryExpression.left.getText() === indexVariableName
+            && binaryExpression.right.getText() === "1") {


isNumericLiteral(binaryExpression.right) && binaryExpression.right.text === "1"

make this a function a reuse it for the 2 conditions below, too

ajafff · 2017-03-24T14:12:06Z

src/rules/preferForOfRule.ts

+    let indexVariable: ts.Identifier | undefined;
+
+    // assign `indexVariableName` if initializer is simple and starts at 0
+    if (forLoop.initializer && forLoop.initializer.kind === ts.SyntaxKind.VariableDeclarationList) {


if (forLoop.initializer && isVariableDeclarationList(forLoop.initializer) && forLoop.initializer.declarations.length === 1) { const declaration = forLoop.initializer.declarations[0]; if (declaration.name.kind === ts.SyntaxKind.Identifier && declaration.initializer !== undefined && isNumericLiteral(declaration.initializer) && declaration.initializer.text === "0") { indexVariable = declaration.name; indexVariableName = indexVariable.text; } }

ajafff · 2017-03-24T14:16:03Z

src/rules/preferForOfRule.ts

+    // ensure `for` condition
+    if (!indexVariableName
+        || !forLoop.condition
+        || forLoop.condition.kind !== ts.SyntaxKind.BinaryExpression


!isBinaryExpression(forLoop.condition) || !isVariable(forLoop.condition.left, indexVariableName) || // see my other comments regarding indexVariableName forLoop.condition.operatorToken.kind !== ts.SyntaxKind.LessThanToken || // condition from line 159 !isPropertyAccessExpression(forLoop.condition.right) || forLoop.condition.right.name.text !== "length"

ajafff · 2017-03-24T14:21:12Z

src/rules/preferForOfRule.ts

+        // store `for` loop state
+        const state: IncrementorState = {
+            indexVariableName,
+            arrayToken: arrayToken as ts.Identifier,


arrayToken is not guaranteed to be ts.Identifier

ajafff · 2017-03-24T14:23:25Z

src/rules/preferForOfRule.ts

+        if (state.arrayToken.getText() !== arrayIdentifier.getText()) {
+            // iterator used in array other than one iterated over
+            state.onlyArrayReadAccess = false;
+        } else if (elementAccess.parent && isAssignment(elementAccess.parent)) {


elementAccess.parent is never undefined, so you can simply assert it

ajafff · 2017-03-28T08:35:48Z

AFAICT the rule will bail out if you use an identifier with the same name as the index variable somewhere inside the loop body. That's no blocker for now as the old implementation behaved the same I guess.

for (let i = 0; i < arr.length; ++i) {
    {
        let i; // i is not used in element access, the rule bails out
    }
    class Foo {
        private i; // same as above
        constructor(i: number) {} // same as above
    }
    let foo: { i: number } = { i: 1 }; // same as above for both identifiers
}

ajafff

code looks much better now, thanks

andy-hanson force-pushed the prefer-for-of branch 2 times, most recently from 42a503c to 7a0b9b7 Compare March 15, 2017 03:33

Clean up prefer-for-of

f9d7577

Don't unnecessarily use a BlockScopeAwareRuleWalker, just store a stack of for-loop scopes

andy-hanson force-pushed the prefer-for-of branch from 7a0b9b7 to f9d7577 Compare March 15, 2017 03:43

ajafff suggested changes Mar 24, 2017

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Clean up code

32633fd

ajafff approved these changes Mar 28, 2017

View reviewed changes

adidahiya approved these changes Mar 29, 2017

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adidahiya changed the title ~~Clean up prefer-for-of~~ Clean up prefer-for-of rule Mar 29, 2017

adidahiya merged commit d030e8f into palantir:master Mar 29, 2017

renovate-bot mentioned this pull request Mar 29, 2017

Update dependency tslint to version 5.x singapore/lint-condo#263

Merged

andy-hanson deleted the prefer-for-of branch March 30, 2017 00:12

andy-hanson mentioned this pull request Apr 8, 2017

Using (Block/)ScopeAwareRuleWalker with typed programs #2514

Closed

ajafff mentioned this pull request Jul 2, 2017

Update to latest tsutils #2984

Merged

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Clean up prefer-for-of rule #2348

Clean up prefer-for-of rule #2348

andy-hanson commented Mar 15, 2017

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Clean up prefer-for-of rule #2348

Clean up prefer-for-of rule #2348

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andy-hanson commented Mar 15, 2017

PR checklist

Overview of change:

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ajafff commented Mar 28, 2017

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