Implement boolean variable naming custom TSLint rule

1 files changed, 69 insertions, 0 deletions

diff --git a/packages/tslint-config/rules/booleanNamingRule.ts b/packages/tslint-config/rules/booleanNamingRule.ts
new file mode 100644
index 000000000..bc0b42e71
--- /dev/null
+++ b/packages/tslint-config/rules/booleanNamingRule.ts
@@ -0,0 +1,69 @@
+import * as _ from 'lodash';
+import * as Lint from 'tslint';
+import * as ts from 'typescript';
+
+const VALID_BOOLEAN_PREFIXES = ['is', 'does', 'should', 'was', 'has', 'can', 'did', 'would'];
+
+export class Rule extends Lint.Rules.TypedRule {
+    public static FAILURE_STRING = `Boolean variable names should begin with: ${VALID_BOOLEAN_PREFIXES.join(', ')}`;
+
+    public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+        return this.applyWithFunction(sourceFile, walk, undefined, program.getTypeChecker());
+    }
+}
+
+function walk(ctx: Lint.WalkContext<void>, tc: ts.TypeChecker): void {
+    traverse(ctx.sourceFile);
+
+    function traverse(node: ts.Node): void {
+        checkNodeForViolations(ctx, node, tc);
+        return ts.forEachChild(node, traverse);
+    }
+}
+
+function checkNodeForViolations(ctx: Lint.WalkContext<void>, node: ts.Node, tc: ts.TypeChecker): void {
+    switch (node.kind) {
+        // Handle: const { timestamp } = ...
+        case ts.SyntaxKind.BindingElement: {
+            const bindingElementNode = node as ts.BindingElement;
+            if (bindingElementNode.name.kind === ts.SyntaxKind.Identifier) {
+                handleBooleanNaming(bindingElementNode, tc, ctx);
+            }
+            break;
+        }
+
+        // Handle regular assignments: const block = ...
+        case ts.SyntaxKind.VariableDeclaration:
+            const variableDeclarationNode = node as ts.VariableDeclaration;
+            if (variableDeclarationNode.name.kind === ts.SyntaxKind.Identifier) {
+                handleBooleanNaming(node as ts.VariableDeclaration, tc, ctx);
+            }
+            break;
+
+        default:
+        // noop
+    }
+}
+
+function handleBooleanNaming(
+    node: ts.VariableDeclaration | ts.BindingElement,
+    tc: ts.TypeChecker,
+    ctx: Lint.WalkContext<void>,
+): void {
+    const nodeName = node.name;
+    const variableName = nodeName.getText();
+    const lowercasedName = _.toLower(variableName);
+    // tslint:disable-next-line
+    const typeNode = tc.getTypeAtLocation(node);
+    const typeName = (typeNode as any).intrinsicName;
+    if (typeName === 'boolean') {
+        const hasProperName = !_.isUndefined(
+            _.find(VALID_BOOLEAN_PREFIXES, prefix => {
+                return _.startsWith(lowercasedName, prefix);
+            }),
+        );
+        if (!hasProperName) {
+            ctx.addFailureAtNode(node, Rule.FAILURE_STRING);
+        }
+    }
+}