Implement custom no-magic-numbers rule that doesn't include magic numbers passed into BigNumber instantiations (e.g const amount = new BigNumber(5); )

2 files changed, 78 insertions, 1 deletions

diff --git a/packages/tslint-config/package.json b/packages/tslint-config/package.json
index 04e1ba2b6..33132210c 100644
--- a/packages/tslint-config/package.json
+++ b/packages/tslint-config/package.json
@@ -41,7 +41,8 @@
         "lodash": "^4.17.4",
         "tslint": "5.8.0",
         "tslint-eslint-rules": "^4.1.1",
-        "tslint-react": "^3.2.0"
+        "tslint-react": "^3.2.0",
+        "tsutils": "^2.12.1"
     },
     "publishConfig": {
         "access": "public"
diff --git a/packages/tslint-config/rules/customNoMagicNumbersRule.ts b/packages/tslint-config/rules/customNoMagicNumbersRule.ts
new file mode 100644
index 000000000..e358221eb
--- /dev/null
+++ b/packages/tslint-config/rules/customNoMagicNumbersRule.ts
@@ -0,0 +1,76 @@
+import * as Lint from 'tslint';
+import { isPrefixUnaryExpression } from 'tsutils';
+import * as ts from 'typescript';
+
+/**
+ * A modified version of the no-magic-numbers rule that allows for magic numbers
+ * when instantiating a BigNumber instance.
+ * E.g We want to be able to write:
+ *     const amount = new BigNumber(5);
+ * Original source: https://github.com/palantir/tslint/blob/42b058a6baa688f8be8558b277eb056c3ff79818/src/rules/noMagicNumbersRule.ts
+ */
+export class Rule extends Lint.Rules.AbstractRule {
+    public static ALLOWED_NODES = new Set<ts.SyntaxKind>([
+        ts.SyntaxKind.ExportAssignment,
+        ts.SyntaxKind.FirstAssignment,
+        ts.SyntaxKind.LastAssignment,
+        ts.SyntaxKind.PropertyAssignment,
+        ts.SyntaxKind.ShorthandPropertyAssignment,
+        ts.SyntaxKind.VariableDeclaration,
+        ts.SyntaxKind.VariableDeclarationList,
+        ts.SyntaxKind.EnumMember,
+        ts.SyntaxKind.PropertyDeclaration,
+        ts.SyntaxKind.Parameter,
+    ]);
+
+    public static DEFAULT_ALLOWED = [-1, 0, 1];
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        const allowedNumbers = this.ruleArguments.length > 0 ? this.ruleArguments : Rule.DEFAULT_ALLOWED;
+        return this.applyWithWalker(
+            new CustomNoMagicNumbersWalker(sourceFile, this.ruleName, new Set(allowedNumbers.map(String))),
+        );
+    }
+}
+
+// tslint:disable-next-line:max-classes-per-file
+class CustomNoMagicNumbersWalker extends Lint.AbstractWalker<Set<string>> {
+    public static FAILURE_STRING = "'magic numbers' are not allowed";
+    private static _isNegativeNumberLiteral(
+        node: ts.Node,
+    ): node is ts.PrefixUnaryExpression & { operand: ts.NumericLiteral } {
+        return (
+            isPrefixUnaryExpression(node) &&
+            node.operator === ts.SyntaxKind.MinusToken &&
+            node.operand.kind === ts.SyntaxKind.NumericLiteral
+        );
+    }
+    public walk(sourceFile: ts.SourceFile): void {
+        const cb = (node: ts.Node): void => {
+            if (node.kind === ts.SyntaxKind.NumericLiteral) {
+                return this.checkNumericLiteral(node, (node as ts.NumericLiteral).text);
+            }
+            if (CustomNoMagicNumbersWalker._isNegativeNumberLiteral(node)) {
+                return this.checkNumericLiteral(node, `-${(node.operand as ts.NumericLiteral).text}`);
+            }
+            return ts.forEachChild(node, cb);
+        };
+        return ts.forEachChild(sourceFile, cb);
+    }
+
+    // tslint:disable:no-non-null-assertion
+    // tslint:disable-next-line:underscore-private-and-protected
+    private checkNumericLiteral(node: ts.Node, num: string): void {
+        if (!Rule.ALLOWED_NODES.has(node.parent!.kind) && !this.options.has(num)) {
+            if (node.parent!.kind === ts.SyntaxKind.NewExpression) {
+                const className = (node.parent! as any).expression.escapedText;
+                const BIG_NUMBER_NEW_EXPRESSION = 'BigNumber';
+                if (className === BIG_NUMBER_NEW_EXPRESSION) {
+                    return; // noop
+                }
+            }
+            this.addFailureAtNode(node, CustomNoMagicNumbersWalker.FAILURE_STRING);
+        }
+    }
+    // tslint:enable:no-non-null-assertion
+}