feat: add collectVariableUsage API (#274)

## PR Checklist

- [x] Addresses an existing open issue: fixes #263
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/ts-api-utils/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/ts-api-utils/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

Directly ports the exported public `collectVariableUsage` function from
`tsutils`. Adds in some unit test coverage too.

I'd wanted to refactor its source to be less reliant on class
hierarchies... but there's a lot going on there. Out of scope for now. I
did apply a few touchups:
* Changed "soft" privates to use `#`.
* Renamed `VariableInfo` to `UsageInfo`.
* It's used both for types and values, so referring to them as
"variables" was confusing to me.
* Please shout at me if you can think of a better name or believe the
original name to be better!
* Switches the `const enum`s to just `enum`s.
* Adds test coverage for the most common cases.
* It's not super thorough, so if you spot some logic you think should be
tested, shout at me and I'm happy to add it in if I can

Author: JoshuaKGoldberg

.eslintrc.cjs

@@ -32,6 +32,7 @@ module.exports = {
 				"@typescript-eslint/explicit-module-boundary-types": "error",
 
 				// TODO?
+				"@typescript-eslint/prefer-literal-enum-member": "off",
 				"@typescript-eslint/no-confusing-void-expression": "off",
 				"@typescript-eslint/no-non-null-assertion": "off",
 				"@typescript-eslint/no-unnecessary-condition": "off",
@@ -72,6 +73,10 @@ module.exports = {
 	root: true,
 	rules: {
 		// These off-by-default rules work well for this repo and we like them on.
+		"@typescript-eslint/no-unused-vars": [
+			"error",
+			{ argsIgnorePattern: "^_", caughtErrors: "all" },
+		],
 		"import/extensions": ["error"],
 		"import/no-useless-path-segments": [
 			"error",

cspell.json

@@ -24,7 +24,9 @@
 		"konamimojisplosion",
 		"lcov",
 		"packagejson",
+		"phenomnomnominal",
 		"quickstart",
+		"tsquery",
 		"tsup",
 		"tsutils",
 		"tsvfs",

package.json

@@ -49,6 +49,7 @@
 		"*": "prettier --ignore-unknown --write"
 	},
 	"devDependencies": {
+		"@phenomnomnominal/tsquery": "^6.1.3",
 		"@typescript-eslint/eslint-plugin": "^6.4.0",
 		"@typescript-eslint/parser": "6.5.0",
 		"@typescript/vfs": "^1.5.0",

pnpm-lock.yaml

@@ -7,3 +7,4 @@ export * from "./scopes";
 export * from "./syntax";
 export * from "./tokens";
 export * from "./types";
+export * from "./usage";

src/index.ts

@@ -15,11 +15,11 @@ import ts from "typescript";
  * ```
  */
 export function includesModifier(
-	modifiers: Iterable<ts.Modifier> | undefined,
+	modifiers: Iterable<ts.ModifierLike> | undefined,
 	...kinds: ts.ModifierSyntaxKind[]
 ): boolean {
 	if (modifiers === undefined) return false;
 	for (const modifier of modifiers)
-		if (kinds.includes(modifier.kind)) return true;
+		if (kinds.includes(modifier.kind as ts.ModifierSyntaxKind)) return true;
 	return false;
 }

src/modifiers.ts

@@ -4,11 +4,7 @@ import ts from "typescript";
 export function createNodeAndSourceFile<Node extends ts.Node>(
 	sourceText: string,
 ): { node: Node; sourceFile: ts.SourceFile } {
-	const sourceFile = ts.createSourceFile(
-		"file.tsx",
-		sourceText,
-		ts.ScriptTarget.ESNext,
-	);
+	const sourceFile = createSourceFile(sourceText);
 	const statement = sourceFile.statements.at(-1)!;
 
 	const node = (ts.isExpressionStatement(statement)
@@ -18,6 +14,15 @@ export function createNodeAndSourceFile<Node extends ts.Node>(
 	return { node, sourceFile };
 }
 
+export function createSourceFile(sourceText: string): ts.SourceFile {
+	return ts.createSourceFile(
+		"file.tsx",
+		sourceText,
+		ts.ScriptTarget.ESNext,
+		true,
+	);
+}
+
 export function createNode<Node extends ts.Node>(
 	nodeOrSourceText: Node | string,
 ): Node {

src/test/utils.ts

@@ -0,0 +1,72 @@
+// Code largely based on https://github.com/ajafff/tsutils
+// Original license: https://github.com/ajafff/tsutils/blob/26b195358ec36d59f00333115aa3ffd9611ca78b/LICENSE
+
+import ts from "typescript";
+
+import { isFunctionScopeBoundary } from "../scopes";
+import { DeclarationDomain } from "./declarations";
+import type { EnumScope, NamespaceScope } from "./scopes";
+import { InternalUsageInfo, Usage, UsageInfoCallback } from "./usage";
+
+export enum ScopeBoundary {
+	None = 0,
+	Function = 1,
+	Block = 2,
+	Type = 4,
+	ConditionalType = 8,
+}
+
+export enum ScopeBoundarySelector {
+	Function = ScopeBoundary.Function,
+	Block = ScopeBoundarySelector.Function | ScopeBoundary.Block,
+	Type = ScopeBoundarySelector.Block | ScopeBoundary.Type,
+	InferType = ScopeBoundary.ConditionalType,
+}
+
+export interface Scope {
+	addUse(use: Usage, scope?: Scope): void;
+	addVariable(
+		identifier: string,
+		name: ts.PropertyName,
+		selector: ScopeBoundarySelector,
+		exported: boolean,
+		domain: DeclarationDomain,
+	): void;
+	createOrReuseEnumScope(name: string, exported: boolean): EnumScope;
+	createOrReuseNamespaceScope(
+		name: string,
+		exported: boolean,
+		ambient: boolean,
+		hasExportStatement: boolean,
+	): NamespaceScope;
+	end(cb: UsageInfoCallback): void;
+	getDestinationScope(selector: ScopeBoundarySelector): Scope;
+	getFunctionScope(): Scope;
+	getVariables(): Map<string, InternalUsageInfo>;
+	markExported(name: ts.Identifier, as?: ts.Identifier): void;
+}
+
+export function isBlockScopeBoundary(node: ts.Node): ScopeBoundary {
+	switch (node.kind) {
+		case ts.SyntaxKind.Block: {
+			const parent = node.parent;
+			return parent.kind !== ts.SyntaxKind.CatchClause &&
+				// blocks inside SourceFile are block scope boundaries
+				(parent.kind === ts.SyntaxKind.SourceFile ||
+					// blocks that are direct children of a function scope boundary are no scope boundary
+					// for example the FunctionBlock is part of the function scope of the containing function
+					!isFunctionScopeBoundary(parent))
+				? ScopeBoundary.Block
+				: ScopeBoundary.None;
+		}
+		case ts.SyntaxKind.ForStatement:
+		case ts.SyntaxKind.ForInStatement:
+		case ts.SyntaxKind.ForOfStatement:
+		case ts.SyntaxKind.CaseBlock:
+		case ts.SyntaxKind.CatchClause:
+		case ts.SyntaxKind.WithStatement:
+			return ScopeBoundary.Block;
+		default:
+			return ScopeBoundary.None;
+	}
+}