Update --infer-tsconfig to skip the allowJs option when there exist TS files (#90)

Fixes #87. Previously, we always included the `allowJs` option when
using `--infer-tsconfig`. However, this behavior was undesirable because
TypeScript package repos include a large amount of generated JavaScript
code that should not be indexed.  This commit changes the behavior so
that we only use `allowJs` when the project doesn't have any TypeScript
files.

For example, the `npm/typescript` package (for the TypeScript compiler
itself) times out when we index with `allowJs` while it completes in
a few seconds without `allowJs`.  It's OK to skip the JavaScript files
since the TypeScript files include the definitions for the JavaScript
code.

Author: olafurpg

snapshots/inferTsConfig/js-project/hello.js

@@ -0,0 +1,21 @@
+import { join } from 'path'
+import * as process from 'process'
+
+import { test } from 'uvu'
+
+import { allowJsConfig, inferTsConfig, noJsConfig } from './inferTsConfig'
+
+const inputDirectory = join(process.cwd(), 'snapshots', 'inferTsConfig')
+
+function checkDirectory(name: string, expected: string): void {
+  test(name, () => {
+    const directory = join(inputDirectory, name)
+    const obtained = inferTsConfig(directory)
+    if (obtained !== expected) {
+      throw new Error(`expected ('${expected}') != obtained ('${obtained}')`)
+    }
+  })
+}
+
+checkDirectory('js-project', allowJsConfig)
+checkDirectory('ts-project', noJsConfig)

snapshots/inferTsConfig/ts-project/hello.js

@@ -0,0 +1,55 @@
+import * as fs from 'fs'
+import * as path from 'path'
+
+/**
+ * To limit the risk of making the `inferTsConfig` run for a very long time, we
+ * stop the file traversal after visiting this number of files.
+ */
+const maximumFileTraversalCount = 1_000
+
+/** The TS config we use to index JavaScript files. */
+export const allowJsConfig = '{"compilerOptions":{"allowJs":true}}'
+
+/** The TS config we use to index only TypeScript files. */
+export const noJsConfig = '{}'
+
+/**
+ * Returns the configuration that should be used for tsconfig.json in the provided path.
+ *
+ * If the directory contains at least one `*.{ts,tsx}` file then the config will be empty (`{}`).
+ * If the directory doesn't contains one `*.{ts,tsx}` file then the config will
+ */
+export function inferTsConfig(projectPath: string): string {
+  let hasTypeScriptFile = false
+  let hasJavaScriptFile = false
+  let visitedFileCount = 0
+  const visitPath = (directory: string): { stop: boolean } => {
+    if (directory.endsWith('.ts') || directory.endsWith('.tsx')) {
+      hasTypeScriptFile = true
+      return { stop: true }
+    }
+    if (directory.endsWith('.js') || directory.endsWith('.jsx')) {
+      hasJavaScriptFile = true
+    }
+    if (!fs.statSync(directory).isDirectory()) {
+      return { stop: false }
+    }
+    for (const child of fs.readdirSync(directory)) {
+      visitedFileCount++
+      if (visitedFileCount > maximumFileTraversalCount) {
+        return { stop: true }
+      }
+      const fullPath = path.resolve(directory, child)
+      const recursiveWalk = visitPath(fullPath)
+      if (recursiveWalk.stop) {
+        return recursiveWalk
+      }
+    }
+    return { stop: false }
+  }
+  visitPath(projectPath)
+  if (hasTypeScriptFile || !hasJavaScriptFile) {
+    return noJsConfig
+  }
+  return allowJsConfig
+}

snapshots/inferTsConfig/ts-project/hello.ts

@@ -9,6 +9,7 @@ import * as ts from 'typescript'
 
 import packageJson from '../package.json'
 
+import { inferTsConfig } from './inferTsConfig'
 import * as lsif from './lsif'
 import { ProjectIndexer } from './ProjectIndexer'
 
@@ -146,7 +147,7 @@ function indexSingleProject(options: ProjectOptions): void {
     }
     if (!ts.sys.fileExists(tsconfigFileName)) {
       if (options.inferTsconfig) {
-        fs.writeFileSync(tsconfigFileName, '{"compilerOptions":{"allowJs":true}}')
+        fs.writeFileSync(tsconfigFileName, inferTsConfig(projectPath))
       } else {
         console.error(`- ${options.projectDisplayName} (missing tsconfig.json)`)
         return