feat: first approach to find existing eslint config

src/cli/main.ts

@@ -88,6 +88,10 @@ import { findTSLintConfiguration } from "../input/findTSLintConfiguration";
 import { findTypeScriptConfiguration } from "../input/findTypeScriptConfiguration";
 import { importer, ImporterDependencies } from "../input/importer";
 import { mergeLintConfigurations } from "../input/mergeLintConfigurations";
+import {
+    findExistingESLintConfiguration,
+    FindExistingESLintConfigurationDependencies,
+} from "../input/findExistingESLintConfiguration";
 
 const convertFileCommentsDependencies: ConvertFileCommentsDependencies = {
     converters: ruleConverters,
@@ -133,6 +137,10 @@ const findOriginalConfigurationsDependencies: FindOriginalConfigurationsDependen
     mergeLintConfigurations,
 };
 
+const findExistingESLintConfigurationDependencies: FindExistingESLintConfigurationDependencies = {
+    globAsync,
+};
+
 const collectCommentFileNamesDependencies: CollectCommentFileNamesDependencies = {
     findTypeScriptConfiguration: bind(findTypeScriptConfiguration, findConfigurationDependencies),
 };
@@ -216,6 +224,10 @@ const runCliDependencies: RunCliDependencies = {
         findOriginalConfigurations,
         findOriginalConfigurationsDependencies,
     ),
+    findExistingESLintConfiguration: bind(
+        findExistingESLintConfiguration,
+        findExistingESLintConfigurationDependencies,
+    ),
     logger: processLogger,
 };
 

src/cli/runCli.ts

@@ -6,6 +6,7 @@ import { version } from "../../package.json";
 import { Logger } from "../adapters/logger";
 import { SansDependencies } from "../binding";
 import { Converter } from "../converters/types";
+import { findExistingESLintConfiguration } from "../input/findExistingESLintConfiguration";
 import {
     AllOriginalConfigurations,
     findOriginalConfigurations,
@@ -15,6 +16,7 @@ import { ResultStatus, ResultWithStatus, TSLintToESLintSettings } from "../types
 
 export type RunCliDependencies = {
     converters: Converter[];
+    findExistingESLintConfiguration: SansDependencies<typeof findExistingESLintConfiguration>;
     findOriginalConfigurations: SansDependencies<typeof findOriginalConfigurations>;
     logger: Logger;
 };
@@ -41,7 +43,6 @@ export const runCli = async (
         .option("-V, --version", "output the package version");
 
     const parsedArgv = {
-        config: "./.eslintrc.js",
         ...command.parse(rawArgv).opts(),
     } as TSLintToESLintSettings;
 
@@ -51,6 +52,21 @@ export const runCli = async (
         return ResultStatus.Succeeded;
     }
 
+    // 2-B. Lookup the eslint config file `.eslintrc.*` (js, json, yaml) / package.json file
+    const eslintConfiguration = await dependencies.findExistingESLintConfiguration();
+    if (eslintConfiguration.status !== ResultStatus.Succeeded) {
+        logErrorResult(eslintConfiguration, dependencies.logger);
+    } else {
+        if (Array.isArray(eslintConfiguration.data)) {
+            // Pick the first one, it should take into account the order of
+            // preference based on official ESLint Docs.
+            parsedArgv.config = eslintConfiguration.data[0];
+        } else {
+            // TODO: We need to keep the current package.json data
+            parsedArgv.config = "package.json";
+        }
+    }
+
     // 3. Any existing linter and TypeScript configurations are read from disk.
     const originalConfigurations = await dependencies.findOriginalConfigurations(parsedArgv);
     if (originalConfigurations.status !== ResultStatus.Succeeded) {

src/input/findExistingESLintConfiguration.ts

@@ -0,0 +1,40 @@
+import { fsFileSystem } from "../adapters/fsFileSystem";
+import { GlobAsync } from "../adapters/globAsync";
+import { ResultStatus, ResultWithDataStatus } from "../types";
+import { ESLintConfiguration } from "./findESLintConfiguration";
+
+export type FindExistingESLintConfigurationDependencies = {
+    globAsync: GlobAsync;
+};
+
+export const findExistingESLintConfiguration = async (
+    dependencies: FindExistingESLintConfigurationDependencies,
+): Promise<ResultWithDataStatus<ESLintConfiguration | string[]>> => {
+    const globResult = await dependencies.globAsync(".eslintrc.{js,json,yaml}");
+    const packageContent = await fsFileSystem.readFile("package.json");
+    if (!(globResult instanceof Error)) {
+        return {
+            data: globResult,
+            status: ResultStatus.Succeeded,
+        };
+    }
+    if (globResult instanceof Error && packageContent instanceof Error) {
+        return {
+            errors: [globResult, packageContent],
+            status: ResultStatus.Failed,
+        };
+    }
+    if (globResult instanceof Error && typeof packageContent === "string") {
+        const parsedPackage: Record<string, unknown> = JSON.parse(packageContent);
+        if (parsedPackage.hasOwnProperty("eslintConfig")) {
+            return {
+                data: parsedPackage.eslintConfig as ESLintConfiguration,
+                status: ResultStatus.Succeeded,
+            };
+        }
+    }
+    return {
+        errors: [new Error("Could not find an existing ESLint Config")],
+        status: ResultStatus.Failed,
+    };
+};