Merge branch 'stweedie-master'

Author: vvakame

lib/utils.ts

@@ -3,6 +3,8 @@ import * as ts from "typescript";
 import * as fs from "fs";
 import * as path from "path";
 
+const TSCONFIG_CACHE: { [filePath: string]: ts.ParsedCommandLine; } = {};
+
 export function createDefaultFormatCodeSettings(): ts.FormatCodeSettings {
 
     return {
@@ -49,6 +51,10 @@ export function readFilesFromTsconfig(configPath: string): string[] {
 }
 
 export function readTsconfig(configPath: string): ts.ParsedCommandLine {
+    if (TSCONFIG_CACHE[configPath]) {
+        return TSCONFIG_CACHE[configPath];
+    }
+
     // for `extends` support. It supported from TypeScript 2.1.1.
     // `& { readFile(path: string): string; }` is backword compat for TypeScript compiler 2.0.3 support.
     const host: ts.ParseConfigHost & { readFile(path: string): string; } = {
@@ -63,6 +69,8 @@ export function readTsconfig(configPath: string): ts.ParsedCommandLine {
         throw new Error(parsed.errors.map(e => e.messageText).join("\n"));
     }
 
+    TSCONFIG_CACHE[configPath] = parsed;
+
     return parsed;
 }