From bf15eac16e11a80b2b73c8d8e818fedd29d6ef5b Mon Sep 17 00:00:00 2001
From: Josh Goldberg <me@joshuakgoldberg.com>
Date: Mon, 9 Mar 2020 16:53:49 -0400
Subject: [PATCH] Removed unused host variable in createProgramHost (#37278)

As stated in 26417, `host` is only ever written to and never read from. `createProgramHost` is the only place I could find that provides a member for `ProgramHost`'s `onCachedDirectoryStructureHostCreate`, so that's removed as well.
---
 src/compiler/watch.ts       | 5 -----
 src/compiler/watchPublic.ts | 4 ----
 2 files changed, 9 deletions(-)

diff --git a/src/compiler/watch.ts b/src/compiler/watch.ts
index 16c72126092..2eb32e24052 100644
--- a/src/compiler/watch.ts
+++ b/src/compiler/watch.ts
@@ -358,10 +358,6 @@ namespace ts {
      */
     export function createProgramHost<T extends BuilderProgram = EmitAndSemanticDiagnosticsBuilderProgram>(system: System, createProgram: CreateProgram<T> | undefined): ProgramHost<T> {
         const getDefaultLibLocation = memoize(() => getDirectoryPath(normalizePath(system.getExecutingFilePath())));
-        let host: DirectoryStructureHost = system;
-        // TODO: `host` is unused!
-        // eslint-disable-next-line @typescript-eslint/no-unused-expressions
-        host;
         return {
             useCaseSensitiveFileNames: () => system.useCaseSensitiveFileNames,
             getNewLine: () => system.newLine,
@@ -378,7 +374,6 @@ namespace ts {
             trace: s => system.write(s + system.newLine),
             createDirectory: path => system.createDirectory(path),
             writeFile: (path, data, writeByteOrderMark) => system.writeFile(path, data, writeByteOrderMark),
-            onCachedDirectoryStructureHostCreate: cacheHost => host = cacheHost || system,
             createHash: maybeBind(system, system.createHash),
             createProgram: createProgram || createEmitAndSemanticDiagnosticsBuilderProgram as any as CreateProgram<T>
         };
diff --git a/src/compiler/watchPublic.ts b/src/compiler/watchPublic.ts
index 5c0375030c3..21464f6929f 100644
--- a/src/compiler/watchPublic.ts
+++ b/src/compiler/watchPublic.ts
@@ -111,7 +111,6 @@ namespace ts {
         // TODO: GH#18217 Optional methods are frequently asserted
         createDirectory?(path: string): void;
         writeFile?(path: string, data: string, writeByteOrderMark?: boolean): void;
-        onCachedDirectoryStructureHostCreate?(host: CachedDirectoryStructureHost): void;
     }
 
     export interface WatchCompilerHost<T extends BuilderProgram> extends ProgramHost<T>, WatchHost {
@@ -247,9 +246,6 @@ namespace ts {
         let hasChangedConfigFileParsingErrors = false;
 
         const cachedDirectoryStructureHost = configFileName === undefined ? undefined : createCachedDirectoryStructureHost(host, currentDirectory, useCaseSensitiveFileNames);
-        if (cachedDirectoryStructureHost && host.onCachedDirectoryStructureHostCreate) {
-            host.onCachedDirectoryStructureHostCreate(cachedDirectoryStructureHost);
-        }
         const directoryStructureHost: DirectoryStructureHost = cachedDirectoryStructureHost || host;
         const parseConfigFileHost = parseConfigHostFromCompilerHostLike(host, directoryStructureHost);