diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 1a0aabd97fd..49434e80aba 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -1,5 +1,4 @@
 /// <reference path="utilities.ts"/>
-/// <reference path="moduleNameResolver.ts"/>
 /// <reference path="parser.ts"/>
 
 /* @internal */
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 72d2ca92af0..d0781097f39 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1,3 +1,4 @@
+/// <reference path="moduleNameResolver.ts"/>
 /// <reference path="binder.ts"/>
 
 /* @internal */
diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 3967a867014..9de92cce3a5 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1889,6 +1889,78 @@ namespace ts {
             : ((fileName) => fileName.toLowerCase());
     }
 
+    /**
+     * patternStrings contains both pattern strings (containing "*") and regular strings.
+     * Return an exact match if possible, or a pattern match, or undefined.
+     * (These are verified by verifyCompilerOptions to have 0 or 1 "*" characters.)
+     */
+    /* @internal */
+    export function matchPatternOrExact(patternStrings: string[], candidate: string): string | Pattern | undefined {
+        const patterns: Pattern[] = [];
+        for (const patternString of patternStrings) {
+            const pattern = tryParsePattern(patternString);
+            if (pattern) {
+                patterns.push(pattern);
+            }
+            else if (patternString === candidate) {
+                // pattern was matched as is - no need to search further
+                return patternString;
+            }
+        }
+
+        return findBestPatternMatch(patterns, _ => _, candidate);
+    }
+
+    /* @internal */
+    export function patternText({prefix, suffix}: Pattern): string {
+        return `${prefix}*${suffix}`;
+    }
+
+    /**
+     * Given that candidate matches pattern, returns the text matching the '*'.
+     * E.g.: matchedText(tryParsePattern("foo*baz"), "foobarbaz") === "bar"
+     */
+    /* @internal */
+    export function matchedText(pattern: Pattern, candidate: string): string {
+        Debug.assert(isPatternMatch(pattern, candidate));
+        return candidate.substr(pattern.prefix.length, candidate.length - pattern.suffix.length);
+    }
+
+    /** Return the object corresponding to the best pattern to match `candidate`. */
+    /* @internal */
+    export function findBestPatternMatch<T>(values: T[], getPattern: (value: T) => Pattern, candidate: string): T | undefined {
+        let matchedValue: T | undefined = undefined;
+        // use length of prefix as betterness criteria
+        let longestMatchPrefixLength = -1;
+
+        for (const v of values) {
+            const pattern = getPattern(v);
+            if (isPatternMatch(pattern, candidate) && pattern.prefix.length > longestMatchPrefixLength) {
+                longestMatchPrefixLength = pattern.prefix.length;
+                matchedValue = v;
+            }
+        }
+
+        return matchedValue;
+    }
+
+    function isPatternMatch({prefix, suffix}: Pattern, candidate: string) {
+        return candidate.length >= prefix.length + suffix.length &&
+            startsWith(candidate, prefix) &&
+            endsWith(candidate, suffix);
+    }
+
+    /* @internal */
+    export function tryParsePattern(pattern: string): Pattern | undefined {
+        // This should be verified outside of here and a proper error thrown.
+        Debug.assert(hasZeroOrOneAsteriskCharacter(pattern));
+        const indexOfStar = pattern.indexOf("*");
+        return indexOfStar === -1 ? undefined : {
+            prefix: pattern.substr(0, indexOfStar),
+            suffix: pattern.substr(indexOfStar + 1)
+        };
+    }
+
     export function positionIsSynthesized(pos: number): boolean {
         // This is a fast way of testing the following conditions:
         //  pos === undefined || pos === null || isNaN(pos) || pos < 0;
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 03de307f2f3..90742f30c16 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -13,6 +13,9 @@ namespace ts {
         _i        = 0x10000000,  // Use/preference flag for '_i'
     }
 
+    const id = (s: SourceFile) => s;
+    const nullTransformers: Transformer[] = [ctx => id];
+
     // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
     export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile, emitOnlyDtsFiles?: boolean): EmitResult {
         const delimiters = createDelimiterMap();
@@ -192,7 +195,7 @@ const _super = (function (geti, seti) {
         const emittedFilesList: string[] = compilerOptions.listEmittedFiles ? [] : undefined;
         const emitterDiagnostics = createDiagnosticCollection();
         const newLine = host.getNewLine();
-        const transformers = getTransformers(compilerOptions);
+        const transformers: Transformer[] = emitOnlyDtsFiles ? nullTransformers : getTransformers(compilerOptions);
         const writer = createTextWriter(newLine);
         const {
             write,
@@ -271,7 +274,9 @@ const _super = (function (geti, seti) {
         function emitFile(jsFilePath: string, sourceMapFilePath: string, declarationFilePath: string, sourceFiles: SourceFile[], isBundledEmit: boolean) {
             // Make sure not to write js file and source map file if any of them cannot be written
             if (!host.isEmitBlocked(jsFilePath) && !compilerOptions.noEmit) {
-                printFile(jsFilePath, sourceMapFilePath, sourceFiles, isBundledEmit);
+                if (!emitOnlyDtsFiles) {
+                    printFile(jsFilePath, sourceMapFilePath, sourceFiles, isBundledEmit);
+                }
             }
             else {
                 emitSkipped = true;
@@ -282,7 +287,9 @@ const _super = (function (geti, seti) {
             }
 
             if (!emitSkipped && emittedFilesList) {
-                emittedFilesList.push(jsFilePath);
+                if (!emitOnlyDtsFiles) {
+                    emittedFilesList.push(jsFilePath);
+                }
                 if (sourceMapFilePath) {
                     emittedFilesList.push(sourceMapFilePath);
                 }
diff --git a/src/compiler/moduleNameResolver.ts b/src/compiler/moduleNameResolver.ts
index 6068cf55a7a..ca702173e79 100644
--- a/src/compiler/moduleNameResolver.ts
+++ b/src/compiler/moduleNameResolver.ts
@@ -512,75 +512,6 @@ namespace ts {
         }
     }
 
-    /**
-     * patternStrings contains both pattern strings (containing "*") and regular strings.
-     * Return an exact match if possible, or a pattern match, or undefined.
-     * (These are verified by verifyCompilerOptions to have 0 or 1 "*" characters.)
-     */
-    function matchPatternOrExact(patternStrings: string[], candidate: string): string | Pattern | undefined {
-        const patterns: Pattern[] = [];
-        for (const patternString of patternStrings) {
-            const pattern = tryParsePattern(patternString);
-            if (pattern) {
-                patterns.push(pattern);
-            }
-            else if (patternString === candidate) {
-                // pattern was matched as is - no need to search further
-                return patternString;
-            }
-        }
-
-        return findBestPatternMatch(patterns, _ => _, candidate);
-    }
-
-    function patternText({prefix, suffix}: Pattern): string {
-        return `${prefix}*${suffix}`;
-    }
-
-    /**
-     * Given that candidate matches pattern, returns the text matching the '*'.
-     * E.g.: matchedText(tryParsePattern("foo*baz"), "foobarbaz") === "bar"
-     */
-    function matchedText(pattern: Pattern, candidate: string): string {
-        Debug.assert(isPatternMatch(pattern, candidate));
-        return candidate.substr(pattern.prefix.length, candidate.length - pattern.suffix.length);
-    }
-
-    /** Return the object corresponding to the best pattern to match `candidate`. */
-    /* @internal */
-    export function findBestPatternMatch<T>(values: T[], getPattern: (value: T) => Pattern, candidate: string): T | undefined {
-        let matchedValue: T | undefined = undefined;
-        // use length of prefix as betterness criteria
-        let longestMatchPrefixLength = -1;
-
-        for (const v of values) {
-            const pattern = getPattern(v);
-            if (isPatternMatch(pattern, candidate) && pattern.prefix.length > longestMatchPrefixLength) {
-                longestMatchPrefixLength = pattern.prefix.length;
-                matchedValue = v;
-            }
-        }
-
-        return matchedValue;
-    }
-
-    function isPatternMatch({prefix, suffix}: Pattern, candidate: string) {
-        return candidate.length >= prefix.length + suffix.length &&
-            startsWith(candidate, prefix) &&
-            endsWith(candidate, suffix);
-    }
-
-    /* @internal */
-    export function tryParsePattern(pattern: string): Pattern | undefined {
-        // This should be verified outside of here and a proper error thrown.
-        Debug.assert(hasZeroOrOneAsteriskCharacter(pattern));
-        const indexOfStar = pattern.indexOf("*");
-        return indexOfStar === -1 ? undefined : {
-            prefix: pattern.substr(0, indexOfStar),
-            suffix: pattern.substr(indexOfStar + 1)
-        };
-    }
-
     export function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost): ResolvedModuleWithFailedLookupLocations {
         const containingDirectory = getDirectoryPath(containingFile);
         const supportedExtensions = getSupportedExtensions(compilerOptions);
diff --git a/src/services/services.ts b/src/services/services.ts
index da8cb5e9c30..eb103cebb11 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -945,6 +945,8 @@ namespace ts {
         let program: Program;
         let lastProjectVersion: string;
 
+        let lastTypesRootVersion = 0;
+
         const useCaseSensitivefileNames = false;
         const cancellationToken = new CancellationTokenObject(host.getCancellationToken && host.getCancellationToken());
 
@@ -993,6 +995,13 @@ namespace ts {
                 }
             }
 
+            const typeRootsVersion = host.getTypeRootsVersion ? host.getTypeRootsVersion() : 0;
+            if (lastTypesRootVersion !== typeRootsVersion) {
+                log("TypeRoots version has changed; provide new program");
+                program = undefined;
+                lastTypesRootVersion = typeRootsVersion;
+            }
+
             // Get a fresh cache of the host information
             let hostCache = new HostCache(host, getCanonicalFileName);
 
diff --git a/src/services/types.ts b/src/services/types.ts
index a6fc92d5460..79bee8d1818 100644
--- a/src/services/types.ts
+++ b/src/services/types.ts
@@ -148,6 +148,11 @@ namespace ts {
         readFile?(path: string, encoding?: string): string;
         fileExists?(path: string): boolean;
 
+        /*
+         * LS host can optionally implement these methods to support automatic updating when new type libraries are installed
+         */
+        getTypeRootsVersion?(): number;
+ 
         /*
          * LS host can optionally implement this method if it wants to be completely in charge of module name resolution.
          * if implementation is omitted then language service will use built-in module resolution logic and get answers to
diff --git a/tests/baselines/reference/assignmentTypeNarrowing_BACKUP_22380.types b/tests/baselines/reference/assignmentTypeNarrowing_BACKUP_22380.types
deleted file mode 100644
index bb9805ca5ba..00000000000
--- a/tests/baselines/reference/assignmentTypeNarrowing_BACKUP_22380.types
+++ /dev/null
@@ -1,106 +0,0 @@
-=== tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts ===
-let x: string | number | boolean | RegExp;
->x : string | number | boolean | RegExp
->RegExp : RegExp
-
-x = "";
->x = "" : ""
->x : string | number | boolean | RegExp
->"" : ""
-
-x; // string
->x : string
-
-[x] = [true];
->[x] = [true] : [true]
->[x] : [string | number | boolean | RegExp]
->x : string | number | boolean | RegExp
->[true] : [true]
->true : true
-
-x; // boolean
->x : true
-
-[x = ""] = [1];
->[x = ""] = [1] : [number]
->[x = ""] : [string]
->x = "" : ""
->x : string | number | boolean | RegExp
->"" : ""
->[1] : [number]
->1 : 1
-
-x; // string | number
->x : string | number
-
-({x} = {x: true});
->({x} = {x: true}) : { x: true; }
->{x} = {x: true} : { x: true; }
->{x} : { x: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x: true; }
-<<<<<<< HEAD
->x : true
-=======
->x : boolean
->>>>>>> origin/master
->true : true
-
-x; // boolean
->x : true
-
-({y: x} = {y: 1});
->({y: x} = {y: 1}) : { y: 1; }
->{y: x} = {y: 1} : { y: 1; }
->{y: x} : { y: string | number | boolean | RegExp; }
->y : string | number | boolean | RegExp
->x : string | number | boolean | RegExp
->{y: 1} : { y: 1; }
->y : number
->1 : 1
-
-x; // number
->x : number
-
-({x = ""} = {x: true});
->({x = ""} = {x: true}) : { x?: true; }
->{x = ""} = {x: true} : { x?: true; }
->{x = ""} : { x?: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x?: true; }
-<<<<<<< HEAD
->x : true
-=======
->x : boolean
->>>>>>> origin/master
->true : true
-
-x; // string | boolean
->x : string | true
-
-({y: x = /a/} = {y: 1});
->({y: x = /a/} = {y: 1}) : { y?: number; }
->{y: x = /a/} = {y: 1} : { y?: number; }
->{y: x = /a/} : { y?: RegExp; }
->y : RegExp
->x = /a/ : RegExp
->x : string | number | boolean | RegExp
->/a/ : RegExp
->{y: 1} : { y?: number; }
->y : number
->1 : 1
-
-x; // number | RegExp
->x : number | RegExp
-
-let a: string[];
->a : string[]
-
-for (x of a) {
->x : string | number | boolean | RegExp
->a : string[]
-
-    x; // string
->x : string
-}
-
diff --git a/tests/baselines/reference/assignmentTypeNarrowing_BASE_22380.types b/tests/baselines/reference/assignmentTypeNarrowing_BASE_22380.types
deleted file mode 100644
index be99a31501d..00000000000
--- a/tests/baselines/reference/assignmentTypeNarrowing_BASE_22380.types
+++ /dev/null
@@ -1,98 +0,0 @@
-=== tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts ===
-let x: string | number | boolean | RegExp;
->x : string | number | boolean | RegExp
->RegExp : RegExp
-
-x = "";
->x = "" : string
->x : string | number | boolean | RegExp
->"" : string
-
-x; // string
->x : string
-
-[x] = [true];
->[x] = [true] : [boolean]
->[x] : [string | number | boolean | RegExp]
->x : string | number | boolean | RegExp
->[true] : [boolean]
->true : boolean
-
-x; // boolean
->x : boolean
-
-[x = ""] = [1];
->[x = ""] = [1] : [number]
->[x = ""] : [string]
->x = "" : string
->x : string | number | boolean | RegExp
->"" : string
->[1] : [number]
->1 : number
-
-x; // string | number
->x : string | number
-
-({x} = {x: true});
->({x} = {x: true}) : { x: boolean; }
->{x} = {x: true} : { x: boolean; }
->{x} : { x: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x: boolean; }
->x : boolean
->true : boolean
-
-x; // boolean
->x : boolean
-
-({y: x} = {y: 1});
->({y: x} = {y: 1}) : { y: number; }
->{y: x} = {y: 1} : { y: number; }
->{y: x} : { y: string | number | boolean | RegExp; }
->y : string | number | boolean | RegExp
->x : string | number | boolean | RegExp
->{y: 1} : { y: number; }
->y : number
->1 : number
-
-x; // number
->x : number
-
-({x = ""} = {x: true});
->({x = ""} = {x: true}) : { x?: boolean; }
->{x = ""} = {x: true} : { x?: boolean; }
->{x = ""} : { x?: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x?: boolean; }
->x : boolean
->true : boolean
-
-x; // string | boolean
->x : string | boolean
-
-({y: x = /a/} = {y: 1});
->({y: x = /a/} = {y: 1}) : { y?: number; }
->{y: x = /a/} = {y: 1} : { y?: number; }
->{y: x = /a/} : { y?: RegExp; }
->y : RegExp
->x = /a/ : RegExp
->x : string | number | boolean | RegExp
->/a/ : RegExp
->{y: 1} : { y?: number; }
->y : number
->1 : number
-
-x; // number | RegExp
->x : number | RegExp
-
-let a: string[];
->a : string[]
-
-for (x of a) {
->x : string | number | boolean | RegExp
->a : string[]
-
-    x; // string
->x : string
-}
-
diff --git a/tests/baselines/reference/assignmentTypeNarrowing_LOCAL_22380.types b/tests/baselines/reference/assignmentTypeNarrowing_LOCAL_22380.types
deleted file mode 100644
index f46b2a16c3b..00000000000
--- a/tests/baselines/reference/assignmentTypeNarrowing_LOCAL_22380.types
+++ /dev/null
@@ -1,98 +0,0 @@
-=== tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts ===
-let x: string | number | boolean | RegExp;
->x : string | number | boolean | RegExp
->RegExp : RegExp
-
-x = "";
->x = "" : string
->x : string | number | boolean | RegExp
->"" : string
-
-x; // string
->x : string
-
-[x] = [true];
->[x] = [true] : [true]
->[x] : [string | number | boolean | RegExp]
->x : string | number | boolean | RegExp
->[true] : [true]
->true : true
-
-x; // boolean
->x : true
-
-[x = ""] = [1];
->[x = ""] = [1] : [number]
->[x = ""] : [string]
->x = "" : string
->x : string | number | boolean | RegExp
->"" : string
->[1] : [number]
->1 : number
-
-x; // string | number
->x : string | number
-
-({x} = {x: true});
->({x} = {x: true}) : { x: true; }
->{x} = {x: true} : { x: true; }
->{x} : { x: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x: true; }
->x : true
->true : true
-
-x; // boolean
->x : true
-
-({y: x} = {y: 1});
->({y: x} = {y: 1}) : { y: number; }
->{y: x} = {y: 1} : { y: number; }
->{y: x} : { y: string | number | boolean | RegExp; }
->y : string | number | boolean | RegExp
->x : string | number | boolean | RegExp
->{y: 1} : { y: number; }
->y : number
->1 : number
-
-x; // number
->x : number
-
-({x = ""} = {x: true});
->({x = ""} = {x: true}) : { x?: true; }
->{x = ""} = {x: true} : { x?: true; }
->{x = ""} : { x?: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x?: true; }
->x : true
->true : true
-
-x; // string | boolean
->x : string | true
-
-({y: x = /a/} = {y: 1});
->({y: x = /a/} = {y: 1}) : { y?: number; }
->{y: x = /a/} = {y: 1} : { y?: number; }
->{y: x = /a/} : { y?: RegExp; }
->y : RegExp
->x = /a/ : RegExp
->x : string | number | boolean | RegExp
->/a/ : RegExp
->{y: 1} : { y?: number; }
->y : number
->1 : number
-
-x; // number | RegExp
->x : number | RegExp
-
-let a: string[];
->a : string[]
-
-for (x of a) {
->x : string | number | boolean | RegExp
->a : string[]
-
-    x; // string
->x : string
-}
-
diff --git a/tests/baselines/reference/assignmentTypeNarrowing_REMOTE_22380.types b/tests/baselines/reference/assignmentTypeNarrowing_REMOTE_22380.types
deleted file mode 100644
index 8c5fea315ce..00000000000
--- a/tests/baselines/reference/assignmentTypeNarrowing_REMOTE_22380.types
+++ /dev/null
@@ -1,98 +0,0 @@
-=== tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts ===
-let x: string | number | boolean | RegExp;
->x : string | number | boolean | RegExp
->RegExp : RegExp
-
-x = "";
->x = "" : ""
->x : string | number | boolean | RegExp
->"" : ""
-
-x; // string
->x : string
-
-[x] = [true];
->[x] = [true] : [true]
->[x] : [string | number | boolean | RegExp]
->x : string | number | boolean | RegExp
->[true] : [true]
->true : true
-
-x; // boolean
->x : true
-
-[x = ""] = [1];
->[x = ""] = [1] : [number]
->[x = ""] : [string]
->x = "" : ""
->x : string | number | boolean | RegExp
->"" : ""
->[1] : [number]
->1 : 1
-
-x; // string | number
->x : string | number
-
-({x} = {x: true});
->({x} = {x: true}) : { x: true; }
->{x} = {x: true} : { x: true; }
->{x} : { x: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x: true; }
->x : boolean
->true : true
-
-x; // boolean
->x : true
-
-({y: x} = {y: 1});
->({y: x} = {y: 1}) : { y: 1; }
->{y: x} = {y: 1} : { y: 1; }
->{y: x} : { y: string | number | boolean | RegExp; }
->y : string | number | boolean | RegExp
->x : string | number | boolean | RegExp
->{y: 1} : { y: 1; }
->y : number
->1 : 1
-
-x; // number
->x : number
-
-({x = ""} = {x: true});
->({x = ""} = {x: true}) : { x?: true; }
->{x = ""} = {x: true} : { x?: true; }
->{x = ""} : { x?: string | number | boolean | RegExp; }
->x : string | number | boolean | RegExp
->{x: true} : { x?: true; }
->x : boolean
->true : true
-
-x; // string | boolean
->x : string | true
-
-({y: x = /a/} = {y: 1});
->({y: x = /a/} = {y: 1}) : { y?: number; }
->{y: x = /a/} = {y: 1} : { y?: number; }
->{y: x = /a/} : { y?: RegExp; }
->y : RegExp
->x = /a/ : RegExp
->x : string | number | boolean | RegExp
->/a/ : RegExp
->{y: 1} : { y?: number; }
->y : number
->1 : 1
-
-x; // number | RegExp
->x : number | RegExp
-
-let a: string[];
->a : string[]
-
-for (x of a) {
->x : string | number | boolean | RegExp
->a : string[]
-
-    x; // string
->x : string
-}
-