diff --git a/scripts/build/gulp-typescript-oop/protocol.js b/scripts/build/gulp-typescript-oop/protocol.js
index 58e60b058d4..714b94f22a1 100644
--- a/scripts/build/gulp-typescript-oop/protocol.js
+++ b/scripts/build/gulp-typescript-oop/protocol.js
@@ -140,7 +140,7 @@ function diagnosticFromJson(json, host) {
         category: json.category,
         code: json.code,
         source: json.source,
-        relatedInformation: json.relatedInformation && json.relatedInformation.map(diagnosticRelatedInformationFromJson, host)
+        relatedInformation: json.relatedInformation && json.relatedInformation.map(json => diagnosticRelatedInformationFromJson(json, host))
     });
 }
 exports.diagnosticFromJson = diagnosticFromJson;
@@ -169,7 +169,9 @@ function diagnosticRelatedInformationFromJson(json, host) {
         file: json.file && sourceFileFromJson(json.file, host),
         start: json.start,
         length: json.length,
-        messageText: json.messageText
+        messageText: json.messageText,
+        category: json.category,
+        code: json.code
     };
 }
 exports.diagnosticRelatedInformationFromJson = diagnosticRelatedInformationFromJson;
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f2f6ad93562..d3974da9930 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13900,6 +13900,18 @@ namespace ts {
             return flow.id;
         }
 
+        function typeMaybeAssignableTo(source: Type, target: Type) {
+            if (!(source.flags & TypeFlags.Union)) {
+                return isTypeAssignableTo(source, target);
+            }
+            for (const t of (<UnionType>source).types) {
+                if (isTypeAssignableTo(t, target)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         // Remove those constituent types of declaredType to which no constituent type of assignedType is assignable.
         // For example, when a variable of type number | string | boolean is assigned a value of type number | boolean,
         // we remove type string.
@@ -13908,8 +13920,12 @@ namespace ts {
                 if (assignedType.flags & TypeFlags.Never) {
                     return assignedType;
                 }
-                const reducedType = filterType(declaredType, t => isTypeComparableTo(assignedType, t));
-                if (!(reducedType.flags & TypeFlags.Never)) {
+                const reducedType = filterType(declaredType, t => typeMaybeAssignableTo(assignedType, t));
+                // Our crude heuristic produces an invalid result in some cases: see GH#26130.
+                // For now, when that happens, we give up and don't narrow at all.  (This also
+                // means we'll never narrow for erroneous assignments where the assigned type
+                // is not assignable to the declared type.)
+                if (isTypeAssignableTo(assignedType, reducedType)) {
                     return reducedType;
                 }
             }
@@ -19442,11 +19458,13 @@ namespace ts {
             const callSignatures = getSignaturesOfType(expressionType, SignatureKind.Call);
             if (callSignatures.length) {
                 const signature = resolveCall(node, callSignatures, candidatesOutArray, isForSignatureHelp);
-                if (signature.declaration && !isJavascriptConstructor(signature.declaration) && getReturnTypeOfSignature(signature) !== voidType) {
-                    error(node, Diagnostics.Only_a_void_function_can_be_called_with_the_new_keyword);
-                }
-                if (getThisTypeOfSignature(signature) === voidType) {
-                    error(node, Diagnostics.A_function_that_is_called_with_the_new_keyword_cannot_have_a_this_type_that_is_void);
+                if (!noImplicitAny) {
+                    if (signature.declaration && !isJavascriptConstructor(signature.declaration) && getReturnTypeOfSignature(signature) !== voidType) {
+                        error(node, Diagnostics.Only_a_void_function_can_be_called_with_the_new_keyword);
+                    }
+                    if (getThisTypeOfSignature(signature) === voidType) {
+                        error(node, Diagnostics.A_function_that_is_called_with_the_new_keyword_cannot_have_a_this_type_that_is_void);
+                    }
                 }
                 return signature;
             }
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index badbfc4fa3f..613fe7f5c84 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -2593,14 +2593,14 @@ namespace ts {
         }
 
         function emitSyntheticTripleSlashReferencesIfNeeded(node: Bundle) {
-            emitTripleSlashDirectives(!!node.hasNoDefaultLib, node.syntheticFileReferences || [], node.syntheticTypeReferences || []);
+            emitTripleSlashDirectives(!!node.hasNoDefaultLib, node.syntheticFileReferences || [], node.syntheticTypeReferences || [], node.syntheticLibReferences || []);
         }
 
         function emitTripleSlashDirectivesIfNeeded(node: SourceFile) {
-            if (node.isDeclarationFile) emitTripleSlashDirectives(node.hasNoDefaultLib, node.referencedFiles, node.typeReferenceDirectives);
+            if (node.isDeclarationFile) emitTripleSlashDirectives(node.hasNoDefaultLib, node.referencedFiles, node.typeReferenceDirectives, node.libReferenceDirectives);
         }
 
-        function emitTripleSlashDirectives(hasNoDefaultLib: boolean, files: ReadonlyArray<FileReference>, types: ReadonlyArray<FileReference>) {
+        function emitTripleSlashDirectives(hasNoDefaultLib: boolean, files: ReadonlyArray<FileReference>, types: ReadonlyArray<FileReference>, libs: ReadonlyArray<FileReference>) {
             if (hasNoDefaultLib) {
                 write(`/// <reference no-default-lib="true"/>`);
                 writeLine();
@@ -2628,6 +2628,10 @@ namespace ts {
                 write(`/// <reference types="${directive.fileName}" />`);
                 writeLine();
             }
+            for (const directive of libs) {
+                write(`/// <reference lib="${directive.fileName}" />`);
+                writeLine();
+            }
         }
 
         function emitSourceFileWorker(node: SourceFile) {
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index d52025f5a30..abbc935cf65 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -1237,6 +1237,7 @@ namespace ts {
                 getSourceFile: program.getSourceFile,
                 getSourceFileByPath: program.getSourceFileByPath,
                 getSourceFiles: program.getSourceFiles,
+                getLibFileFromReference: program.getLibFileFromReference,
                 isSourceFileFromExternalLibrary,
                 writeFile: writeFileCallback || (
                     (fileName, data, writeByteOrderMark, onError, sourceFiles) => host.writeFile(fileName, data, writeByteOrderMark, onError, sourceFiles)),
diff --git a/src/compiler/transformers/declarations.ts b/src/compiler/transformers/declarations.ts
index 2fa093128bc..063b5f1cd1d 100644
--- a/src/compiler/transformers/declarations.ts
+++ b/src/compiler/transformers/declarations.ts
@@ -33,7 +33,7 @@ namespace ts {
         let needsScopeFixMarker = false;
         let resultHasScopeMarker = false;
         let enclosingDeclaration: Node;
-        let necessaryTypeRefernces: Map<true> | undefined;
+        let necessaryTypeReferences: Map<true> | undefined;
         let lateMarkedStatements: LateVisibilityPaintedStatement[] | undefined;
         let lateStatementReplacementMap: Map<VisitResult<LateVisibilityPaintedStatement>>;
         let suppressNewDiagnosticContexts: boolean;
@@ -53,6 +53,7 @@ namespace ts {
 
         let currentSourceFile: SourceFile;
         let refs: Map<SourceFile>;
+        let libs: Map<boolean>;
         const resolver = context.getEmitResolver();
         const options = context.getCompilerOptions();
         const newLine = getNewLineCharacter(options);
@@ -63,9 +64,9 @@ namespace ts {
             if (!typeReferenceDirectives) {
                 return;
             }
-            necessaryTypeRefernces = necessaryTypeRefernces || createMap<true>();
+            necessaryTypeReferences = necessaryTypeReferences || createMap<true>();
             for (const ref of typeReferenceDirectives) {
-                necessaryTypeRefernces.set(ref, true);
+                necessaryTypeReferences.set(ref, true);
             }
         }
 
@@ -163,6 +164,7 @@ namespace ts {
             if (node.kind === SyntaxKind.Bundle) {
                 isBundledEmit = true;
                 refs = createMap<SourceFile>();
+                libs = createMap<boolean>();
                 let hasNoDefaultLib = false;
                 const bundle = createBundle(map(node.sourceFiles,
                     sourceFile => {
@@ -177,6 +179,7 @@ namespace ts {
                         needsScopeFixMarker = false;
                         resultHasScopeMarker = false;
                         collectReferences(sourceFile, refs);
+                        collectLibs(sourceFile, libs);
                         if (isExternalModule(sourceFile)) {
                             resultHasExternalModuleIndicator = false; // unused in external module bundle emit (all external modules are within module blocks, therefore are known to be modules)
                             needsDeclare = false;
@@ -200,6 +203,7 @@ namespace ts {
                 }));
                 bundle.syntheticFileReferences = [];
                 bundle.syntheticTypeReferences = getFileReferencesForUsedTypeReferences();
+                bundle.syntheticLibReferences = getLibReferences();
                 bundle.hasNoDefaultLib = hasNoDefaultLib;
                 const outputFilePath = getDirectoryPath(normalizeSlashes(getOutputPathsFor(node, host, /*forceDtsPaths*/ true).declarationFilePath!));
                 const referenceVisitor = mapReferencesIntoArray(bundle.syntheticFileReferences as FileReference[], outputFilePath);
@@ -219,8 +223,9 @@ namespace ts {
             suppressNewDiagnosticContexts = false;
             lateMarkedStatements = undefined;
             lateStatementReplacementMap = createMap();
-            necessaryTypeRefernces = undefined;
+            necessaryTypeReferences = undefined;
             refs = collectReferences(currentSourceFile, createMap());
+            libs = collectLibs(currentSourceFile, createMap());
             const references: FileReference[] = [];
             const outputFilePath = getDirectoryPath(normalizeSlashes(getOutputPathsFor(node, host, /*forceDtsPaths*/ true).declarationFilePath!));
             const referenceVisitor = mapReferencesIntoArray(references, outputFilePath);
@@ -231,12 +236,16 @@ namespace ts {
             if (isExternalModule(node) && (!resultHasExternalModuleIndicator || (needsScopeFixMarker && !resultHasScopeMarker))) {
                 combinedStatements = setTextRange(createNodeArray([...combinedStatements, createExportDeclaration(/*decorators*/ undefined, /*modifiers*/ undefined, createNamedExports([]), /*moduleSpecifier*/ undefined)]), combinedStatements);
             }
-            const updated = updateSourceFileNode(node, combinedStatements, /*isDeclarationFile*/ true, references, getFileReferencesForUsedTypeReferences(), node.hasNoDefaultLib);
+            const updated = updateSourceFileNode(node, combinedStatements, /*isDeclarationFile*/ true, references, getFileReferencesForUsedTypeReferences(), node.hasNoDefaultLib, getLibReferences());
             updated.exportedModulesFromDeclarationEmit = exportedModulesFromDeclarationEmit;
             return updated;
 
+            function getLibReferences() {
+                return map(arrayFrom(libs.keys()), lib => ({ fileName: lib, pos: -1, end: -1 }));
+            }
+
             function getFileReferencesForUsedTypeReferences() {
-                return necessaryTypeRefernces ? mapDefined(arrayFrom(necessaryTypeRefernces.keys()), getFileReferenceForTypeName) : [];
+                return necessaryTypeReferences ? mapDefined(arrayFrom(necessaryTypeReferences.keys()), getFileReferenceForTypeName) : [];
             }
 
             function getFileReferenceForTypeName(typeName: string): FileReference | undefined {
@@ -297,6 +306,16 @@ namespace ts {
             return ret;
         }
 
+        function collectLibs(sourceFile: SourceFile, ret: Map<boolean>) {
+            forEach(sourceFile.libReferenceDirectives, ref => {
+                const lib = host.getLibFileFromReference(ref);
+                if (lib) {
+                    ret.set(ref.fileName.toLocaleLowerCase(), true);
+                }
+            });
+            return ret;
+        }
+
         function filterBindingPatternInitializers(name: BindingName) {
             if (name.kind === SyntaxKind.Identifier) {
                 return name;
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 8696512071d..4330a776d04 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -2648,6 +2648,7 @@ namespace ts {
         sourceFiles: ReadonlyArray<SourceFile>;
         /* @internal */ syntheticFileReferences?: ReadonlyArray<FileReference>;
         /* @internal */ syntheticTypeReferences?: ReadonlyArray<FileReference>;
+        /* @internal */ syntheticLibReferences?: ReadonlyArray<FileReference>;
         /* @internal */ hasNoDefaultLib?: boolean;
     }
 
@@ -5074,6 +5075,7 @@ namespace ts {
 
         /* @internal */
         isSourceFileFromExternalLibrary(file: SourceFile): boolean;
+        getLibFileFromReference(ref: FileReference): SourceFile | undefined;
 
         getCommonSourceDirectory(): string;
         getCanonicalFileName(fileName: string): string;
diff --git a/src/services/documentRegistry.ts b/src/services/documentRegistry.ts
index ee99aed930c..7a21cebb4f3 100644
--- a/src/services/documentRegistry.ts
+++ b/src/services/documentRegistry.ts
@@ -184,7 +184,7 @@ namespace ts {
 
             const bucket = getBucketForCompilationSettings(key, /*createIfMissing*/ true);
             let entry = bucket.get(path);
-            const scriptTarget = scriptKind === ScriptKind.JSON ? ScriptTarget.JSON : compilationSettings.target;
+            const scriptTarget = scriptKind === ScriptKind.JSON ? ScriptTarget.JSON : compilationSettings.target || ScriptTarget.ES5;
             if (!entry && externalCache) {
                 const sourceFile = externalCache.getDocument(key, path);
                 if (sourceFile) {
@@ -199,7 +199,7 @@ namespace ts {
 
             if (!entry) {
                 // Have never seen this file with these settings.  Create a new source file for it.
-                const sourceFile = createLanguageServiceSourceFile(fileName, scriptSnapshot, scriptTarget!, version, /*setNodeParents*/ false, scriptKind); // TODO: GH#18217
+                const sourceFile = createLanguageServiceSourceFile(fileName, scriptSnapshot, scriptTarget, version, /*setNodeParents*/ false, scriptKind);
                 if (externalCache) {
                     externalCache.setDocument(key, path, sourceFile);
                 }
diff --git a/src/testRunner/unittests/convertToAsyncFunction.ts b/src/testRunner/unittests/convertToAsyncFunction.ts
index 3b400fd0c2a..f39b8080ed2 100644
--- a/src/testRunner/unittests/convertToAsyncFunction.ts
+++ b/src/testRunner/unittests/convertToAsyncFunction.ts
@@ -319,38 +319,6 @@ interface String { charAt: any; }
 interface Array<T> {}`
     };
 
-    const newLineCharacter = "\n";
-    const formatOptions: FormatCodeSettings = {
-        indentSize: 4,
-        tabSize: 4,
-        newLineCharacter,
-        convertTabsToSpaces: true,
-        indentStyle: IndentStyle.Smart,
-        insertSpaceAfterConstructor: false,
-        insertSpaceAfterCommaDelimiter: true,
-        insertSpaceAfterSemicolonInForStatements: true,
-        insertSpaceBeforeAndAfterBinaryOperators: true,
-        insertSpaceAfterKeywordsInControlFlowStatements: true,
-        insertSpaceAfterFunctionKeywordForAnonymousFunctions: false,
-        insertSpaceAfterOpeningAndBeforeClosingNonemptyParenthesis: false,
-        insertSpaceAfterOpeningAndBeforeClosingNonemptyBrackets: false,
-        insertSpaceAfterOpeningAndBeforeClosingNonemptyBraces: true,
-        insertSpaceAfterOpeningAndBeforeClosingTemplateStringBraces: false,
-        insertSpaceAfterOpeningAndBeforeClosingJsxExpressionBraces: false,
-        insertSpaceBeforeFunctionParenthesis: false,
-        placeOpenBraceOnNewLineForFunctions: false,
-        placeOpenBraceOnNewLineForControlBlocks: false,
-    };
-
-    const notImplementedHost: LanguageServiceHost = {
-        getCompilationSettings: notImplemented,
-        getScriptFileNames: notImplemented,
-        getScriptVersion: notImplemented,
-        getScriptSnapshot: notImplemented,
-        getDefaultLibFileName: notImplemented,
-        getCurrentDirectory: notImplemented,
-    };
-
     function testConvertToAsyncFunction(caption: string, text: string, baselineFolder: string, description: DiagnosticMessage, includeLib?: boolean) {
         const t = getTest(text);
         const selectionRange = t.ranges.get("selection")!;
@@ -389,7 +357,7 @@ interface Array<T> {}`
                 cancellationToken: { throwIfCancellationRequested: noop, isCancellationRequested: returnFalse },
                 preferences: emptyOptions,
                 host: notImplementedHost,
-                formatContext: formatting.getFormatContext(formatOptions)
+                formatContext: formatting.getFormatContext(testFormatOptions)
             };
 
             const diagnostics = languageService.getSuggestionDiagnostics(f.path);
diff --git a/src/testRunner/unittests/extractTestHelpers.ts b/src/testRunner/unittests/extractTestHelpers.ts
index 1b3d00362ec..6e46c1304ab 100644
--- a/src/testRunner/unittests/extractTestHelpers.ts
+++ b/src/testRunner/unittests/extractTestHelpers.ts
@@ -86,7 +86,7 @@ namespace ts {
         placeOpenBraceOnNewLineForControlBlocks: false,
     };
 
-    const notImplementedHost: LanguageServiceHost = {
+    export const notImplementedHost: LanguageServiceHost = {
         getCompilationSettings: notImplemented,
         getScriptFileNames: notImplemented,
         getScriptVersion: notImplemented,
diff --git a/tests/baselines/reference/assignmentTypeNarrowing.js b/tests/baselines/reference/assignmentTypeNarrowing.js
index 4d6b911b88b..24a08539eb7 100644
--- a/tests/baselines/reference/assignmentTypeNarrowing.js
+++ b/tests/baselines/reference/assignmentTypeNarrowing.js
@@ -27,6 +27,12 @@ let a: string[];
 for (x of a) {
     x; // string
 }
+
+// Repro from #26405
+
+type AOrArrA<T> = T | T[];
+const arr: AOrArrA<{x?: "ok"}> = [{ x: "ok" }]; // weak type
+arr.push({ x: "ok" });
 
 
 //// [assignmentTypeNarrowing.js]
@@ -51,3 +57,5 @@ for (var _i = 0, a_1 = a; _i < a_1.length; _i++) {
     x = a_1[_i];
     x; // string
 }
+var arr = [{ x: "ok" }]; // weak type
+arr.push({ x: "ok" });
diff --git a/tests/baselines/reference/assignmentTypeNarrowing.symbols b/tests/baselines/reference/assignmentTypeNarrowing.symbols
index b9e8f3f136d..36a2cf44dae 100644
--- a/tests/baselines/reference/assignmentTypeNarrowing.symbols
+++ b/tests/baselines/reference/assignmentTypeNarrowing.symbols
@@ -62,3 +62,23 @@ for (x of a) {
 >x : Symbol(x, Decl(assignmentTypeNarrowing.ts, 0, 3))
 }
 
+// Repro from #26405
+
+type AOrArrA<T> = T | T[];
+>AOrArrA : Symbol(AOrArrA, Decl(assignmentTypeNarrowing.ts, 27, 1))
+>T : Symbol(T, Decl(assignmentTypeNarrowing.ts, 31, 13))
+>T : Symbol(T, Decl(assignmentTypeNarrowing.ts, 31, 13))
+>T : Symbol(T, Decl(assignmentTypeNarrowing.ts, 31, 13))
+
+const arr: AOrArrA<{x?: "ok"}> = [{ x: "ok" }]; // weak type
+>arr : Symbol(arr, Decl(assignmentTypeNarrowing.ts, 32, 5))
+>AOrArrA : Symbol(AOrArrA, Decl(assignmentTypeNarrowing.ts, 27, 1))
+>x : Symbol(x, Decl(assignmentTypeNarrowing.ts, 32, 20))
+>x : Symbol(x, Decl(assignmentTypeNarrowing.ts, 32, 35))
+
+arr.push({ x: "ok" });
+>arr.push : Symbol(Array.push, Decl(lib.es5.d.ts, --, --))
+>arr : Symbol(arr, Decl(assignmentTypeNarrowing.ts, 32, 5))
+>push : Symbol(Array.push, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(assignmentTypeNarrowing.ts, 33, 10))
+
diff --git a/tests/baselines/reference/assignmentTypeNarrowing.types b/tests/baselines/reference/assignmentTypeNarrowing.types
index 2e2e6ad44eb..15b71c259ae 100644
--- a/tests/baselines/reference/assignmentTypeNarrowing.types
+++ b/tests/baselines/reference/assignmentTypeNarrowing.types
@@ -96,3 +96,25 @@ for (x of a) {
 >x : string
 }
 
+// Repro from #26405
+
+type AOrArrA<T> = T | T[];
+>AOrArrA : AOrArrA<T>
+
+const arr: AOrArrA<{x?: "ok"}> = [{ x: "ok" }]; // weak type
+>arr : AOrArrA<{ x?: "ok"; }>
+>x : "ok"
+>[{ x: "ok" }] : { x: "ok"; }[]
+>{ x: "ok" } : { x: "ok"; }
+>x : "ok"
+>"ok" : "ok"
+
+arr.push({ x: "ok" });
+>arr.push({ x: "ok" }) : number
+>arr.push : (...items: { x?: "ok"; }[]) => number
+>arr : { x?: "ok"; }[]
+>push : (...items: { x?: "ok"; }[]) => number
+>{ x: "ok" } : { x: "ok"; }
+>x : "ok"
+>"ok" : "ok"
+
diff --git a/tests/baselines/reference/enumAssignmentCompat3.types b/tests/baselines/reference/enumAssignmentCompat3.types
index f2a693515e5..a152cd624df 100644
--- a/tests/baselines/reference/enumAssignmentCompat3.types
+++ b/tests/baselines/reference/enumAssignmentCompat3.types
@@ -252,9 +252,9 @@ abc = merged; // missing 'd'
 >merged : Merged.E
 
 merged = abc; // ok
->merged = abc : First.E.a | First.E.b
+>merged = abc : First.E
 >merged : Merged.E
->abc : First.E.a | First.E.b
+>abc : First.E
 
 abc = merged2; // ok
 >abc = merged2 : Merged2.E
diff --git a/tests/baselines/reference/libReferenceDeclarationEmit.js b/tests/baselines/reference/libReferenceDeclarationEmit.js
new file mode 100644
index 00000000000..83082c3ee98
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmit.js
@@ -0,0 +1,25 @@
+//// [tests/cases/conformance/declarationEmit/libReferenceDeclarationEmit.ts] ////
+
+//// [file1.ts]
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+
+//// [file2.ts]
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+
+//// [file1.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+//// [file2.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+
+
+//// [file1.d.ts]
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+//// [file2.d.ts]
+/// <reference lib="dom" />
+export {};
diff --git a/tests/baselines/reference/libReferenceDeclarationEmit.symbols b/tests/baselines/reference/libReferenceDeclarationEmit.symbols
new file mode 100644
index 00000000000..3753ee0b80d
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmit.symbols
@@ -0,0 +1,13 @@
+=== tests/cases/conformance/declarationEmit/file1.ts ===
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+>elem : Symbol(elem, Decl(file1.ts, 1, 20))
+>HTMLElement : Symbol(HTMLElement, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
+=== tests/cases/conformance/declarationEmit/file2.ts ===
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+>elem : Symbol(elem, Decl(file2.ts, 2, 13))
+>HTMLElement : Symbol(HTMLElement, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
diff --git a/tests/baselines/reference/libReferenceDeclarationEmit.types b/tests/baselines/reference/libReferenceDeclarationEmit.types
new file mode 100644
index 00000000000..34102b07321
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmit.types
@@ -0,0 +1,11 @@
+=== tests/cases/conformance/declarationEmit/file1.ts ===
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+>elem : HTMLElement
+
+=== tests/cases/conformance/declarationEmit/file2.ts ===
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+>elem : HTMLElement
+
diff --git a/tests/baselines/reference/libReferenceDeclarationEmitBundle.js b/tests/baselines/reference/libReferenceDeclarationEmitBundle.js
new file mode 100644
index 00000000000..03474372f87
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmitBundle.js
@@ -0,0 +1,30 @@
+//// [tests/cases/conformance/declarationEmit/libReferenceDeclarationEmitBundle.ts] ////
+
+//// [file1.ts]
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+
+//// [file2.ts]
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+
+//// [bundle.js]
+define("file1", ["require", "exports"], function (require, exports) {
+    "use strict";
+    Object.defineProperty(exports, "__esModule", { value: true });
+});
+define("file2", ["require", "exports"], function (require, exports) {
+    "use strict";
+    Object.defineProperty(exports, "__esModule", { value: true });
+});
+
+
+//// [bundle.d.ts]
+/// <reference lib="dom" />
+declare module "file1" {
+    export const elem: HTMLElement;
+}
+declare module "file2" {
+    export {};
+}
diff --git a/tests/baselines/reference/libReferenceDeclarationEmitBundle.symbols b/tests/baselines/reference/libReferenceDeclarationEmitBundle.symbols
new file mode 100644
index 00000000000..3753ee0b80d
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmitBundle.symbols
@@ -0,0 +1,13 @@
+=== tests/cases/conformance/declarationEmit/file1.ts ===
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+>elem : Symbol(elem, Decl(file1.ts, 1, 20))
+>HTMLElement : Symbol(HTMLElement, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
+=== tests/cases/conformance/declarationEmit/file2.ts ===
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+>elem : Symbol(elem, Decl(file2.ts, 2, 13))
+>HTMLElement : Symbol(HTMLElement, Decl(lib.dom.d.ts, --, --), Decl(lib.dom.d.ts, --, --))
+
diff --git a/tests/baselines/reference/libReferenceDeclarationEmitBundle.types b/tests/baselines/reference/libReferenceDeclarationEmitBundle.types
new file mode 100644
index 00000000000..34102b07321
--- /dev/null
+++ b/tests/baselines/reference/libReferenceDeclarationEmitBundle.types
@@ -0,0 +1,11 @@
+=== tests/cases/conformance/declarationEmit/file1.ts ===
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+>elem : HTMLElement
+
+=== tests/cases/conformance/declarationEmit/file2.ts ===
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
+>elem : HTMLElement
+
diff --git a/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.errors.txt b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.errors.txt
new file mode 100644
index 00000000000..3c131f4136f
--- /dev/null
+++ b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.errors.txt
@@ -0,0 +1,21 @@
+tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts(2,1): error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts(5,1): error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts(8,1): error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+
+
+==== tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts (3 errors) ====
+    function fnNumber(this: void): number { return 90; }
+    new fnNumber(); // Error
+    ~~~~~~~~~~~~~~
+!!! error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+    
+    function fnVoid(this: void): void {}
+    new fnVoid(); // Error
+    ~~~~~~~~~~~~
+!!! error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+    
+    function functionVoidNoThis(): void {}
+    new functionVoidNoThis(); // Error
+    ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS7009: 'new' expression, whose target lacks a construct signature, implicitly has an 'any' type.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.js b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.js
new file mode 100644
index 00000000000..935c2ba036f
--- /dev/null
+++ b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.js
@@ -0,0 +1,18 @@
+//// [newOperatorErrorCases_noImplicitAny.ts]
+function fnNumber(this: void): number { return 90; }
+new fnNumber(); // Error
+
+function fnVoid(this: void): void {}
+new fnVoid(); // Error
+
+function functionVoidNoThis(): void {}
+new functionVoidNoThis(); // Error
+
+
+//// [newOperatorErrorCases_noImplicitAny.js]
+function fnNumber() { return 90; }
+new fnNumber(); // Error
+function fnVoid() { }
+new fnVoid(); // Error
+function functionVoidNoThis() { }
+new functionVoidNoThis(); // Error
diff --git a/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.symbols b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.symbols
new file mode 100644
index 00000000000..dadb2379223
--- /dev/null
+++ b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.symbols
@@ -0,0 +1,21 @@
+=== tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts ===
+function fnNumber(this: void): number { return 90; }
+>fnNumber : Symbol(fnNumber, Decl(newOperatorErrorCases_noImplicitAny.ts, 0, 0))
+>this : Symbol(this, Decl(newOperatorErrorCases_noImplicitAny.ts, 0, 18))
+
+new fnNumber(); // Error
+>fnNumber : Symbol(fnNumber, Decl(newOperatorErrorCases_noImplicitAny.ts, 0, 0))
+
+function fnVoid(this: void): void {}
+>fnVoid : Symbol(fnVoid, Decl(newOperatorErrorCases_noImplicitAny.ts, 1, 15))
+>this : Symbol(this, Decl(newOperatorErrorCases_noImplicitAny.ts, 3, 16))
+
+new fnVoid(); // Error
+>fnVoid : Symbol(fnVoid, Decl(newOperatorErrorCases_noImplicitAny.ts, 1, 15))
+
+function functionVoidNoThis(): void {}
+>functionVoidNoThis : Symbol(functionVoidNoThis, Decl(newOperatorErrorCases_noImplicitAny.ts, 4, 13))
+
+new functionVoidNoThis(); // Error
+>functionVoidNoThis : Symbol(functionVoidNoThis, Decl(newOperatorErrorCases_noImplicitAny.ts, 4, 13))
+
diff --git a/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.types b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.types
new file mode 100644
index 00000000000..bd1d8082aae
--- /dev/null
+++ b/tests/baselines/reference/newOperatorErrorCases_noImplicitAny.types
@@ -0,0 +1,25 @@
+=== tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts ===
+function fnNumber(this: void): number { return 90; }
+>fnNumber : (this: void) => number
+>this : void
+>90 : 90
+
+new fnNumber(); // Error
+>new fnNumber() : any
+>fnNumber : (this: void) => number
+
+function fnVoid(this: void): void {}
+>fnVoid : (this: void) => void
+>this : void
+
+new fnVoid(); // Error
+>new fnVoid() : any
+>fnVoid : (this: void) => void
+
+function functionVoidNoThis(): void {}
+>functionVoidNoThis : () => void
+
+new functionVoidNoThis(); // Error
+>new functionVoidNoThis() : any
+>functionVoidNoThis : () => void
+
diff --git a/tests/baselines/reference/numericLiteralTypes3.types b/tests/baselines/reference/numericLiteralTypes3.types
index 3fede24475c..9748eaccfca 100644
--- a/tests/baselines/reference/numericLiteralTypes3.types
+++ b/tests/baselines/reference/numericLiteralTypes3.types
@@ -118,9 +118,9 @@ function f4(a: A, b: B, c: C, d: D) {
 >c : C
 
     d = d;
->d = d : 1 | 2
+>d = d : D
+>d : D
 >d : D
->d : 1 | 2
 }
 
 function f5(a: A, b: B, c: C, d: D) {
diff --git a/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmit.ts b/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmit.ts
new file mode 100644
index 00000000000..2afc4290776
--- /dev/null
+++ b/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmit.ts
@@ -0,0 +1,12 @@
+// @target: esnext
+// @module: commonjs
+// @lib: esnext
+// @declaration: true
+// @filename: file1.ts
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+
+// @filename: file2.ts
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
\ No newline at end of file
diff --git a/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmitBundle.ts b/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmitBundle.ts
new file mode 100644
index 00000000000..e379567d559
--- /dev/null
+++ b/tests/cases/conformance/declarationEmit/libReferenceDeclarationEmitBundle.ts
@@ -0,0 +1,13 @@
+// @target: esnext
+// @module: amd
+// @lib: esnext
+// @declaration: true
+// @outFile: bundle.js
+// @filename: file1.ts
+/// <reference lib="dom" />
+export declare const elem: HTMLElement;
+
+// @filename: file2.ts
+/// <reference lib="dom" />
+export {}
+declare const elem: HTMLElement;
\ No newline at end of file
diff --git a/tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts b/tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts
index 0e5e257635a..19d12a1b81a 100644
--- a/tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts
+++ b/tests/cases/conformance/expressions/assignmentOperator/assignmentTypeNarrowing.ts
@@ -26,3 +26,9 @@ let a: string[];
 for (x of a) {
     x; // string
 }
+
+// Repro from #26405
+
+type AOrArrA<T> = T | T[];
+const arr: AOrArrA<{x?: "ok"}> = [{ x: "ok" }]; // weak type
+arr.push({ x: "ok" });
diff --git a/tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts b/tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts
new file mode 100644
index 00000000000..9b3b2c091d6
--- /dev/null
+++ b/tests/cases/conformance/expressions/newOperator/newOperatorErrorCases_noImplicitAny.ts
@@ -0,0 +1,10 @@
+// @noImplicitAny: true
+
+function fnNumber(this: void): number { return 90; }
+new fnNumber(); // Error
+
+function fnVoid(this: void): void {}
+new fnVoid(); // Error
+
+function functionVoidNoThis(): void {}
+new functionVoidNoThis(); // Error