fix(50654): "Move to a new file" breaks the declaration of referenced variable

src/services/refactors/moveToNewFile.ts

@@ -133,7 +133,7 @@ namespace ts.refactor {
     ) {
         const checker = program.getTypeChecker();
         const prologueDirectives = takeWhile(oldFile.statements, isPrologueDirective);
-        if (!oldFile.externalModuleIndicator && !oldFile.commonJsModuleIndicator) {
+        if (oldFile.externalModuleIndicator === undefined && oldFile.commonJsModuleIndicator === undefined && usage.oldImportsNeededByNewFile.size() === 0) {
             deleteMovedStatements(oldFile, toMove.ranges, changes);
             return [...prologueDirectives, ...toMove.all];
         }
@@ -402,7 +402,13 @@ namespace ts.refactor {
         switch (name.kind) {
             case SyntaxKind.Identifier:
                 if (isUnused(name)) {
-                    changes.delete(sourceFile, name);
+                    if (varDecl.initializer && isRequireCall(varDecl.initializer, /*requireStringLiteralLikeArgument*/ true)) {
+                        changes.delete(sourceFile,
+                            isVariableDeclarationList(varDecl.parent) && length(varDecl.parent.declarations) === 1 ? varDecl.parent.parent : varDecl);
+                    }
+                    else {
+                        changes.delete(sourceFile, name);
+                    }
                 }
                 break;
             case SyntaxKind.ArrayBindingPattern:
@@ -641,10 +647,12 @@ namespace ts.refactor {
     }
 
     interface ReadonlySymbolSet {
+        size(): number;
         has(symbol: Symbol): boolean;
         forEach(cb: (symbol: Symbol) => void): void;
         forEachEntry<T>(cb: (symbol: Symbol) => T | undefined): T | undefined;
     }
+
     class SymbolSet implements ReadonlySymbolSet {
         private map = new Map<string, Symbol>();
         add(symbol: Symbol): void {
@@ -667,6 +675,9 @@ namespace ts.refactor {
             copyEntries(this.map, clone.map);
             return clone;
         }
+        size() {
+            return this.map.size;
+        }
     }
 
     type TopLevelExpressionStatement = ExpressionStatement & { expression: BinaryExpression & { left: PropertyAccessExpression } }; // 'exports.x = ...'
@@ -775,7 +786,8 @@ namespace ts.refactor {
         if (useEs6Exports) {
             return !isExpressionStatement(decl) && hasSyntacticModifier(decl, ModifierFlags.Export) || !!(name && sourceFile.symbol.exports?.has(name.escapedText));
         }
-        return getNamesToExportInCommonJS(decl).some(name => sourceFile.symbol.exports!.has(escapeLeadingUnderscores(name)));
+        return !!sourceFile.symbol && !!sourceFile.symbol.exports &&
+            getNamesToExportInCommonJS(decl).some(name => sourceFile.symbol.exports!.has(escapeLeadingUnderscores(name)));
     }
 
     function addExport(decl: TopLevelDeclarationStatement, useEs6Exports: boolean): readonly Statement[] | undefined {

tests/cases/fourslash/moveToNewFile_requireImport1.ts

@@ -0,0 +1,28 @@
+/// <reference path="fourslash.ts" />
+
+// @allowJs: true
+
+// @filename: /a.js
+////module.exports = 1;
+
+// @filename: /b.js
+////var a = require("./a");
+////[|function f() {
+////    a;
+////}|]
+
+verify.noErrors();
+
+verify.moveToNewFile({
+    newFileContents: {
+        "/b.js": "",
+
+        "/f.js":
+`var a = require("./a");
+
+function f() {
+    a;
+}
+`,
+    },
+});

tests/cases/fourslash/moveToNewFile_requireImport2.ts

@@ -0,0 +1,33 @@
+/// <reference path="fourslash.ts" />
+
+// @allowJs: true
+
+// @filename: /a.js
+////module.exports = 1;
+
+// @filename: /b.js
+////var a = require("./a"),
+////    b = require("./a"),
+////    c = require("./a");
+////[|function f() {
+////    b;
+////}|]
+
+verify.noErrors();
+
+verify.moveToNewFile({
+    newFileContents: {
+        "/b.js":
+`var a = require("./a"),
+    c = require("./a");
+`,
+
+        "/f.js":
+`var b = require("./a");
+
+function f() {
+    b;
+}
+`,
+    },
+});

tests/cases/fourslash/moveToNewFile_requireImport3.ts

@@ -0,0 +1,33 @@
+/// <reference path="fourslash.ts" />
+
+// @module: commonjs
+// @moduleResolution: node
+
+// @filename: /node.d.ts
+////declare var module: any;
+////declare var require: any;
+
+// @filename: /a.ts
+////module.exports = 1;
+
+// @filename: /b.ts
+////var a = require("./a");
+////[|function f() {
+////    a;
+////}|]
+
+verify.noErrors();
+
+verify.moveToNewFile({
+    newFileContents: {
+        "/b.ts": "",
+
+        "/f.ts":
+`var a = require("./a");
+
+function f() {
+    a;
+}
+`,
+    },
+});