Redo as noEraslingImportedNames

Author: andrewbranch

src/compiler/checker.ts

@@ -38081,7 +38081,7 @@ namespace ts {
                 }
 
                 const isDeclaredTypeOnly = isTypeOnlyImportOrExportDeclaration(node);
-                if ((compilerOptions.isolatedModules || compilerOptions.importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact)
+                if (compilerOptions.isolatedModules
                     && !isDeclaredTypeOnly
                     && !(node.flags & NodeFlags.Ambient)
                     && (!(target.flags & SymbolFlags.Value) || getTypeOnlyAliasDeclaration(symbol))) {
@@ -38092,10 +38092,10 @@ namespace ts {
                         case SyntaxKind.ImportClause:
                         case SyntaxKind.ImportSpecifier:
                         case SyntaxKind.ImportEqualsDeclaration: {
-                            if (compilerOptions.importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact) {
+                            if (compilerOptions.noErasingImportedNames) {
                                 const message = isType
-                                    ? Diagnostics._0_is_a_type_and_must_be_imported_with_a_type_only_import_when_importsNotUsedAsValues_is_set_to_preserve_exact
-                                    : Diagnostics._0_resolves_to_a_type_only_declaration_and_must_be_imported_with_a_type_only_import_when_importsNotUsedAsValues_is_set_to_preserve_exact;
+                                    ? Diagnostics._0_is_a_type_and_must_be_imported_with_a_type_only_import_when_noErasingImportedNames_and_isolatedModules_are_both_enabled
+                                    : Diagnostics._0_resolves_to_a_type_only_declaration_and_must_be_imported_with_a_type_only_import_when_noErasingImportedNames_and_isolatedModules_are_both_enabled;
                                 const name = idText(node.kind === SyntaxKind.ImportSpecifier ? node.propertyName || node.name : node.name!);
                                 addTypeOnlyDeclarationRelatedInfo(
                                     error(node, message, name),
@@ -38106,29 +38106,21 @@ namespace ts {
                             break;
                         }
                         case SyntaxKind.ExportSpecifier: {
-                            // Don't allow re-exporting an export that will be elided when `--isolatedModules` is set
-                            // or when `--importsNotUsedAsValues` is `preserve-exact`.
-                            if (compilerOptions.isolatedModules &&
-                                compilerOptions.importsNotUsedAsValues !== ImportsNotUsedAsValues.PreserveExact &&
-                                typeOnlyAlias && getSourceFileOfNode(typeOnlyAlias) === getSourceFileOfNode(node)) {
-                                // In `isolatedModules` alone, `import type { A } from './a'; export { A }` is allowed
-                                // because single-file analysis can determine that the export should be dropped.
-                                // `--importsNotUsedAsValues=preserv-exact` is stricter; it refuses to touch non-type-only
-                                // imports and exports, so `export { A }` is not allowed if 'A' is not emitted.
+                            // Don't allow re-exporting an export that will be elided when `--isolatedModules` is set.
+                            // The exception is that `import type { A } from './a'; export { A }` is allowed
+                            // because single-file analysis can determine that the export should be dropped.
+                            if (getSourceFileOfNode(typeOnlyAlias) !== getSourceFileOfNode(node)) {
+                                const message = isType
+                                    ? Diagnostics.Re_exporting_a_type_when_the_isolatedModules_flag_is_provided_requires_using_export_type
+                                    : Diagnostics._0_resolves_to_a_type_only_declaration_and_must_be_re_exported_with_a_type_only_re_export_when_isolatedModules_is_enabled;
+                                const name = idText(node.propertyName || node.name);
+                                addTypeOnlyDeclarationRelatedInfo(
+                                    error(node, message, name),
+                                    isType ? undefined : typeOnlyAlias,
+                                    name
+                                );
                                 return;
                             }
-                            const message =
-                                compilerOptions.isolatedModules && isType ? Diagnostics.Re_exporting_a_type_when_the_isolatedModules_flag_is_provided_requires_using_export_type :
-                                compilerOptions.isolatedModules && !isType ? Diagnostics._0_resolves_to_a_type_only_declaration_and_must_be_re_exported_with_a_type_only_re_export_when_isolatedModules_is_enabled :
-                                isType ? Diagnostics._0_is_a_type_and_must_be_re_exported_with_a_type_only_re_export_when_importsNotUsedAsValues_is_set_to_preserve_exact :
-                                Diagnostics._0_resolves_to_a_type_only_declaration_and_must_be_re_exported_with_a_type_only_re_export_when_importsNotUsedAsValues_is_set_to_preserve_exact;
-                            const name = idText(node.propertyName || node.name);
-                            addTypeOnlyDeclarationRelatedInfo(
-                                error(node, message, name),
-                                isType ? undefined : typeOnlyAlias,
-                                name
-                            );
-                            return;
                         }
                     }
                 }

src/compiler/commandLineParser.ts

@@ -539,7 +539,6 @@ namespace ts {
                 "remove": ImportsNotUsedAsValues.Remove,
                 "preserve": ImportsNotUsedAsValues.Preserve,
                 "error": ImportsNotUsedAsValues.Error,
-                "preserve-exact": ImportsNotUsedAsValues.PreserveExact,
             })),
             affectsEmit: true,
             affectsSemanticDiagnostics: true,
@@ -1085,6 +1084,13 @@ namespace ts {
             category: Diagnostics.Advanced_Options,
             description: Diagnostics.Emit_class_fields_with_Define_instead_of_Set,
         },
+        {
+            name: "noErasingImportedNames",
+            type: "boolean",
+            affectsEmit: true,
+            category: Diagnostics.Advanced_Options,
+            description: Diagnostics.Disable_the_removal_of_unused_imported_identifiers_from_the_JavaScript_output
+        },
 
         {
             name: "keyofStringsOnly",

src/compiler/diagnosticMessages.json

@@ -1364,26 +1364,22 @@
         "category": "Error",
         "code": 1433
     },
-    "'{0}' is a type and must be imported with a type-only import when 'importsNotUsedAsValues' is set to 'preserve-exact'.": {
+    "'{0}' is a type and must be imported with a type-only import when 'noErasingImportedNames' and 'isolatedModules' are both enabled.": {
         "category": "Error",
         "code": 1434
     },
-    "'{0}' is a type and must be re-exported with a type-only re-export when 'importsNotUsedAsValues' is set to 'preserve-exact'.": {
-        "category": "Error",
-        "code": 1435
-    },
-    "'{0}' resolves to a type-only declaration and must be imported with a type-only import when 'importsNotUsedAsValues' is set to 'preserve-exact'.": {
+    "'{0}' resolves to a type-only declaration and must be imported with a type-only import when 'noErasingImportedNames' and 'isolatedModules' are both enabled.": {
         "category": "Error",
         "code": 1436
     },
-    "'{0}' resolves to a type-only declaration and must be re-exported with a type-only re-export when 'importsNotUsedAsValues' is set to 'preserve-exact'.": {
-        "category": "Error",
-        "code": 1437
-    },
     "'{0}' resolves to a type-only declaration and must be re-exported with a type-only re-export when 'isolatedModules' is enabled.": {
         "category": "Error",
         "code": 1438
     },
+    "Disable the removal of unused imported identifiers from the JavaScript output.": {
+        "category": "Message",
+        "code": 1439
+    },
 
     "The types of '{0}' are incompatible between these types.": {
         "category": "Error",
@@ -3962,7 +3958,7 @@
         "category": "Error",
         "code": 5094
     },
-    "Option 'importsNotUsedAsValues' may be set to 'preserve-exact' only when 'module' is set to 'es2015' or later.": {
+    "Option 'noErasingImportedNames' may be enabled only when 'module' is set to 'es2015' or later.": {
         "category": "Error",
         "code": 5095
     },

src/compiler/program.ts

@@ -3295,8 +3295,8 @@ namespace ts {
                 }
             }
 
-            if (options.importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact && getEmitModuleKind(options) < ModuleKind.ES2015) {
-                createOptionValueDiagnostic("importsNotUsedAsValues", Diagnostics.Option_importsNotUsedAsValues_may_be_set_to_preserve_exact_only_when_module_is_set_to_es2015_or_later);
+            if (options.noErasingImportedNames && getEmitModuleKind(options) < ModuleKind.ES2015) {
+                createOptionValueDiagnostic("importsNotUsedAsValues", Diagnostics.Option_noErasingImportedNames_may_be_enabled_only_when_module_is_set_to_es2015_or_later);
             }
 
             // If the emit is enabled make sure that every output file is unique and not overwriting any of the input files

src/compiler/transformers/ts.ts

@@ -2803,7 +2803,7 @@ namespace ts {
         }
 
         /**
-         * Visits an import declaration, eliding it if it is not referenced and `importsNotUsedAsValues` is not 'preserve' or 'preserve-exact'.
+         * Visits an import declaration, eliding it if it is not referenced and `importsNotUsedAsValues` is not 'preserve' and `noErasingImportedNames` is not set.
          *
          * @param node The import declaration node.
          */
@@ -2821,8 +2821,8 @@ namespace ts {
             // Elide the declaration if the import clause was elided.
             const importClause = visitNode(node.importClause, visitImportClause, isImportClause);
             return importClause ||
+                compilerOptions.noErasingImportedNames ||
                 importsNotUsedAsValues === ImportsNotUsedAsValues.Preserve ||
-                importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact ||
                 importsNotUsedAsValues === ImportsNotUsedAsValues.Error
                 ? factory.updateImportDeclaration(
                     node,
@@ -2834,13 +2834,13 @@ namespace ts {
         }
 
         /**
-         * Visits an import clause, eliding it if it is not referenced and `importsNotUsedAsValues` is not 'preserve-exact'.
+         * Visits an import clause, eliding it if it is not referenced and `noErasingImportedNames` is not set.
          *
          * @param node The import clause node.
          */
         function visitImportClause(node: ImportClause): VisitResult<ImportClause> {
             Debug.assert(!node.isTypeOnly);
-            if (importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact) {
+            if (compilerOptions.noErasingImportedNames) {
                 return node;
             }
             // Elide the import clause if we elide both its name and its named bindings.
@@ -2891,7 +2891,7 @@ namespace ts {
 
         /**
          * Visits an export declaration, eliding it if it does not contain a clause that resolves
-         * to a value and if `importsNotUsedAsValues` is not 'preserve-exact'.
+         * to a value and if `noErasingImportedNames` is not set.
          *
          * @param node The export declaration node.
          */
@@ -2900,7 +2900,7 @@ namespace ts {
                 return undefined;
             }
 
-            if (!node.exportClause || isNamespaceExport(node.exportClause) || importsNotUsedAsValues === ImportsNotUsedAsValues.PreserveExact) {
+            if (!node.exportClause || isNamespaceExport(node.exportClause) || compilerOptions.noErasingImportedNames) {
                 // never elide `export <whatever> from <whereever>` declarations -
                 // they should be kept for sideffects/untyped exports, even when the
                 // type checker doesn't know about any exports

src/compiler/types.ts

@@ -5954,6 +5954,7 @@ namespace ts {
         /*@internal*/noEmitForJsFiles?: boolean;
         noEmitHelpers?: boolean;
         noEmitOnError?: boolean;
+        noErasingImportedNames?: boolean;
         noErrorTruncation?: boolean;
         noFallthroughCasesInSwitch?: boolean;
         noImplicitAny?: boolean;  // Always combine with strict property
@@ -6071,7 +6072,6 @@ namespace ts {
         Remove,
         Preserve,
         Error,
-        PreserveExact,
     }
 
     export const enum NewLineKind {

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2850,6 +2850,7 @@ declare namespace ts {
         noEmit?: boolean;
         noEmitHelpers?: boolean;
         noEmitOnError?: boolean;
+        noErasingImportedNames?: boolean;
         noErrorTruncation?: boolean;
         noFallthroughCasesInSwitch?: boolean;
         noImplicitAny?: boolean;
@@ -2946,8 +2947,7 @@ declare namespace ts {
     export enum ImportsNotUsedAsValues {
         Remove = 0,
         Preserve = 1,
-        Error = 2,
-        PreserveExact = 3
+        Error = 2
     }
     export enum NewLineKind {
         CarriageReturnLineFeed = 0,

tests/baselines/reference/api/typescript.d.ts

@@ -2850,6 +2850,7 @@ declare namespace ts {
         noEmit?: boolean;
         noEmitHelpers?: boolean;
         noEmitOnError?: boolean;
+        noErasingImportedNames?: boolean;
         noErrorTruncation?: boolean;
         noFallthroughCasesInSwitch?: boolean;
         noImplicitAny?: boolean;
@@ -2946,8 +2947,7 @@ declare namespace ts {
     export enum ImportsNotUsedAsValues {
         Remove = 0,
         Preserve = 1,
-        Error = 2,
-        PreserveExact = 3
+        Error = 2
     }
     export enum NewLineKind {
         CarriageReturnLineFeed = 0,