Don’t use 'import =' for auto-import when esModuleInterop is on unless it’s already been done (#36475)

* Revisit esModuleInterop import kind priority yet again

* Test was wholly redundant

* Check for precedent is simpler now

Author: andrewbranch

src/services/codefixes/importFixes.ts

@@ -461,28 +461,32 @@ namespace ts.codefix {
         const defaultExport = checker.tryGetMemberInModuleExports(InternalSymbolName.Default, moduleSymbol);
         if (defaultExport) return { symbol: defaultExport, kind: ImportKind.Default };
         const exportEquals = checker.resolveExternalModuleSymbol(moduleSymbol);
-        return exportEquals === moduleSymbol ? undefined : { symbol: exportEquals, kind: getExportEqualsImportKind(importingFile, compilerOptions, checker) };
+        return exportEquals === moduleSymbol ? undefined : { symbol: exportEquals, kind: getExportEqualsImportKind(importingFile, compilerOptions) };
     }
 
-    function getExportEqualsImportKind(importingFile: SourceFile, compilerOptions: CompilerOptions, checker: TypeChecker): ImportKind {
+    function getExportEqualsImportKind(importingFile: SourceFile, compilerOptions: CompilerOptions): ImportKind {
+        const allowSyntheticDefaults = getAllowSyntheticDefaultImports(compilerOptions);
+        // 1. 'import =' will not work in es2015+, so the decision is between a default
+        //    and a namespace import, based on allowSyntheticDefaultImports/esModuleInterop.
         if (getEmitModuleKind(compilerOptions) >= ModuleKind.ES2015) {
-            return getAllowSyntheticDefaultImports(compilerOptions) ? ImportKind.Default : ImportKind.Namespace;
+            return allowSyntheticDefaults ? ImportKind.Default : ImportKind.Namespace;
         }
+        // 2. 'import =' will not work in JavaScript, so the decision is between a default
+        //    and const/require.
         if (isInJSFile(importingFile)) {
             return isExternalModule(importingFile) ? ImportKind.Default : ImportKind.ConstEquals;
         }
+        // 3. At this point the most correct choice is probably 'import =', but people
+        //    really hate that, so look to see if the importing file has any precedent
+        //    on how to handle it.
         for (const statement of importingFile.statements) {
             if (isImportEqualsDeclaration(statement)) {
                 return ImportKind.Equals;
             }
-            if (isImportDeclaration(statement) && statement.importClause && statement.importClause.name) {
-                const moduleSymbol = checker.getImmediateAliasedSymbol(statement.importClause.symbol);
-                if (moduleSymbol && moduleSymbol.name !== InternalSymbolName.Default) {
-                    return ImportKind.Default;
-                }
-            }
         }
-        return ImportKind.Equals;
+        // 4. We have no precedent to go on, so just use a default import if
+        //    allowSyntheticDefaultImports/esModuleInterop is enabled.
+        return allowSyntheticDefaults ? ImportKind.Default : ImportKind.Equals;
     }
 
     function getDefaultExportInfoWorker(defaultExport: Symbol, moduleSymbol: Symbol, checker: TypeChecker, compilerOptions: CompilerOptions): { readonly symbolForMeaning: Symbol, readonly name: string } | undefined {

tests/cases/fourslash/importNameCodeFixNewImportExportEqualsCommonJSInteropOn.ts

@@ -18,7 +18,7 @@
 ////}
 
 // @Filename: /a.ts
-////import bar from "bar";
+////import bar = require("bar");
 ////
 ////foo
 
@@ -27,25 +27,27 @@
 
 // @Filename: /c.ts
 ////import es from "es";
+////import bar = require("bar");
 ////
 ////foo
 
 // 1. Should match existing imports of 'export ='
 goTo.file('/a.ts');
-verify.importFixAtPosition([`import bar from "bar";
-import foo from "foo";
+verify.importFixAtPosition([`import bar = require("bar");
+import foo = require("foo");
 
 foo`]);
 
-// 2. Should default to ImportEquals
+// 2. Should default to default import
 goTo.file('/b.ts');
-verify.importFixAtPosition([`import foo = require("foo");
+verify.importFixAtPosition([`import foo from "foo";
 
 foo`]);
 
 // 3. Importing an 'export default' doesn’t count toward the usage heursitic
 goTo.file('/c.ts');
 verify.importFixAtPosition([`import es from "es";
+import bar = require("bar");
 import foo = require("foo");
 
 foo`]);