Fix: debug and implement correct diagnostic logic for unsafe import rewrites

The diagnostic for error TS2876 was not being triggered because the rewrite check logic was placed outside the `errorNode != nil` block. Moving it inside the error handling block and fixing the conditional logic now correctly detects when a module specifier looks like a file name but resolves to a different location, triggering the appropriate "unsafe to rewrite" error.

Co-authored-by: andrewbranch <3277153+andrewbranch@users.noreply.github.com>

Author: Copilot

internal/checker/checker.go

@@ -14497,35 +14497,35 @@ func (c *Checker) resolveExternalModule(location *ast.Node, moduleReference stri
 						tsExtension,
 					)
 				}
+			} else if c.compilerOptions.RewriteRelativeImportExtensions.IsTrue() &&
+				location.Flags&ast.NodeFlagsAmbient == 0 &&
+				!tspath.IsDeclarationFileName(moduleReference) &&
+				!ast.IsLiteralImportTypeNode(location) &&
+				!ast.IsPartOfTypeOnlyImportOrExportDeclaration(location) {
+				shouldRewrite := c.shouldRewriteModuleSpecifier(moduleReference)
+				if !resolvedModule.ResolvedUsingTsExtension && shouldRewrite {
+					relativeToSourceFile := tspath.GetRelativePathFromDirectory(
+						tspath.GetDirectoryPath(tspath.GetNormalizedAbsolutePath(importingSourceFile.FileName(), c.program.GetCurrentDirectory())),
+						resolvedModule.ResolvedFileName,
+						tspath.ComparePathsOptions{
+							UseCaseSensitiveFileNames: c.program.UseCaseSensitiveFileNames(),
+							CurrentDirectory:          c.program.GetCurrentDirectory(),
+						},
+					)
+					c.error(
+						errorNode,
+						diagnostics.This_relative_import_path_is_unsafe_to_rewrite_because_it_looks_like_a_file_name_but_actually_resolves_to_0,
+						relativeToSourceFile,
+					)
+				} else if resolvedModule.ResolvedUsingTsExtension && !shouldRewrite && c.sourceFileMayBeEmitted(sourceFile) {
+					c.error(
+						errorNode,
+						diagnostics.This_import_uses_a_0_extension_to_resolve_to_an_input_TypeScript_file_but_will_not_be_rewritten_during_emit_because_it_is_not_a_relative_path,
+						tspath.GetAnyExtensionFromPath(moduleReference, nil, false),
+					)
+				}
+				// TODO: Add project reference check when GetResolvedProjectReferenceToRedirect is implemented
 			}
-		} else if c.compilerOptions.RewriteRelativeImportExtensions.IsTrue() &&
-			location.Flags&ast.NodeFlagsAmbient == 0 &&
-			!tspath.IsDeclarationFileName(moduleReference) &&
-			!ast.IsLiteralImportTypeNode(location) &&
-			!ast.IsPartOfTypeOnlyImportOrExportDeclaration(location) {
-			shouldRewrite := c.shouldRewriteModuleSpecifier(moduleReference)
-			if !resolvedModule.ResolvedUsingTsExtension && shouldRewrite {
-				relativeToSourceFile := tspath.GetRelativePathFromDirectory(
-					tspath.GetDirectoryPath(tspath.GetNormalizedAbsolutePath(importingSourceFile.FileName(), c.program.GetCurrentDirectory())),
-					resolvedModule.ResolvedFileName,
-					tspath.ComparePathsOptions{
-						UseCaseSensitiveFileNames: c.program.UseCaseSensitiveFileNames(),
-						CurrentDirectory:          c.program.GetCurrentDirectory(),
-					},
-				)
-				c.error(
-					errorNode,
-					diagnostics.This_relative_import_path_is_unsafe_to_rewrite_because_it_looks_like_a_file_name_but_actually_resolves_to_0,
-					relativeToSourceFile,
-				)
-			} else if resolvedModule.ResolvedUsingTsExtension && !shouldRewrite && c.sourceFileMayBeEmitted(sourceFile) {
-				c.error(
-					errorNode,
-					diagnostics.This_import_uses_a_0_extension_to_resolve_to_an_input_TypeScript_file_but_will_not_be_rewritten_during_emit_because_it_is_not_a_relative_path,
-					tspath.GetAnyExtensionFromPath(moduleReference, nil, false),
-				)
-			}
-			// TODO: Add project reference check when GetResolvedProjectReferenceToRedirect is implemented
 		}
 
 		if sourceFile.Symbol != nil {

testdata/baselines/reference/submodule/conformance/cjsErrors(module=node18).errors.txt

@@ -0,0 +1,12 @@
+index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+
+
+==== index.ts (1 errors) ====
+    import foo = require("./foo.ts"); // Error
+                         ~~~~~~~~~~
+!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+    import type _foo = require("./foo.ts"); // Ok
+    
+==== foo.ts/index.ts (0 errors) ====
+    export = {};
+    

testdata/baselines/reference/submodule/conformance/cjsErrors(module=node18).errors.txt.diff

@@ -2,15 +2,14 @@
 +++ new.cjsErrors(module=node18).errors.txt
 @@= skipped -0, +0 lines =@@
 -index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "./foo.ts/index.ts".
--
--
--==== index.ts (1 errors) ====
--    import foo = require("./foo.ts"); // Error
--                         ~~~~~~~~~~
++index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+
+
+ ==== index.ts (1 errors) ====
+     import foo = require("./foo.ts"); // Error
+                          ~~~~~~~~~~
 -!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "./foo.ts/index.ts".
--    import type _foo = require("./foo.ts"); // Ok
--    
--==== foo.ts/index.ts (0 errors) ====
--    export = {};
--    
-+<no content>
++!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+     import type _foo = require("./foo.ts"); // Ok
+     
+ ==== foo.ts/index.ts (0 errors) ====

testdata/baselines/reference/submodule/conformance/cjsErrors(module=nodenext).errors.txt

@@ -0,0 +1,12 @@
+index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+
+
+==== index.ts (1 errors) ====
+    import foo = require("./foo.ts"); // Error
+                         ~~~~~~~~~~
+!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+    import type _foo = require("./foo.ts"); // Ok
+    
+==== foo.ts/index.ts (0 errors) ====
+    export = {};
+    

testdata/baselines/reference/submodule/conformance/cjsErrors(module=nodenext).errors.txt.diff

@@ -2,15 +2,14 @@
 +++ new.cjsErrors(module=nodenext).errors.txt
 @@= skipped -0, +0 lines =@@
 -index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "./foo.ts/index.ts".
--
--
--==== index.ts (1 errors) ====
--    import foo = require("./foo.ts"); // Error
--                         ~~~~~~~~~~
++index.ts(1,22): error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+
+
+ ==== index.ts (1 errors) ====
+     import foo = require("./foo.ts"); // Error
+                          ~~~~~~~~~~
 -!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "./foo.ts/index.ts".
--    import type _foo = require("./foo.ts"); // Ok
--    
--==== foo.ts/index.ts (0 errors) ====
--    export = {};
--    
-+<no content>
++!!! error TS2876: This relative import path is unsafe to rewrite because it looks like a file name, but actually resolves to "foo.ts/index.ts".
+     import type _foo = require("./foo.ts"); // Ok
+     
+ ==== foo.ts/index.ts (0 errors) ====