Address PR feedback: expand ternary return into if block, add check to ensure proper options usage

Author: masaeedu

src/compiler/program.ts

@@ -1669,6 +1669,10 @@ namespace ts {
                     programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "sourceRoot", "sourceMap"));
                 }
             }
+            
+            if(!options.declaration && options.declarationDir) {
+                programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_0_cannot_be_specified_without_specifying_option_1, "declarationDir", "declaration"));
+            }
 
             const languageVersion = options.target || ScriptTarget.ES3;
             const outFile = options.outFile || options.out;

src/compiler/utilities.ts

@@ -2015,11 +2015,13 @@ namespace ts {
     export function getDeclarationEmitOutputFilePath(sourceFile: SourceFile, host: EmitHost) {
         const options = host.getCompilerOptions();
         const outputDir = options.declarationDir || options.outDir; // Prefer declaration folder if specified
-        return options.declaration ? removeFileExtension(
-            outputDir
+        
+        if (options.declaration) {
+            const path = outputDir
                 ? getSourceFilePathInNewDir(sourceFile, host, outputDir)
-                : sourceFile.fileName
-        ) + ".d.ts" : undefined;
+                : sourceFile.fileName;
+            return removeFileExtension(path) + ".d.ts";
+        }
     }
 
     export function getEmitScriptTarget(compilerOptions: CompilerOptions) {