Avoid compile on save for declaration files

Author: Ben Lichtman

src/server/session.ts

@@ -1604,15 +1604,22 @@ namespace ts.server {
                 path => this.projectService.getScriptInfoForPath(path)!,
                 projects,
                 (project, info) => {
-                    let result: protocol.CompileOnSaveAffectedFileListSingleProject | undefined;
-                    if (project.compileOnSaveEnabled && project.languageServiceEnabled && !project.isOrphan() && !project.getCompilationSettings().noEmit) {
-                        result = {
-                            projectFileName: project.getProjectName(),
-                            fileNames: project.getCompileOnSaveAffectedFileList(info),
-                            projectUsesOutFile: !!project.getCompilationSettings().outFile || !!project.getCompilationSettings().out
-                        };
+                    if (!project.compileOnSaveEnabled || !project.languageServiceEnabled || project.isOrphan()) {
+                        return undefined;
+                    }
+
+                    const compilationSettings = project.getCompilationSettings();
+
+                    if (!!compilationSettings.noEmit || fileExtensionIs(info.fileName, Extension.Dts) && !getEmitDeclarations(compilationSettings)) {
+                        // avoid triggering emit when a change is made in a .d.ts when declaration emit is disabled
+                        return undefined;
                     }
-                    return result;
+
+                    return {
+                        projectFileName: project.getProjectName(),
+                        fileNames: project.getCompileOnSaveAffectedFileList(info),
+                        projectUsesOutFile: !!compilationSettings.outFile || !!compilationSettings.out
+                    };
                 }
             );
         }