feat: Add new lint rule for the directive KillMode

src/diagnostics.ts

@@ -12,6 +12,7 @@ import {
 export const enum SystemdDiagnosticType {
     unknownDirective = 1,
     deprecatedDirective = 2,
+    deprecatedValue = 3,
 }
 export type SystemdDiagnostic = Diagnostic & {
     type?: SystemdDiagnosticType;
@@ -35,6 +36,14 @@ export function getDiagnosticForUnknown(range: Range, directiveName: string): Sy
     return d;
 }
 
+export function getDiagnosticForValue(range: Range, directiveName: string, help: string): SystemdDiagnostic {
+    const d: SystemdDiagnostic = new Diagnostic(range, help);
+    d.severity = DiagnosticSeverity.Warning;
+    d.type = SystemdDiagnosticType.deprecatedValue;
+    d.directive = directiveName;
+    return d;
+}
+
 export class SystemdDiagnosticManager {
     private _collection: DiagnosticCollection;
     private static readonly collectionName = "Systemd";

src/vscode-lint.ts

@@ -16,6 +16,7 @@ import {
     SystemdDiagnosticManager,
     SystemdDiagnosticType,
     getDiagnosticForDeprecated,
+    getDiagnosticForValue,
     getDiagnosticForUnknown,
 } from "./diagnostics";
 import { getDirectiveKeys } from "./parser/get-directive-keys";
@@ -82,6 +83,20 @@ export class SystemdLint implements CodeActionProvider {
                 items.push(getDiagnosticForDeprecated(getRange(), directiveName));
                 return;
             }
+            // example lint:
+            // https://github.com/systemd/systemd/blob/effefa30de46f25d0f50a36210a9835097381c2b/src/core/load-fragment.c#L665
+            if (directiveName === "KillMode") {
+                if (it.value.toLowerCase() === "none") {
+                    const msg =
+                        "Unit uses KillMode=none. " +
+                        "This is unsafe, as it disables systemd's process lifecycle management for the service. " +
+                        "Please update the service to use a safer KillMode=, such as 'mixed' or 'control-group'. " +
+                        "Support for KillMode=none is deprecated and will eventually be removed.";
+                    const d = getDiagnosticForValue(getRange(it.value.length + 1), directiveName, msg);
+                    items.push(d);
+                    return;
+                }
+            }
 
             if (directivePrefixes.find((p) => directiveName.startsWith(p))) return;
             if (managers.hasDirective(directiveNameLC)) return;