Replace common get-or-initialize pattern with utility function (#1004)

* Replace common get-or-initialize pattern with utility function.

* Clarify semantics with better name and documentation.

Author: toinehartman

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/BaseWorkspaceService.java

@@ -84,11 +84,7 @@ public void initialize(ClientCapabilities clientCap, @Nullable List<WorkspaceFol
             this.workspaceFolders.addAll(currentWorkspaceFolders);
         }
 
-        if (capabilities.getWorkspace() == null) {
-            capabilities.setWorkspace(new WorkspaceServerCapabilities());
-        }
-
-        var workspaceCapabilities = capabilities.getWorkspace();
+        var workspaceCapabilities = Nullables.ensureNonNullAndGet(capabilities, ServerCapabilities::getWorkspace, ServerCapabilities::setWorkspace, WorkspaceServerCapabilities::new);
         if (Nullables.has(clientCap.getWorkspace(), WorkspaceClientCapabilities::getWorkspaceFolders)) {
             var folderOptions = new WorkspaceFoldersOptions();
             folderOptions.setSupported(true);

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/parametric/capabilities/FileOperationCapability.java

@@ -103,17 +103,8 @@ private static FileOperationFilter extensionFilter(String ext) {
     }
 
     private static FileOperationsServerCapabilities fileOperationCapabilities(ServerCapabilities caps) {
-        var workspace = caps.getWorkspace();
-        if (workspace == null) {
-            workspace = new WorkspaceServerCapabilities();
-            caps.setWorkspace(workspace);
-        }
-        var fileOps = workspace.getFileOperations();
-        if (fileOps == null) {
-            fileOps = new FileOperationsServerCapabilities();
-            workspace.setFileOperations(fileOps);
-        }
-        return fileOps;
+        var workspace = Nullables.ensureNonNullAndGet(caps, ServerCapabilities::getWorkspace, ServerCapabilities::setWorkspace, WorkspaceServerCapabilities::new);
+        return Nullables.ensureNonNullAndGet(workspace, WorkspaceServerCapabilities::getFileOperations, WorkspaceServerCapabilities::setFileOperations, FileOperationsServerCapabilities::new);
     }
 
     /**

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/rascal/RascalWorkspaceService.java

@@ -41,6 +41,7 @@
 import org.eclipse.lsp4j.ServerCapabilities;
 import org.eclipse.lsp4j.WorkspaceClientCapabilities;
 import org.eclipse.lsp4j.WorkspaceFolder;
+import org.eclipse.lsp4j.WorkspaceServerCapabilities;
 import org.rascalmpl.vscode.lsp.BaseWorkspaceService;
 import org.rascalmpl.vscode.lsp.IBaseTextDocumentService;
 import org.rascalmpl.vscode.lsp.util.Nullables;
@@ -56,10 +57,8 @@ public void initialize(ClientCapabilities clientCap, @Nullable List<WorkspaceFol
             ServerCapabilities capabilities) {
         super.initialize(clientCap, currentWorkspaceFolders, capabilities);
 
-        if (capabilities.getWorkspace().getFileOperations() == null) {
-            capabilities.getWorkspace().setFileOperations(new FileOperationsServerCapabilities());
-        }
-        var fileOperationCapabilities = capabilities.getWorkspace().getFileOperations();
+        var workspaceCap = Nullables.ensureNonNullAndGet(capabilities, ServerCapabilities::getWorkspace, ServerCapabilities::setWorkspace, WorkspaceServerCapabilities::new);
+        var fileOperationCapabilities = Nullables.ensureNonNullAndGet(workspaceCap, WorkspaceServerCapabilities::getFileOperations, WorkspaceServerCapabilities::setFileOperations, FileOperationsServerCapabilities::new);
 
         var rascalFile = new FileOperationPattern("**/*.rsc");
         rascalFile.setMatches(FileOperationPatternKind.File);

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/util/Nullables.java

@@ -26,7 +26,9 @@
  */
 package org.rascalmpl.vscode.lsp.util;
 
+import java.util.function.BiConsumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.checkerframework.checker.nullness.qual.PolyNull;
 
@@ -99,4 +101,24 @@ public static <A, B> boolean has(@Nullable A a, Function<A, @Nullable B> getFunc
         return get(get(a, getFunc1, null), getFunc2, defaultVal);
     }
 
+    /**
+     * Get a value from an object. If it was not set yet (i.e. `null`), initialize and set it before returning.
+     * @param <C> The type of the containing object.
+     * @param <T> The type of the value to get.
+     * @param container The containing object.
+     * @param getter The value getter.
+     * @param setter The value setter. Only called if the value is not initialized yet.
+     * @param initializer The value initializer (e.g. a constructor). Only called if the value is not initialized yet.
+     * @return The gotten value, or the initialized value if was not initialized yet.
+     */
+    public static <C, T> T ensureNonNullAndGet(C container, Function<C, @Nullable T> getter, BiConsumer<C, T> setter, Supplier<T> initializer) {
+        var t = getter.apply(container);
+        if (t == null) {
+            t = initializer.get();
+            setter.accept(container, t);
+            assert getter.apply(container) != null : "Setter should set same value as getter gets";
+        }
+        return t;
+    }
+
 }