LS completions relevance in Java editor (#1223)

Rather than just push LS proposals at the top of the proposals list
attempt to compute relevance in java editor completion terms. Compute
base relevance based on LSP4E proposal category and rank.

Author: BoykoAlex

org.eclipse.lsp4e.jdt/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: JDT Integration for LSP4E
 Bundle-SymbolicName: org.eclipse.lsp4e.jdt;singleton:=true
-Bundle-Version: 0.13.4.qualifier
+Bundle-Version: 0.13.5.qualifier
 Automatic-Module-Name: org.eclipse.lsp4e.jdt
 Bundle-RequiredExecutionEnvironment: JavaSE-17
 Bundle-ClassPath: .
@@ -14,4 +14,5 @@ Require-Bundle: org.eclipse.core.runtime;bundle-version="3.12.0",
  org.eclipse.lsp4e;bundle-version="0.18.13",
  org.eclipse.jdt.core;bundle-version="3.20.0",
  org.eclipse.jdt.ui;bundle-version="3.20.0",
- org.eclipse.swt
+ org.eclipse.swt,
+ org.eclipse.lsp4j

org.eclipse.lsp4e.jdt/src/org/eclipse/lsp4e/jdt/LSJavaProposal.java

@@ -12,6 +12,7 @@
 package org.eclipse.lsp4e.jdt;
 
 import org.eclipse.jdt.annotation.Nullable;
+import org.eclipse.jdt.internal.codeassist.RelevanceConstants;
 import org.eclipse.jdt.ui.text.java.IJavaCompletionProposal;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.contentassist.ICompletionProposal;
@@ -20,10 +21,22 @@
 import org.eclipse.swt.graphics.Image;
 import org.eclipse.swt.graphics.Point;
 
+@SuppressWarnings("restriction")
 class LSJavaProposal implements IJavaCompletionProposal {
+	
+	private static final int LS_DEFAULT_RELEVANCE = 18;
+	
+	private static final int MAX_BASE_RELEVANCE = 51 * 16; // Looks like JDT's max for exact match is 52
+	
+	 // Based on org.eclipse.jdt.internal.ui.text.java.RelevanceComputer
+	private static final int DEFAULT_RELEVANCE = (RelevanceConstants.R_DEFAULT + LS_DEFAULT_RELEVANCE) * 16;
 
-	protected ICompletionProposal delegate;
+	private static final int RANGE_WITHIN_CATEGORY = Math.round((MAX_BASE_RELEVANCE - DEFAULT_RELEVANCE) / 4);
 
+	protected ICompletionProposal delegate;
+	private boolean relevanceComputed = false;
+	private int relevance = -1;
+	
 	public LSJavaProposal(ICompletionProposal delegate) {
 		this.delegate = delegate;
 	}
@@ -60,11 +73,39 @@ public String getDisplayString() {
 
 	@Override
 	public int getRelevance() {
-		if (delegate instanceof LSCompletionProposal) {
-			int rankScore = ((LSCompletionProposal) delegate).getRankScore();
-			return 1000 - rankScore;
+		if (!relevanceComputed) {
+			if (delegate instanceof LSCompletionProposal c) {
+				// Based on org.eclipse.jdt.internal.ui.text.java.RelevanceComputer
+				relevance = computeBaseRelevance(c);
+				switch (c.getItem().getKind()) {
+				case Class:
+					relevance += 3;
+					break;
+				case Field:
+				case Property:	
+					relevance += 5;
+					break;
+				case Method:
+					relevance += 4;
+					break;
+				case Variable:
+				case Value:
+					relevance += 6;
+					break;
+				default:
+				}
+			}
+			relevanceComputed = true;
 		}
-		return -1;
+		return relevance;
+	}
+	
+	private int computeBaseRelevance(LSCompletionProposal c) {
+		// Incorporate LSP4E category and rank into base relevance.
+		int base = MAX_BASE_RELEVANCE - (c.getRankCategory() - 1) * RANGE_WITHIN_CATEGORY;
+		int rank = c.getRankScore();
+		base -= (rank >= 0 && rank < RANGE_WITHIN_CATEGORY ? rank : RANGE_WITHIN_CATEGORY);
+		return base;
 	}
 
 }