fix: LSCompletionProposal#getContextInformationPosition (#1345)

For some odd reason `LSCompletionProposal.getContextInformationPosition`
currently returns `SWT.RIGHT` hardcoded which translates to int value
`131072`. I changed the information to return the beginning of the text
edit range.

Author: sebthom

org.eclipse.lsp4e.test/src/org/eclipse/lsp4e/test/completion/CompleteCompletionTest.java

@@ -576,4 +576,28 @@ public void testCancellation() throws Exception {
 		CompletableFuture.runAsync(() -> contentAssistProcessor.computeCompletionProposals(viewer, 1));
 		DisplayHelper.waitAndAssertCondition(viewer.getTextWidget().getDisplay(), () -> assertEquals(1, MockConnectionProvider.cancellations.size()));
 	}
+
+	/**
+	 * Verifies context information position returned by LSCompletionProposal uses
+	 * the start of the edit range when available.
+	 */
+	@Test
+	public void testContextInformationPositionUsesEditRangeStart() throws CoreException {
+		final int editOffset = 2;
+		CompletionItem completionItem = createCompletionItem( //
+				"hello", //
+				CompletionItemKind.Text, //
+				new Range(new Position(0, editOffset), new Position(0, editOffset + 1)));
+		MockLanguageServer.INSTANCE.setCompletionList(new CompletionList(true, List.of(completionItem)));
+
+		ITextViewer viewer = TestUtils.openTextViewer(TestUtils.createUniqueTestFile(project, "ABCDE"));
+
+		// Invoke completion at the start of the TextEdit range (offset 2)
+		ICompletionProposal[] proposals = contentAssistProcessor.computeCompletionProposals(viewer, editOffset);
+		assertEquals(1, proposals.length);
+
+		int pos = ((LSCompletionProposal) proposals[0]).getContextInformationPosition();
+		// TextEdit starts at (0,2) so offset should be 0
+		assertEquals(editOffset, pos);
+	}
 }

org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/completion/LSCompletionProposal.java

@@ -83,7 +83,6 @@
 import org.eclipse.lsp4j.ServerCapabilities;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.jsonrpc.messages.Either;
-import org.eclipse.swt.SWT;
 import org.eclipse.swt.graphics.Image;
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.graphics.TextStyle;
@@ -875,6 +874,11 @@ public void apply(IDocument document) {
 
 	@Override
 	public int getContextInformationPosition() {
-		return SWT.RIGHT;
+		try {
+			return LSPEclipseUtils.toOffset(getTextEditRange().getStart(), document);
+		} catch (BadLocationException e) {
+			LanguageServerPlugin.logWarning(e.getMessage(), e);
+		}
+		return bestOffset;
 	}
 }