fix: Formatting fails when position end is out of range of the document

Fixes redhat-developer#183

Signed-off-by: azerr <[email protected]>

src/main/java/com/redhat/devtools/lsp4ij/LSPIJUtils.java

@@ -262,9 +262,18 @@ public static Module getModule(@Nullable VirtualFile file, @NotNull Project proj
         return ReadAction.compute(() -> ProjectFileIndex.getInstance(project).getModuleForFile(file, false));
     }
 
-    public static int toOffset(Position start, Document document) throws IndexOutOfBoundsException {
-        int lineStartOffset = document.getLineStartOffset(start.getLine());
-        return lineStartOffset + start.getCharacter();
+    public static int toOffset(Position position, Document document) throws IndexOutOfBoundsException {
+        // Adjust position line/character according to this comment https://github.com/microsoft/vscode-languageserver-node/blob/ed3cd0f78c1495913bda7318ace2be7f968008af/textDocument/src/main.ts#L26
+        int line = position.getLine();
+        if (line < 0) {
+            // If a line number is negative, it defaults to 0.
+            line = 0;
+        } else {
+            // If a line number is greater than the number of lines in a document, it defaults back to the number of lines in the document.
+            line = Math.min(line, document.getLineCount() - 1);
+        }
+        int lineStartOffset = document.getLineStartOffset(line);
+        return lineStartOffset + position.getCharacter();
     }
 
     public static Position toPosition(int offset, Document document) {

src/test/java/com/redhat/devtools/lsp4ij/LSPIJUtils_toOffsetTest.java

@@ -0,0 +1,61 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Red Hat, Inc.
+ * Distributed under license by Red Hat, Inc. All rights reserved.
+ * This program is made available under the terms of the
+ * Eclipse Public License v2.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v20.html
+ *
+ * Contributors:
+ * Red Hat, Inc. - initial API and implementation
+ ******************************************************************************/
+package com.redhat.devtools.lsp4ij;
+
+import com.intellij.openapi.editor.Document;
+import com.intellij.openapi.editor.impl.DocumentImpl;
+import com.intellij.testFramework.fixtures.BasePlatformTestCase;
+import org.eclipse.lsp4j.Position;
+
+/**
+ * Tests for {@link LSPIJUtils#toOffset(Position, Document)}.
+ */
+public class LSPIJUtils_toOffsetTest extends BasePlatformTestCase {
+
+    public void testValidPositionAtFirstLine() {
+        assertOffset("foo", 0, 0, 0, 'f');
+        assertOffset("foo", 0, 1, 1, 'o');
+        assertOffset("foo", 0, 2, 2, 'o');
+    }
+
+    public void testValidPositionAtSecondLine() {
+        assertOffset("foo\nbar", 1, 0, 4, 'b');
+        assertOffset("foo\nbar", 1, 1, 5, 'a');
+        assertOffset("foo\nbar", 1, 2, 6, 'r');
+    }
+
+    public void testInvalidLineWithOneLine() {
+        assertOffset("foo", 999999, 0, 0, 'f');
+        assertOffset("foo", 999999, 1, 1, 'o');
+        assertOffset("foo", 999999, 2, 2, 'o');
+    }
+
+    public void testInvalidLineWithTwoLines() {
+        assertOffset("foo\nbar", 999999, 0, 4, 'b');
+        assertOffset("foo\nbar", 999999, 1, 5, 'a');
+        assertOffset("foo\nbar", 999999, 2, 6, 'r');
+    }
+
+    public void assertOffset(String content, int line, int character, int expectedOffset, char expectedChar) {
+        assertOffset(content, new Position(line, character),expectedOffset, expectedChar);
+    }
+
+    public void assertOffset(String content, Position position, int expectedOffset, char expectedChar) {
+        Document document = new DocumentImpl(content);
+        int actualOffset = LSPIJUtils.toOffset(position, document);
+        assertEquals(expectedOffset, actualOffset);
+        // get the character from the given offset
+        char actualChar = document.getCharsSequence().charAt(expectedOffset);
+        assertEquals(expectedChar, actualChar);
+    }
+
+
+}