Fix offset&length computation.

Author: toinehartman

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/util/locations/impl/ArrayLineOffsetMap.java

@@ -78,8 +78,9 @@ public int translateInverseColumn(int line, int column, boolean isEnd) {
 
     @Override
     public Pair<Integer, Integer> translateInverseOffsetLength(int beginLine, int beginColumn, int endLine, int endColumn, int offset, int length) {
-        int offsetOffset = 0;
-        int lengthOffset = 0;
+        assert beginLine <= endLine : "beginLine cannot be larger than endLine";
+        int startOffset = 0;
+        int endOffset = 0;
 
         for (int line = 0; line <= endLine; line++) {
             int lineIndex = lines.search(line);
@@ -88,13 +89,23 @@ public Pair<Integer, Integer> translateInverseOffsetLength(int beginLine, int be
                 continue;
             }
             var lineOffsets = wideColumnOffsetsInverse.get(lineIndex);
-            if (line < beginLine) {
-                offsetOffset += (translateColumnForLine(lineOffsets, beginColumn, false) - beginColumn);
+            if (line <= beginLine) {
+                // offset counts characters up until the beginning of the range
+                startOffset += translateColumnForLine(lineOffsets, beginColumn, false);
+            }
+
+            if (line >= beginLine) {
+                if (line < endLine) {
+                    // offset of full line
+                    endOffset += translateColumnForLine(lineOffsets, Integer.MAX_VALUE, true);
+                } else {
+                    // offset until end column
+                    endOffset += translateColumnForLine(lineOffsets, endColumn, true);
+                }
             }
-            lengthOffset += (translateColumnForLine(lineOffsets, endColumn, true) - endColumn);
         }
 
-        return Pair.of(offset - offsetOffset, length - lengthOffset);
+        return Pair.of(offset - startOffset, length + startOffset - endOffset);
     }
 
     @SuppressWarnings("java:S3776") // parsing tends to be complex

rascal-lsp/src/test/java/engineering/swat/rascal/lsp/util/LineColumnOffsetMapTests.java

@@ -28,6 +28,7 @@
 
 import static org.junit.Assert.assertEquals;
 
+import org.apache.commons.lang3.tuple.Pair;
 import org.junit.Test;
 import org.rascalmpl.vscode.lsp.util.locations.LineColumnOffsetMap;
 import org.rascalmpl.vscode.lsp.util.locations.impl.ArrayLineOffsetMap;
@@ -60,6 +61,8 @@ public void doubleChars() {
     public void noUnicodeCharsInverse() {
         LineColumnOffsetMap map = ArrayLineOffsetMap.build("1234\n1234");
         assertEquals(2, map.translateInverseColumn(0, 2, false));
+        assertEquals(Pair.of(0, 2), map.translateInverseOffsetLength(0, 0, 0, 2, 0, 2));
+        assertEquals(Pair.of(0, 8), map.translateInverseOffsetLength(0, 0, 1, 4, 0, 8));
     }
 
     @Test
@@ -68,6 +71,9 @@ public void singleWideCharInverse() {
         assertEquals(3, map.translateInverseColumn(0, 3, false));
         assertEquals(3, map.translateInverseColumn(0, 4, false));
         assertEquals(4, map.translateInverseColumn(0, 5, false));
+        assertEquals(Pair.of(3, 1), map.translateInverseOffsetLength(0, 2, 0, 4, 3, 2));
+        assertEquals(Pair.of(3, 1), map.translateInverseOffsetLength(0, 4, 0, 5, 4, 1));
+        assertEquals(Pair.of(0, 10), map.translateInverseOffsetLength(0, 0, 1, 6, 0, 12));
     }
 
 
@@ -77,6 +83,8 @@ public void doubleCharsInverse() {
         assertEquals(5, map.translateInverseColumn(0, 6, false));
         assertEquals(5, map.translateInverseColumn(0, 7, true));
         assertEquals(6, map.translateInverseColumn(0, 8, false));
+        assertEquals(Pair.of(2, 1), map.translateInverseOffsetLength(0, 2, 0, 4, 2, 2));
+        assertEquals(Pair.of(2, 3), map.translateInverseOffsetLength(0, 2, 0, 7, 2, 5));
     }
 
 }