Trim console lines that are longer than limit

Fixes: #2465

Author: trancexpress

debug/org.eclipse.debug.tests/src/org/eclipse/debug/tests/console/IOConsoleTests.java

@@ -715,13 +715,52 @@ public void testTrim() throws Exception {
 
 				c.getConsole().setWaterMarks(50, 100);
 				c.waitForScheduledJobs();
-				c.verifyContentByOffset("0123456789", 0);
+				c.verifyContentByOffset("0123456789", 1);
 				assertTrue(c.getDocument().getNumberOfLines() < 15, "Document not trimmed.");
 			}
 			closeConsole(c);
 		}
 	}
 
+	/**
+	 * Check that trimming within a line doesn't split '\r\n'.
+	 */
+	@Test
+	public void testTrimNewline() throws Exception {
+		final IOConsoleTestUtil c = getTestUtil("Test trim newline");
+		try (IOConsoleOutputStream out = c.getDefaultOutputStream()) {
+			c.writeFast("first\n");
+			c.writeFast("0123456789\r\n", out);
+			c.write("last\n");
+			c.verifyContentByLine("first", 0).verifyContentByLine("last", -2);
+			assertTrue(c.getDocument().getNumberOfLines() > 2, "Document not filled.");
+			c.getConsole().setWaterMarks(6, 16);
+			c.waitForScheduledJobs();
+			c.verifyContent("\r\nlast\n");
+			closeConsole(c);
+		}
+	}
+
+	/**
+	 * Check that trimming within a line doesn't split surrogate pairs, e.g.
+	 * emoji symbols.
+	 */
+	@Test
+	public void testTrimSurrogateCharacters() throws Exception {
+		final IOConsoleTestUtil c = getTestUtil("Test trim newline");
+		try (IOConsoleOutputStream out = c.getDefaultOutputStream()) {
+			c.writeFast("first\n");
+			c.writeFast("1😀2😀3\n", out);
+			c.write("last\n");
+			c.verifyContentByLine("first", 0).verifyContentByLine("last", -2);
+			assertTrue(c.getDocument().getNumberOfLines() > 2, "Document not filled.");
+			c.getConsole().setWaterMarks(8, 16);
+			c.waitForScheduledJobs();
+			c.verifyContentByOffset("😀3\nlas", 0);
+			closeConsole(c);
+		}
+	}
+
 	/**
 	 * Some extra tests for IOConsolePartitioner.
 	 */

debug/org.eclipse.ui.console/src/org/eclipse/ui/internal/console/IOConsolePartitioner.java

@@ -1203,6 +1203,16 @@ private void trim(int truncateOffset, boolean truncateToOffsetLineStart) {
 					if (truncateToOffsetLineStart) {
 						int cutoffLine = document.getLineOfOffset(truncateOffset);
 						cutOffset = document.getLineOffset(cutoffLine);
+						// deal with case of one long line
+						int offset = Math.max(cutOffset, truncateOffset);
+						char c = document.getChar(offset);
+						if (c == '\n' && offset > 0 && document.getChar(offset - 1) == '\r') {
+							cutOffset = offset - 1;
+						} else if (!Character.isLowSurrogate(c)) {
+							cutOffset = offset;
+						} else if (offset > 1) {
+							cutOffset = offset - 1;
+						}
 					}
 					if (cutOffset >= length) {
 						updateType = DocUpdateType.TRIM;