Terminal: keep the screen in the history when it is cleared

terminal/bundles/org.eclipse.terminal.control/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.terminal.control; singleton:=true
-Bundle-Version: 1.1.200.qualifier
+Bundle-Version: 1.1.300.qualifier
 Bundle-Activator: org.eclipse.terminal.internal.control.impl.TerminalPlugin
 Bundle-Vendor: %providerName
 Bundle-Localization: plugin

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/emulator/VT100EmulatorBackend.java

@@ -196,12 +196,37 @@ public void eraseToCursor() {
 	@Override
 	public void eraseAll() {
 		synchronized (fTerminal) {
+			// What is on the screen goes into the history before it is erased, as in
+			// Windows Terminal and VTE, so that clearing the screen does not destroy
+			// what the user was reading. It matters on Windows, where ConPTY clears
+			// the screen at the start of every connection. Blank lines at the bottom
+			// of the screen are left out. Where the buffer is capped at the screen,
+			// as on an alternate screen, the lines simply go.
+			int used = fLines;
+			while (used > 0 && isBlank(toAbsoluteLine(used - 1))) {
+				used--;
+			}
+			for (int i = 0; i < used; i++) {
+				fTerminal.addLine();
+			}
 			for (int line = toAbsoluteLine(0); line < toAbsoluteLine(fLines); line++) {
 				fTerminal.cleanLine(line);
 			}
 		}
 	}
 
+	private boolean isBlank(int line) {
+		char[] chars = fTerminal.getChars(line);
+		if (chars != null) {
+			for (char c : chars) {
+				if (c != '\000' && c != ' ') {
+					return false;
+				}
+			}
+		}
+		return true;
+	}
+
 	@Override
 	public void eraseLine() {
 		synchronized (fTerminal) {

terminal/tests/org.eclipse.terminal.test/src/org/eclipse/terminal/internal/emulator/VT100EmulatorBackendTest.java

@@ -24,6 +24,7 @@
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import org.eclipse.terminal.internal.model.TerminalTextData;
 import org.eclipse.terminal.internal.model.TerminalTextDataStore;
 import org.eclipse.terminal.internal.model.TerminalTextTestHelper;
 import org.eclipse.terminal.model.ITerminalTextData;
@@ -318,7 +319,30 @@ public void testEraseAll() {
 		vt100.setDimensions(3, 4);
 		fill(term, "0000\n" + "1111\n" + "2222\n" + "3333\n" + "4444\n" + "5555");
 		vt100.eraseAll();
-		assertEqualsTerm("0000\n" + "1111\n" + "2222\n" + "    \n" + "    \n" + "    ", toMultiLineText(term));
+		// the screen goes into the history; with no room to grow, the oldest lines make way
+		assertEqualsTerm("3333\n" + "4444\n" + "5555\n" + "    \n" + "    \n" + "    ", toMultiLineText(term));
+	}
+
+	@Test
+	public void testEraseAllKeepsTheScreenInHistory() {
+		// also on the buffer the terminal actually uses
+		for (ITerminalTextData term : new ITerminalTextData[] { makeITerminalTextData(), new TerminalTextData() }) {
+			IVT100EmulatorBackend vt100 = makeBakend(term);
+			term.setMaxHeight(100);
+			vt100.setDimensions(4, 4);
+			fill(term, "0000\n" + "1111\n" + "2222\n" + "3333\n" + "4444\n" + "    ");
+			vt100.setCursor(2, 1);
+			vt100.eraseAll();
+			// the screen was 2222, 3333, 4444 and a blank line, which is not kept
+			assertEqualsTerm("0000\n" + "1111\n" + "2222\n" + "3333\n" + "4444\n" + "    \n" + "    \n" + "    \n" + "    ",
+					toMultiLineText(term));
+			// erasing does not move the cursor
+			assertEquals(2, vt100.getCursorLine());
+			assertEquals(1, vt100.getCursorColumn());
+			// a blank screen adds nothing
+			vt100.eraseAll();
+			assertEquals(9, term.getHeight());
+		}
 	}
 
 	@Test

terminal/tests/org.eclipse.terminal.test/src/org/eclipse/terminal/internal/emulator/VT100EmulatorTest.java

@@ -274,6 +274,21 @@ public void testClear() {
 		assertAll(() -> assertCursorLocation(0, 0), () -> assertTextEquals(""));
 	}
 
+	@Test
+	public void testClearScreenKeepsItInHistory() {
+		data.setMaxHeight(1000);
+		for (int i = 0; i < 30; i++) {
+			run("Hello " + i + "\r\n");
+		}
+		// what ConPTY sends at the start of every connection on Windows
+		run(CLEAR_ENTIRE_SCREEN + "\u001b[m" + CURSOR_POSITION_TOP_LEFT + "prompt$ ");
+		int top = data.getHeight() - WINDOW_LINES; // first line of the screen
+		assertAll(() -> assertEquals("Hello 29", new String(data.getChars(top - 1)).trim()),
+				() -> assertEquals("Hello 0", new String(data.getChars(0)).trim()),
+				() -> assertEquals("prompt$", new String(data.getChars(top)).replace('\000', ' ').trim()),
+				() -> assertCursorLocation(top, 8)); // the top of the screen, counted in the buffer
+	}
+
 	/**
 	 * Runs what "up arrow" would send back to terminal in less/man/etc.
 	 */