experimental UI: honor --curses

Bazel can be asked to uses colors, but not to use other curses options.
In this case, the ExperimentalEventHandler cannot rely on the terminal
to ignore all curses output; hence it has to actively refrain from using
curses that move the cursor.

--
Change-Id: I026edade4366a8c5a8e56d376e8a4603f5c73b92
Reviewed-on: https://bazel-review.googlesource.com/#/c/3291
MOS_MIGRATED_REVID=119439855

src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java

@@ -42,6 +42,7 @@
 public class ExperimentalEventHandler extends BlazeCommandEventHandler {
   private static Logger LOG = Logger.getLogger(ExperimentalEventHandler.class.getName());
 
+  private final boolean cursorControl;
   private final AnsiTerminal terminal;
   private final boolean debugAllEvents;
   private final ExperimentalStateTracker stateTracker;
@@ -54,6 +55,7 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
   public ExperimentalEventHandler(
       OutErr outErr, BlazeCommandEventHandler.Options options, Clock clock) {
     super(outErr, options);
+    this.cursorControl = options.useCursorControl();
     this.terminal = new AnsiTerminal(outErr.getErrorStream());
     this.terminalWidth = (options.terminalColumns > 0 ? options.terminalColumns : 80);
     this.debugAllEvents = options.experimentalUiDebugAllEvents;
@@ -224,6 +226,9 @@ public void resetTerminal() {
   }
 
   private void clearProgressBar() throws IOException {
+    if (!cursorControl) {
+      return;
+    }
     for (int i = 0; i < numLinesProgressBar; i++) {
       terminal.cr();
       terminal.cursorUp(1);

src/test/shell/integration/experimental_ui_test.sh

@@ -67,6 +67,19 @@ function test_basic_progress() {
   expect_log $'\x1b\[1A\x1b\[K'
 }
 
+function test_basic_progress_no_curses() {
+  bazel test --experimental_ui --curses=no --color=yes pkg:true 2>$TEST_log \
+    || fail "bazel test failed"
+  # some progress indicator is shown
+  expect_log '\[[0-9,]* / [0-9,]*\]'
+  # cursor is not moved up
+  expect_not_log $'\x1b\[1A'
+  # no line is deleted
+  expect_not_log $'\x1b\[K'
+  # but some green color is used
+  expect_log $'\x1b\[32m'
+}
+
 function test_pass() {
   bazel test --experimental_ui --curses=yes --color=yes pkg:true >$TEST_log || fail "bazel test failed"
   # PASS is written in green on the same line as the test target