[et] Allow disabling the "cute" output mode, so folks can `grep` the logs

[matanlurey]

Forked from #145711 (comment).

It should be reasonable to do something like:

et build --verbose | grep <something>

We could make this yet-another flag, i.e. --no-animations, but I think verbose implying it is also fine?

Wdut?

/cc @gaaclarke

[gaaclarke]

Oh man, well tools like ag will change their output format when they detect they are being piped to another process. git uses the flag --porcelain to indicate output that is verbose and meant to be parsed by another tool.

I think making --verbose imply that is fine and I don't recommend those other approaches.

[chinmaygarde]

Ah, I just filed #147936 which is a duplicate. We need to check that stdout is a terminal type and disable the pretty printing if its not. It is also ok to allow manually disabling pretty printing to terminal types too.

[chinmaygarde]

As an aside, we need to go a bit out our way to fool Xcode since it pretends to be a terminal but can't handle being a terminal quite right. GN does this detection.

[chinmaygarde]

https://api.dart.dev/stable/3.3.4/dart-io/Stdout/hasTerminal.html may be what we need (and the one for stderr).

[matanlurey]

Update: We do some checks for hasTerminal and supportsAnsiEscapes, but it sounds like those are either insufficient, or give false-positives.

[matanlurey]

When I do:

flutter % et build -v | grep supportsAnsiEscapes
supportsAnsiEscapes: false | hasTerminal: false

... it appears detection does work, so I'm assuming we're not guarding something we should be.

[matanlurey]

The fix is as simple as:

diff --git a/tools/engine_tool/lib/src/logger.dart b/tools/engine_tool/lib/src/logger.dart
index 28bd847885..8b4565d94b 100644
--- a/tools/engine_tool/lib/src/logger.dart
+++ b/tools/engine_tool/lib/src/logger.dart
@@ -169,6 +169,8 @@ class Logger {
   /// and emits a carriage return.
   void clearLine() {
     if (!io.stdout.hasTerminal || _test) {
+      // Just emit a newline in tests or when not connected to a terminal.
+      _ioSinkWrite(io.stdout, '\n');
       return;
     }

However, it is next to impossible to test because the Logger does a bunch of things with global state.

I'm going to provide a bit more TLC to logger.dart and then land the fix.