Auto merge of #12727 - ehuss:buffered-shell, r=epage

Buffer console status messages.

This adds buffering to some of the console output. This can help with interleaved output, particularly with things like the log output interleaving with status messages. This fixes that interleaving by atomically writing the entire status message, which in turn, helps fix some spurious errors such as https://github.com/rust-lang/cargo/issues/12639.

I'm uncertain what the performance impact of this change might have. It might improve performance, since there should be a lot fewer syscalls, and I suspect terminals will be able to handle it more efficiently (and particularly across a network connection). However, I don't know if that will have a noticeable impact.

Only the "status" messages are buffered. Everything else is still unbuffered as before.

src/cargo/core/shell.rs

@@ -4,7 +4,7 @@ use std::io::IsTerminal;
 
 use anstyle::Style;
 use anstyle_termcolor::to_termcolor_spec;
-use termcolor::{self, StandardStream, WriteColor};
+use termcolor::{self, BufferWriter, StandardStream, WriteColor};
 
 use crate::util::errors::CargoResult;
 use crate::util::style::*;
@@ -81,9 +81,15 @@ enum ShellOut {
     /// A plain write object without color support
     Write(Box<dyn Write>),
     /// Color-enabled stdio, with information on whether color should be used
+    ///
+    /// The separate buffered fields are used for buffered writing to the
+    /// corresponding stream. The non-buffered fields should be used when you
+    /// do not want content to be buffered.
     Stream {
         stdout: StandardStream,
+        buffered_stdout: BufferWriter,
         stderr: StandardStream,
+        buffered_stderr: BufferWriter,
         stderr_tty: bool,
         color_choice: ColorChoice,
     },
@@ -105,10 +111,14 @@ impl Shell {
     /// output.
     pub fn new() -> Shell {
         let auto_clr = ColorChoice::CargoAuto;
+        let stdout_choice = auto_clr.to_termcolor_color_choice(Stream::Stdout);
+        let stderr_choice = auto_clr.to_termcolor_color_choice(Stream::Stderr);
         Shell {
             output: ShellOut::Stream {
-                stdout: StandardStream::stdout(auto_clr.to_termcolor_color_choice(Stream::Stdout)),
-                stderr: StandardStream::stderr(auto_clr.to_termcolor_color_choice(Stream::Stderr)),
+                stdout: StandardStream::stdout(stdout_choice),
+                buffered_stdout: BufferWriter::stdout(stdout_choice),
+                stderr: StandardStream::stderr(stderr_choice),
+                buffered_stderr: BufferWriter::stderr(stderr_choice),
                 color_choice: ColorChoice::CargoAuto,
                 stderr_tty: std::io::stderr().is_terminal(),
             },
@@ -287,7 +297,9 @@ impl Shell {
     pub fn set_color_choice(&mut self, color: Option<&str>) -> CargoResult<()> {
         if let ShellOut::Stream {
             ref mut stdout,
+            ref mut buffered_stdout,
             ref mut stderr,
+            ref mut buffered_stderr,
             ref mut color_choice,
             ..
         } = self.output
@@ -305,8 +317,12 @@ impl Shell {
                 ),
             };
             *color_choice = cfg;
-            *stdout = StandardStream::stdout(cfg.to_termcolor_color_choice(Stream::Stdout));
-            *stderr = StandardStream::stderr(cfg.to_termcolor_color_choice(Stream::Stderr));
+            let stdout_choice = cfg.to_termcolor_color_choice(Stream::Stdout);
+            let stderr_choice = cfg.to_termcolor_color_choice(Stream::Stderr);
+            *stdout = StandardStream::stdout(stdout_choice);
+            *buffered_stdout = BufferWriter::stdout(stdout_choice);
+            *stderr = StandardStream::stderr(stderr_choice);
+            *buffered_stderr = BufferWriter::stderr(stderr_choice);
         }
         Ok(())
     }
@@ -410,21 +426,26 @@ impl ShellOut {
         justified: bool,
     ) -> CargoResult<()> {
         match *self {
-            ShellOut::Stream { ref mut stderr, .. } => {
-                stderr.reset()?;
-                stderr.set_color(&to_termcolor_spec(*style))?;
+            ShellOut::Stream {
+                ref mut buffered_stderr,
+                ..
+            } => {
+                let mut buffer = buffered_stderr.buffer();
+                buffer.reset()?;
+                buffer.set_color(&to_termcolor_spec(*style))?;
                 if justified {
-                    write!(stderr, "{:>12}", status)?;
+                    write!(buffer, "{:>12}", status)?;
                 } else {
-                    write!(stderr, "{}", status)?;
-                    stderr.set_color(termcolor::ColorSpec::new().set_bold(true))?;
-                    write!(stderr, ":")?;
+                    write!(buffer, "{}", status)?;
+                    buffer.set_color(termcolor::ColorSpec::new().set_bold(true))?;
+                    write!(buffer, ":")?;
                 }
-                stderr.reset()?;
+                buffer.reset()?;
                 match message {
-                    Some(message) => writeln!(stderr, " {}", message)?,
-                    None => write!(stderr, " ")?,
+                    Some(message) => writeln!(buffer, " {}", message)?,
+                    None => write!(buffer, " ")?,
                 }
+                buffered_stderr.print(&buffer)?;
             }
             ShellOut::Write(ref mut w) => {
                 if justified {
@@ -444,11 +465,16 @@ impl ShellOut {
     /// Write a styled fragment
     fn write_stdout(&mut self, fragment: impl fmt::Display, color: &Style) -> CargoResult<()> {
         match *self {
-            ShellOut::Stream { ref mut stdout, .. } => {
-                stdout.reset()?;
-                stdout.set_color(&to_termcolor_spec(*color))?;
-                write!(stdout, "{}", fragment)?;
-                stdout.reset()?;
+            ShellOut::Stream {
+                ref mut buffered_stdout,
+                ..
+            } => {
+                let mut buffer = buffered_stdout.buffer();
+                buffer.reset()?;
+                buffer.set_color(&to_termcolor_spec(*color))?;
+                write!(buffer, "{}", fragment)?;
+                buffer.reset()?;
+                buffered_stdout.print(&buffer)?;
             }
             ShellOut::Write(ref mut w) => {
                 write!(w, "{}", fragment)?;
@@ -460,11 +486,16 @@ impl ShellOut {
     /// Write a styled fragment
     fn write_stderr(&mut self, fragment: impl fmt::Display, color: &Style) -> CargoResult<()> {
         match *self {
-            ShellOut::Stream { ref mut stderr, .. } => {
-                stderr.reset()?;
-                stderr.set_color(&to_termcolor_spec(*color))?;
-                write!(stderr, "{}", fragment)?;
-                stderr.reset()?;
+            ShellOut::Stream {
+                ref mut buffered_stderr,
+                ..
+            } => {
+                let mut buffer = buffered_stderr.buffer();
+                buffer.reset()?;
+                buffer.set_color(&to_termcolor_spec(*color))?;
+                write!(buffer, "{}", fragment)?;
+                buffer.reset()?;
+                buffered_stderr.print(&buffer)?;
             }
             ShellOut::Write(ref mut w) => {
                 write!(w, "{}", fragment)?;