Add --color support to bootstrap

This allows using bootstrap with https://github.com/Canop/bacon.

src/bootstrap/builder.rs

@@ -19,7 +19,7 @@ use crate::compile;
 use crate::config::TargetSelection;
 use crate::dist;
 use crate::doc;
-use crate::flags::Subcommand;
+use crate::flags::{Color, Subcommand};
 use crate::install;
 use crate::native;
 use crate::run;
@@ -811,6 +811,16 @@ impl<'a> Builder<'a> {
             cargo.env("REAL_LIBRARY_PATH", e);
         }
 
+        match self.build.config.color {
+            Color::Always => {
+                cargo.arg("--color=always");
+            }
+            Color::Never => {
+                cargo.arg("--color=never");
+            }
+            Color::Auto => {} // nothing to do
+        }
+
         if cmd != "install" {
             cargo.arg("--target").arg(target.rustc_target_arg());
         } else {

src/bootstrap/config.rs

@@ -13,8 +13,8 @@ use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
 use crate::cache::{Interned, INTERNER};
-use crate::flags::Flags;
 pub use crate::flags::Subcommand;
+use crate::flags::{Color, Flags};
 use crate::util::exe;
 use build_helper::t;
 use merge::Merge;
@@ -67,6 +67,7 @@ pub struct Config {
     pub json_output: bool,
     pub test_compare_mode: bool,
     pub llvm_libunwind: Option<LlvmLibunwind>,
+    pub color: Color,
 
     pub on_fail: Option<String>,
     pub stage: u32,
@@ -577,6 +578,7 @@ impl Config {
         config.keep_stage = flags.keep_stage;
         config.keep_stage_std = flags.keep_stage_std;
         config.bindir = "bin".into(); // default
+        config.color = flags.color;
         if let Some(value) = flags.deny_warnings {
             config.deny_warnings = value;
         }

src/bootstrap/flags.rs

@@ -15,6 +15,31 @@ use crate::config::{Config, TargetSelection};
 use crate::setup::Profile;
 use crate::{Build, DocTests};
 
+pub enum Color {
+    Always,
+    Never,
+    Auto,
+}
+
+impl Default for Color {
+    fn default() -> Self {
+        Self::Auto
+    }
+}
+
+impl std::str::FromStr for Color {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.to_lowercase().as_str() {
+            "always" => Ok(Self::Always),
+            "never" => Ok(Self::Never),
+            "auto" => Ok(Self::Auto),
+            _ => Err(()),
+        }
+    }
+}
+
 /// Deserialized version of all flags for this compile.
 pub struct Flags {
     pub verbose: usize, // number of -v args; each extra -v after the first is passed to Cargo
@@ -34,6 +59,7 @@ pub struct Flags {
     pub rustc_error_format: Option<String>,
     pub json_output: bool,
     pub dry_run: bool,
+    pub color: Color,
 
     // This overrides the deny-warnings configuration option,
     // which passes -Dwarnings to the compiler invocations.
@@ -184,6 +210,7 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`",
         );
         opts.optopt("", "error-format", "rustc error format", "FORMAT");
         opts.optflag("", "json-output", "use message-format=json");
+        opts.optopt("", "color", "whether to use color in cargo and rustc output", "STYLE");
         opts.optopt(
             "",
             "llvm-skip-rebuild",
@@ -644,6 +671,9 @@ Arguments:
             llvm_skip_rebuild: matches.opt_str("llvm-skip-rebuild").map(|s| s.to_lowercase()).map(
                 |s| s.parse::<bool>().expect("`llvm-skip-rebuild` should be either true or false"),
             ),
+            color: matches
+                .opt_get_default("color", Color::Auto)
+                .expect("`color` should be `always`, `never`, or `auto`"),
         }
     }
 }