Auto merge of #38072 - nikomatsakis:bootstrap-incremental, r=acrichto

add preliminary support for incremental compilation to rustbuild.py

This implements the integration described in #37929. It requires the use of a local nightly as your bootstrap compiler. The setup is described in `src/bootstrap/README.md`.

This does NOT implement the "copy stage0 libs to stage1" optimization described in #37929, just because that seems orthogonal to me.

In local testing, I do not yet see any incremental re-use when building rustc. I'm not sure why that is, more investigation needed.

(For these reasons, this is not marked as fixing the relevant issue.)

r? @alexcrichton -- I included one random cleanup (`Step::noop()`) that turned out to not be especially relevant. Feel free to tell me you liked it better the old way.

1 files changed, 26 insertions, 3 deletions

diff --git a/src/bootstrap/flags.rs b/src/bootstrap/flags.rs
index 5c8d7cab966..e5ace62406a 100644
--- a/src/bootstrap/flags.rs
+++ b/src/bootstrap/flags.rs
@@ -27,7 +27,7 @@ use step;
 
 /// Deserialized version of all flags for this compile.
 pub struct Flags {
-    pub verbose: bool,
+    pub verbose: usize, // verbosity level: 0 == not verbose, 1 == verbose, 2 == very verbose
     pub stage: Option<u32>,
     pub keep_stage: Option<u32>,
     pub build: String,
@@ -37,6 +37,17 @@ pub struct Flags {
     pub src: Option<PathBuf>,
     pub jobs: Option<u32>,
     pub cmd: Subcommand,
+    pub incremental: bool,
+}
+
+impl Flags {
+    pub fn verbose(&self) -> bool {
+        self.verbose > 0
+    }
+
+    pub fn very_verbose(&self) -> bool {
+        self.verbose > 1
+    }
 }
 
 pub enum Subcommand {
@@ -63,7 +74,8 @@ pub enum Subcommand {
 impl Flags {
     pub fn parse(args: &[String]) -> Flags {
         let mut opts = Options::new();
-        opts.optflag("v", "verbose", "use verbose output");
+        opts.optflagmulti("v", "verbose", "use verbose output (-vv for very verbose)");
+        opts.optflag("i", "incremental", "use incremental compilation");
         opts.optopt("", "config", "TOML configuration file for build", "FILE");
         opts.optopt("", "build", "build target of the stage0 compiler", "BUILD");
         opts.optmulti("", "host", "host targets to build", "HOST");
@@ -256,8 +268,18 @@ To learn more about a subcommand, run `./x.py <command> -h`
             }
         });
 
+        let mut stage = m.opt_str("stage").map(|j| j.parse().unwrap());
+
+        let incremental = m.opt_present("i");
+
+        if incremental {
+            if stage.is_none() {
+                stage = Some(1);
+            }
+        }
+
         Flags {
-            verbose: m.opt_present("v"),
+            verbose: m.opt_count("v"),
             stage: m.opt_str("stage").map(|j| j.parse().unwrap()),
             keep_stage: m.opt_str("keep-stage").map(|j| j.parse().unwrap()),
             build: m.opt_str("build").unwrap_or_else(|| {
@@ -269,6 +291,7 @@ To learn more about a subcommand, run `./x.py <command> -h`
             src: m.opt_str("src").map(PathBuf::from),
             jobs: m.opt_str("jobs").map(|j| j.parse().unwrap()),
             cmd: cmd,
+            incremental: incremental,
         }
     }
 }