Auto merge of #6933 - ehuss:cache-output, r=alexcrichton

Add message caching.

The `cache-messages` feature causes Cargo to cache the messages generated by
the compiler. This is primarily useful if a crate compiles successfully with
warnings. Previously, re-running Cargo would not display any output. With the
`cache-messages` feature, it will quickly redisplay the previous warnings.

```
cargo +nightly check -Z cache-messages
```

Notes:
- `short` messages do not work correctly.
- rustdoc does not support `--json-rendered=termcolor`, so its output is currently uncolored.
- This approach to rendering should address some output issues like #6848.

Author: bors

.travis.yml

@@ -39,6 +39,7 @@ matrix:
 
 before_script:
   - rustup target add $ALT
+  - rustup component add clippy || echo "clippy not available"
 script:
   - cargo test --features=deny-warnings
 

Cargo.toml

@@ -54,6 +54,7 @@ serde = { version = "1.0.82", features = ['derive'] }
 serde_ignored = "0.0.4"
 serde_json = { version = "1.0.30", features = ["raw_value"] }
 shell-escape = "0.1.4"
+strip-ansi-escapes = "0.1.0"
 tar = { version = "0.4.18", default-features = false }
 tempfile = "3.0"
 termcolor = "1.0"

appveyor.yml

@@ -9,6 +9,7 @@ install:
   - rustup-init.exe -y --default-host x86_64-pc-windows-msvc --default-toolchain nightly
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - if defined OTHER_TARGET rustup target add %OTHER_TARGET%
+  - rustup component add clippy || exit 0
   - rustc -V
   - cargo -V
   - git submodule update --init

src/bin/cargo/cli.rs

@@ -35,6 +35,7 @@ Available unstable (nightly-only) flags:
     -Z unstable-options -- Allow the usage of unstable options such as --registry
     -Z config-profile   -- Read profiles from .cargo/config files
     -Z install-upgrade  -- `cargo install` will upgrade instead of failing
+    -Z cache-messages   -- Cache compiler messages
 
 Run with 'cargo -Z [FLAG] [SUBCOMMAND]'"
         );

src/cargo/core/compiler/build_config.rs

@@ -27,6 +27,8 @@ pub struct BuildConfig {
     /// An optional wrapper, if any, used to wrap rustc invocations
     pub rustc_wrapper: Option<ProcessBuilder>,
     pub rustfix_diagnostic_server: RefCell<Option<RustfixDiagnosticServer>>,
+    /// Whether or not Cargo should cache compiler output on disk.
+    cache_messages: bool,
 }
 
 impl BuildConfig {
@@ -87,6 +89,7 @@ impl BuildConfig {
         }
         let cfg_jobs: Option<u32> = config.get("build.jobs")?;
         let jobs = jobs.or(cfg_jobs).unwrap_or(::num_cpus::get() as u32);
+
         Ok(BuildConfig {
             requested_target: target,
             jobs,
@@ -97,10 +100,18 @@ impl BuildConfig {
             build_plan: false,
             rustc_wrapper: None,
             rustfix_diagnostic_server: RefCell::new(None),
+            cache_messages: config.cli_unstable().cache_messages,
         })
     }
 
-    pub fn json_messages(&self) -> bool {
+    /// Whether or not Cargo should cache compiler messages on disk.
+    pub fn cache_messages(&self) -> bool {
+        self.cache_messages
+    }
+
+    /// Whether or not the *user* wants JSON output. Whether or not rustc
+    /// actually uses JSON is decided in `add_error_format`.
+    pub fn emit_json(&self) -> bool {
         self.message_format == MessageFormat::Json
     }
 

src/cargo/core/compiler/context/compilation_files.rs

@@ -192,6 +192,11 @@ impl<'a, 'cfg: 'a> CompilationFiles<'a, 'cfg> {
         self.layout(unit.kind).fingerprint().join(dir)
     }
 
+    /// Path where compiler output is cached.
+    pub fn message_cache_path(&self, unit: &Unit<'a>) -> PathBuf {
+        self.fingerprint_dir(unit).join("output")
+    }
+
     /// Returns the directory where a compiled build script is stored.
     /// `/path/to/target/{debug,release}/build/PKG-HASH`
     pub fn build_script_dir(&self, unit: &Unit<'a>) -> PathBuf {

src/cargo/core/compiler/custom_build.rs

@@ -112,7 +112,7 @@ fn emit_build_output(state: &JobState<'_>, output: &BuildOutput, package_id: Pac
         env: &output.env,
     }
     .to_json_string();
-    state.stdout(&msg);
+    state.stdout(msg);
 }
 
 fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoResult<Job> {
@@ -248,7 +248,7 @@ fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoRes
     );
     let build_scripts = super::load_build_deps(cx, unit);
     let kind = unit.kind;
-    let json_messages = bcx.build_config.json_messages();
+    let json_messages = bcx.build_config.emit_json();
     let extra_verbose = bcx.config.extra_verbose();
     let (prev_output, prev_script_out_dir) = prev_build_output(cx, unit);
 
@@ -315,13 +315,13 @@ fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoRes
             .exec_with_streaming(
                 &mut |stdout| {
                     if extra_verbose {
-                        state.stdout(&format!("{}{}", prefix, stdout));
+                        state.stdout(format!("{}{}", prefix, stdout));
                     }
                     Ok(())
                 },
                 &mut |stderr| {
                     if extra_verbose {
-                        state.stderr(&format!("{}{}", prefix, stderr));
+                        state.stderr(format!("{}{}", prefix, stderr));
                     }
                     Ok(())
                 },

src/cargo/core/compiler/job_queue.rs

@@ -105,12 +105,12 @@ impl<'a> JobState<'a> {
             .send(Message::BuildPlanMsg(module_name, cmd, filenames));
     }
 
-    pub fn stdout(&self, stdout: &str) {
-        drop(self.tx.send(Message::Stdout(stdout.to_string())));
+    pub fn stdout(&self, stdout: String) {
+        drop(self.tx.send(Message::Stdout(stdout)));
     }
 
-    pub fn stderr(&self, stderr: &str) {
-        drop(self.tx.send(Message::Stderr(stderr.to_string())));
+    pub fn stderr(&self, stderr: String) {
+        drop(self.tx.send(Message::Stderr(stderr)));
     }
 
     /// A method used to signal to the coordinator thread that the rmeta file