cargo: build in Cargo's out dir if DENO_BUILD_PATH is not set

Plus some minor improvements and clean-ups:

* Resolve DENO_BUILD_PATH to an absolute path if necessary.
* Rename DENO_BUILD_PATH to GN_OUT_DIR in places where it is supposed to
  be set by the build system (and not a user configuration variable).
* Output Cargo `rerun-if-*-changed` instructions first, so even if the
  build itself fails, configuration changes will still trigger a re-run
  of build.rs.
* Remove TODOs that are impossible.
* Re-run build.rs when the flatbuffer definition file changes.

.appveyor.yml

@@ -8,15 +8,15 @@ clone_depth: 1
 
 environment:
  APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+ CARGO_HOME: $(USERPROFILE)\.cargo
+ CARGO_TARGET_DIR: $(APPVEYOR_BUILD_FOLDER)\target
  DENO_BUILD_MODE: release
  DENO_BUILD_PATH: $(APPVEYOR_BUILD_FOLDER)\out\release
  DENO_THIRD_PARTY_PATH: $(APPVEYOR_BUILD_FOLDER)\third_party
  MTIME_CACHE_DB: $(APPVEYOR_BUILD_FOLDER)\mtime_cache.xml
- CARGO_HOME: $(USERPROFILE)\.cargo
- CARGO_TARGET_DIR: $(APPVEYOR_BUILD_FOLDER)\out\target
+ RELEASE_ARTIFACT: deno_win_x64.zip
  RUSTUP_HOME: $(USERPROFILE)\.rustup
  RUST_BACKTRACE: 1
- RELEASE_ARTIFACT: deno_win_x64.zip
 
  # Appveyor uses 7zip to pack cache directories. We use these options:
  # -t7z : Use '7z' format.
@@ -234,6 +234,7 @@ cache:
  # Cache file mtimes in the main git repo, also to enable incremental builds.
  - $(MTIME_CACHE_DB)
  # Build incrementally.
+ - $(CARGO_TARGET_DIR)
  - $(DENO_BUILD_PATH)
 
 init:
@@ -319,6 +320,7 @@ install:
 before_build:
  # Mark all files in the build dir 'not needed' until proven otherwise.
  # TODO: also track files in third_party that aren't checked into the repo.
+ # TODO: also track files in $CARGO_TARGET_DIR.
  - ps: Start-TraceFilesNeeded $env:DENO_BUILD_PATH -Recurse
 
  # Download clang and gn, generate ninja files.

.travis.yml

@@ -14,7 +14,7 @@ env:
  - HOMEBREW_PATH=$HOME/homebrew/
  - DENO_BUILD_ARGS="use_custom_libcxx=false use_sysroot=false"
  - DENO_BUILD_PATH=$HOME/out/Default
- - CARGO_TARGET_DIR=$DENO_BUILD_PATH
+ - CARGO_TARGET_DIR=$HOME/target
  - DENO_BUILD_MODE=release
  - PATH=$TRAVIS_BUILD_DIR/third_party/llvm-build/Release+Asserts/bin:$CARGO_HOME/bin:$PATH
  - CCACHE_CPP2=yes

build.rs

@@ -1,18 +1,37 @@
 // Copyright 2018 the Deno authors. All rights reserved. MIT license.
 
 // Run "cargo build -vv" if you want to see gn output.
-// TODO For the time being you must set an env var DENO_BUILD_PATH
-// which might be `pwd`/out/debug or `pwd`/out/release.
-// TODO Currently DENO_BUILD_PATH must be absolute.
-// TODO Combine DENO_BUILD_PATH and OUT_DIR.
+
+#![deny(warnings)]
 
 use std::env;
-use std::path::PathBuf;
+use std::path::{self, Path, PathBuf};
 use std::process::Command;
 
 fn main() {
+ // Cargo sets PROFILE to either "debug" or "release", which conveniently
+ // matches the build modes we support.
  let mode = env::var("PROFILE").unwrap();
- let deno_build_path = env::var("DENO_BUILD_PATH").unwrap();
+
+ // Normally we configure GN+Ninja to build into Cargo's OUT_DIR.
+ // However, when DENO_BUILD_PATH is set, perform the ninja build in that dir
+ // instead. This is used by CI to avoid building V8 etc twice.
+ let out_dir = env::var_os("OUT_DIR").unwrap();
+ let gn_out_dir = match env::var_os("DENO_BUILD_PATH") {
+ None => abs_path(out_dir),
+ Some(deno_build_path) => abs_path(deno_build_path),
+ };
+
+ // Give cargo some instructions. We do this first so the `rerun-if-*-changed`
+ // directives can take effect even if something the build itself fails.
+ println!("cargo:rustc-env=GN_OUT_DIR={}", gn_out_dir);
+ println!("cargo:rustc-link-search=native={}/obj", gn_out_dir);
+ println!("cargo:rustc-link-lib=static=deno_deps");
+
+ println!("cargo:rerun-if-changed={}", abs_path("src/msg.fbs"));
+ println!("cargo:rerun-if-env-changed=DENO_BUILD_PATH");
+ // TODO: this is obviously not appropriate here.
+ println!("cargo:rerun-if-env-changed=APPVEYOR_REPO_COMMIT");
 
  // Detect if we're being invoked by the rust language server (RLS).
  // Unfortunately we can't detect whether we're being run by `cargo check`.
@@ -33,21 +52,15 @@ fn main() {
  };
 
  let status = Command::new("python")
- .env("DENO_BUILD_PATH", &deno_build_path)
+ .env("DENO_BUILD_PATH", &gn_out_dir)
  .env("DENO_BUILD_MODE", &mode)
  .arg("./tools/setup.py")
  .status()
  .expect("setup.py failed");
  assert!(status.success());
 
- // These configurations must be outputted after tools/setup.py is run.
- println!("cargo:rustc-link-search=native={}/obj", deno_build_path);
- println!("cargo:rustc-link-lib=static=deno_deps");
- // TODO Remove this and only use OUT_DIR at some point.
- println!("cargo:rustc-env=DENO_BUILD_PATH={}", deno_build_path);
-
  let status = Command::new("python")
- .env("DENO_BUILD_PATH", &deno_build_path)
+ .env("DENO_BUILD_PATH", &gn_out_dir)
  .env("DENO_BUILD_MODE", &mode)
  .arg("./tools/build.py")
  .arg(gn_target)
@@ -56,3 +69,17 @@ fn main() {
  .expect("build.py failed");
  assert!(status.success());
 }
+
+// Utility function to make a path absolute, normalizing it to use forward
+// slashes only. The returned value is an owned String, otherwise panics.
+fn abs_path<P: AsRef<Path>>(path: P) -> String {
+ env::current_dir()
+ .unwrap()
+ .join(path)
+ .to_str()
+ .unwrap()
+ .to_owned()
+ .chars()
+ .map(|c| if path::is_separator(c) { '/' } else { c })
+ .collect()
+}