Auto merge of #5432 - djc:split-context, r=alexcrichton

Split Context into two types

@matklad here's the crazy attempt to make the `Context` situation slightly more sane. It basically splits all of the stuff that is immutable over the lifetime of the compilation from the stuff that's initialized empty. The latter is now stored in a type which I have provisionally called `BuildProgress` -- feel free to bikeshed about the name (I came up with `BuildData` as another alternative). It stores a reference to the `Context` to make things easier for now, we might want to change that down the line.

IMO this is a pretty good improvement, which clarifies the design quite a bit.

@alexcrichton you'll probably want to review this, too.

src/cargo/core/compiler/build_context/mod.rs

@@ -0,0 +1,323 @@
+use std::env;
+use std::path::Path;
+use std::str::{self, FromStr};
+
+use core::profiles::Profiles;
+use core::{Dependency, Workspace};
+use core::{Package, PackageId, PackageSet, Resolve};
+use util::errors::CargoResult;
+use util::{profile, Cfg, CfgExpr, Config};
+
+use super::{BuildConfig, Kind, TargetConfig, Unit};
+
+mod target_info;
+pub use self::target_info::{FileFlavor, TargetInfo};
+
+/// The build context, containing all information about a build task
+pub struct BuildContext<'a, 'cfg: 'a> {
+    /// The workspace the build is for
+    pub ws: &'a Workspace<'cfg>,
+    /// The cargo configuration
+    pub config: &'cfg Config,
+    /// The dependency graph for our build
+    pub resolve: &'a Resolve,
+    pub profiles: &'a Profiles,
+    pub build_config: &'a BuildConfig,
+    /// This is a workaround to carry the extra compiler args for either
+    /// `rustc` or `rustdoc` given on the command-line for the commands `cargo
+    /// rustc` and `cargo rustdoc`.  These commands only support one target,
+    /// but we don't want the args passed to any dependencies, so we include
+    /// the `Unit` corresponding to the top-level target.
+    pub extra_compiler_args: Option<(Unit<'a>, Vec<String>)>,
+    pub packages: &'a PackageSet<'cfg>,
+
+    pub target_info: TargetInfo,
+    pub host_info: TargetInfo,
+    pub incremental_env: Option<bool>,
+}
+
+impl<'a, 'cfg> BuildContext<'a, 'cfg> {
+    pub fn new(
+        ws: &'a Workspace<'cfg>,
+        resolve: &'a Resolve,
+        packages: &'a PackageSet<'cfg>,
+        config: &'cfg Config,
+        build_config: &'a BuildConfig,
+        profiles: &'a Profiles,
+        extra_compiler_args: Option<(Unit<'a>, Vec<String>)>,
+    ) -> CargoResult<BuildContext<'a, 'cfg>> {
+        let incremental_env = match env::var("CARGO_INCREMENTAL") {
+            Ok(v) => Some(v == "1"),
+            Err(_) => None,
+        };
+
+        let (host_info, target_info) = {
+            let _p = profile::start("BuildContext::probe_target_info");
+            debug!("probe_target_info");
+            let host_info = TargetInfo::new(config, &build_config, Kind::Host)?;
+            let target_info = TargetInfo::new(config, &build_config, Kind::Target)?;
+            (host_info, target_info)
+        };
+
+        Ok(BuildContext {
+            ws,
+            resolve,
+            packages,
+            config,
+            target_info,
+            host_info,
+            build_config,
+            profiles,
+            incremental_env,
+            extra_compiler_args,
+        })
+    }
+
+    pub fn extern_crate_name(&self, unit: &Unit<'a>, dep: &Unit<'a>) -> CargoResult<String> {
+        let deps = {
+            let a = unit.pkg.package_id();
+            let b = dep.pkg.package_id();
+            if a == b {
+                &[]
+            } else {
+                self.resolve.dependencies_listed(a, b)
+            }
+        };
+
+        let crate_name = dep.target.crate_name();
+        let mut names = deps.iter()
+            .map(|d| d.rename().unwrap_or(&crate_name));
+        let name = names.next().unwrap_or(&crate_name);
+        for n in names {
+            if n == name {
+                continue
+            }
+            bail!("multiple dependencies listed for the same crate must \
+                   all have the same name, but the dependency on `{}` \
+                   is listed as having different names", dep.pkg.package_id());
+        }
+        Ok(name.to_string())
+    }
+
+    /// Whether a dependency should be compiled for the host or target platform,
+    /// specified by `Kind`.
+    pub fn dep_platform_activated(&self, dep: &Dependency, kind: Kind) -> bool {
+        // If this dependency is only available for certain platforms,
+        // make sure we're only enabling it for that platform.
+        let platform = match dep.platform() {
+            Some(p) => p,
+            None => return true,
+        };
+        let (name, info) = match kind {
+            Kind::Host => (self.build_config.host_triple(), &self.host_info),
+            Kind::Target => (self.build_config.target_triple(), &self.target_info),
+        };
+        platform.matches(name, info.cfg())
+    }
+
+    /// Gets a package for the given package id.
+    pub fn get_package(&self, id: &PackageId) -> CargoResult<&'a Package> {
+        self.packages.get(id)
+    }
+
+    /// Get the user-specified linker for a particular host or target
+    pub fn linker(&self, kind: Kind) -> Option<&Path> {
+        self.target_config(kind).linker.as_ref().map(|s| s.as_ref())
+    }
+
+    /// Get the user-specified `ar` program for a particular host or target
+    pub fn ar(&self, kind: Kind) -> Option<&Path> {
+        self.target_config(kind).ar.as_ref().map(|s| s.as_ref())
+    }
+
+    /// Get the list of cfg printed out from the compiler for the specified kind
+    pub fn cfg(&self, kind: Kind) -> &[Cfg] {
+        let info = match kind {
+            Kind::Host => &self.host_info,
+            Kind::Target => &self.target_info,
+        };
+        info.cfg().unwrap_or(&[])
+    }
+
+    /// Get the target configuration for a particular host or target
+    fn target_config(&self, kind: Kind) -> &TargetConfig {
+        match kind {
+            Kind::Host => &self.build_config.host,
+            Kind::Target => &self.build_config.target,
+        }
+    }
+
+    /// Number of jobs specified for this build
+    pub fn jobs(&self) -> u32 {
+        self.build_config.jobs
+    }
+
+    pub fn rustflags_args(&self, unit: &Unit) -> CargoResult<Vec<String>> {
+        env_args(
+            self.config,
+            &self.build_config,
+            self.info(&unit.kind).cfg(),
+            unit.kind,
+            "RUSTFLAGS",
+        )
+    }
+
+    pub fn rustdocflags_args(&self, unit: &Unit) -> CargoResult<Vec<String>> {
+        env_args(
+            self.config,
+            &self.build_config,
+            self.info(&unit.kind).cfg(),
+            unit.kind,
+            "RUSTDOCFLAGS",
+        )
+    }
+
+    pub fn show_warnings(&self, pkg: &PackageId) -> bool {
+        pkg.source_id().is_path() || self.config.extra_verbose()
+    }
+
+    fn info(&self, kind: &Kind) -> &TargetInfo {
+        match *kind {
+            Kind::Host => &self.host_info,
+            Kind::Target => &self.target_info,
+        }
+    }
+
+    pub fn extra_args_for(&self, unit: &Unit<'a>) -> Option<&Vec<String>> {
+        if let Some((ref args_unit, ref args)) = self.extra_compiler_args {
+            if args_unit == unit {
+                return Some(args);
+            }
+        }
+        None
+    }
+}
+
+/// Acquire extra flags to pass to the compiler from various locations.
+///
+/// The locations are:
+///
+///  - the `RUSTFLAGS` environment variable
+///
+/// then if this was not found
+///
+///  - `target.*.rustflags` from the manifest (Cargo.toml)
+///  - `target.cfg(..).rustflags` from the manifest
+///
+/// then if neither of these were found
+///
+///  - `build.rustflags` from the manifest
+///
+/// Note that if a `target` is specified, no args will be passed to host code (plugins, build
+/// scripts, ...), even if it is the same as the target.
+fn env_args(
+    config: &Config,
+    build_config: &BuildConfig,
+    target_cfg: Option<&[Cfg]>,
+    kind: Kind,
+    name: &str,
+) -> CargoResult<Vec<String>> {
+    // We *want* to apply RUSTFLAGS only to builds for the
+    // requested target architecture, and not to things like build
+    // scripts and plugins, which may be for an entirely different
+    // architecture. Cargo's present architecture makes it quite
+    // hard to only apply flags to things that are not build
+    // scripts and plugins though, so we do something more hacky
+    // instead to avoid applying the same RUSTFLAGS to multiple targets
+    // arches:
+    //
+    // 1) If --target is not specified we just apply RUSTFLAGS to
+    // all builds; they are all going to have the same target.
+    //
+    // 2) If --target *is* specified then we only apply RUSTFLAGS
+    // to compilation units with the Target kind, which indicates
+    // it was chosen by the --target flag.
+    //
+    // This means that, e.g. even if the specified --target is the
+    // same as the host, build scripts in plugins won't get
+    // RUSTFLAGS.
+    let compiling_with_target = build_config.requested_target.is_some();
+    let is_target_kind = kind == Kind::Target;
+
+    if compiling_with_target && !is_target_kind {
+        // This is probably a build script or plugin and we're
+        // compiling with --target. In this scenario there are
+        // no rustflags we can apply.
+        return Ok(Vec::new());
+    }
+
+    // First try RUSTFLAGS from the environment
+    if let Ok(a) = env::var(name) {
+        let args = a.split(' ')
+            .map(str::trim)
+            .filter(|s| !s.is_empty())
+            .map(str::to_string);
+        return Ok(args.collect());
+    }
+
+    let mut rustflags = Vec::new();
+
+    let name = name.chars()
+        .flat_map(|c| c.to_lowercase())
+        .collect::<String>();
+    // Then the target.*.rustflags value...
+    let target = build_config
+        .requested_target
+        .as_ref()
+        .map(|s| s.as_str())
+        .unwrap_or(build_config.host_triple());
+    let key = format!("target.{}.{}", target, name);
+    if let Some(args) = config.get_list_or_split_string(&key)? {
+        let args = args.val.into_iter();
+        rustflags.extend(args);
+    }
+    // ...including target.'cfg(...)'.rustflags
+    if let Some(target_cfg) = target_cfg {
+        if let Some(table) = config.get_table("target")? {
+            let cfgs = table.val.keys().filter_map(|t| {
+                if t.starts_with("cfg(") && t.ends_with(')') {
+                    let cfg = &t[4..t.len() - 1];
+                    CfgExpr::from_str(cfg).ok().and_then(|c| {
+                        if c.matches(target_cfg) {
+                            Some(t)
+                        } else {
+                            None
+                        }
+                    })
+                } else {
+                    None
+                }
+            });
+
+            // Note that we may have multiple matching `[target]` sections and
+            // because we're passing flags to the compiler this can affect
+            // cargo's caching and whether it rebuilds. Ensure a deterministic
+            // ordering through sorting for now. We may perhaps one day wish to
+            // ensure a deterministic ordering via the order keys were defined
+            // in files perhaps.
+            let mut cfgs = cfgs.collect::<Vec<_>>();
+            cfgs.sort();
+
+            for n in cfgs {
+                let key = format!("target.{}.{}", n, name);
+                if let Some(args) = config.get_list_or_split_string(&key)? {
+                    let args = args.val.into_iter();
+                    rustflags.extend(args);
+                }
+            }
+        }
+    }
+
+    if !rustflags.is_empty() {
+        return Ok(rustflags);
+    }
+
+    // Then the build.rustflags value
+    let key = format!("build.{}", name);
+    if let Some(args) = config.get_list_or_split_string(&key)? {
+        let args = args.val.into_iter();
+        return Ok(args.collect());
+    }
+
+    Ok(Vec::new())
+}

src/cargo/core/compiler/compilation.rs

@@ -175,7 +175,7 @@ impl<'cfg> Compilation<'cfg> {
         // When adding new environment variables depending on
         // crate properties which might require rebuild upon change
         // consider adding the corresponding properties to the hash
-        // in Context::target_metadata()
+        // in BuildContext::target_metadata()
         cmd.env("CARGO_MANIFEST_DIR", pkg.root())
             .env("CARGO_PKG_VERSION_MAJOR", &pkg.version().major.to_string())
             .env("CARGO_PKG_VERSION_MINOR", &pkg.version().minor.to_string())