rust/src/librustc/session/mod.rs

// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

pub use self::code_stats::{CodeStats, DataTypeKind, FieldInfo};
pub use self::code_stats::{SizeKind, TypeSizeInfo, VariantInfo};

use dep_graph::DepGraph;
use hir::def_id::{CrateNum, DefIndex};

use lint;
use middle::cstore::CrateStore;
use middle::allocator::AllocatorKind;
use middle::dependency_format;
use session::search_paths::PathKind;
use session::config::DebugInfoLevel;
use ty::tls;
use util::nodemap::{FxHashMap, FxHashSet};
use util::common::{duration_to_secs_str, ErrorReported};

use syntax::ast::NodeId;
use errors::{self, DiagnosticBuilder};
use errors::emitter::{Emitter, EmitterWriter};
use syntax::json::JsonEmitter;
use syntax::feature_gate;
use syntax::parse;
use syntax::parse::ParseSess;
use syntax::symbol::Symbol;
use syntax::{ast, codemap};
use syntax::feature_gate::AttributeType;
use syntax_pos::{Span, MultiSpan};

use rustc_back::{LinkerFlavor, PanicStrategy};
use rustc_back::target::Target;
use rustc_data_structures::flock;
use jobserver::Client;

use std::cell::{self, Cell, RefCell};
use std::collections::HashMap;
use std::env;
use std::fmt;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::rc::Rc;
use std::sync::{Once, ONCE_INIT};
use std::time::Duration;

mod code_stats;
pub mod config;
pub mod filesearch;
pub mod search_paths;

// Represents the data associated with a compilation
// session for a single crate.
pub struct Session {
    pub dep_graph: DepGraph,
    pub target: config::Config,
    pub host: Target,
    pub opts: config::Options,
    pub cstore: Rc<CrateStore>,
    pub parse_sess: ParseSess,
    // For a library crate, this is always none
    pub entry_fn: RefCell<Option<(NodeId, Span)>>,
    pub entry_type: Cell<Option<config::EntryFnType>>,
    pub plugin_registrar_fn: Cell<Option<ast::NodeId>>,
    pub derive_registrar_fn: Cell<Option<ast::NodeId>>,
    pub default_sysroot: Option<PathBuf>,
    // The name of the root source file of the crate, in the local file system.
    // The path is always expected to be absolute. `None` means that there is no
    // source file.
    pub local_crate_source_file: Option<String>,
    // The directory the compiler has been executed in plus a flag indicating
    // if the value stored here has been affected by path remapping.
    pub working_dir: (String, bool),
    pub lint_store: RefCell<lint::LintStore>,
    pub lints: RefCell<lint::LintTable>,
    /// Set of (LintId, Option<Span>, message) tuples tracking lint
    /// (sub)diagnostics that have been set once, but should not be set again,
    /// in order to avoid redundantly verbose output (Issue #24690).
    pub one_time_diagnostics: RefCell<FxHashSet<(lint::LintId, Option<Span>, String)>>,
    pub plugin_llvm_passes: RefCell<Vec<String>>,
    pub plugin_attributes: RefCell<Vec<(String, AttributeType)>>,
    pub crate_types: RefCell<Vec<config::CrateType>>,
    pub dependency_formats: RefCell<dependency_format::Dependencies>,
    // The crate_disambiguator is constructed out of all the `-C metadata`
    // arguments passed to the compiler. Its value together with the crate-name
    // forms a unique global identifier for the crate. It is used to allow
    // multiple crates with the same name to coexist. See the
    // trans::back::symbol_names module for more information.
    pub crate_disambiguator: RefCell<Symbol>,
    pub features: RefCell<feature_gate::Features>,

    /// The maximum recursion limit for potentially infinitely recursive
    /// operations such as auto-dereference and monomorphization.
    pub recursion_limit: Cell<usize>,

    /// The maximum length of types during monomorphization.
    pub type_length_limit: Cell<usize>,

    /// The metadata::creader module may inject an allocator/panic_runtime
    /// dependency if it didn't already find one, and this tracks what was
    /// injected.
    pub injected_allocator: Cell<Option<CrateNum>>,
    pub allocator_kind: Cell<Option<AllocatorKind>>,
    pub injected_panic_runtime: Cell<Option<CrateNum>>,

    /// Map from imported macro spans (which consist of
    /// the localized span for the macro body) to the
    /// macro name and defintion span in the source crate.
    pub imported_macro_spans: RefCell<HashMap<Span, (String, Span)>>,

    incr_comp_session: RefCell<IncrCompSession>,

    /// Some measurements that are being gathered during compilation.
    pub perf_stats: PerfStats,

    /// Data about code being compiled, gathered during compilation.
    pub code_stats: RefCell<CodeStats>,

    next_node_id: Cell<ast::NodeId>,

    /// If -zfuel=crate=n is specified, Some(crate).
    optimization_fuel_crate: Option<String>,
    /// If -zfuel=crate=n is specified, initially set to n. Otherwise 0.
    optimization_fuel_limit: Cell<u64>,
    /// We're rejecting all further optimizations.
    out_of_fuel: Cell<bool>,

    // The next two are public because the driver needs to read them.

    /// If -zprint-fuel=crate, Some(crate).
    pub print_fuel_crate: Option<String>,
    /// Always set to zero and incremented so that we can print fuel expended by a crate.
    pub print_fuel: Cell<u64>,

    /// Loaded up early on in the initialization of this `Session` to avoid
    /// false positives about a job server in our environment.
    pub jobserver_from_env: Option<Client>,

    /// Metadata about the allocators for the current crate being compiled
    pub has_global_allocator: Cell<bool>,
}

pub struct PerfStats {
    // The accumulated time needed for computing the SVH of the crate
    pub svh_time: Cell<Duration>,
    // The accumulated time spent on computing incr. comp. hashes
    pub incr_comp_hashes_time: Cell<Duration>,
    // The number of incr. comp. hash computations performed
    pub incr_comp_hashes_count: Cell<u64>,
    // The number of bytes hashed when computing ICH values
    pub incr_comp_bytes_hashed: Cell<u64>,
    // The accumulated time spent on computing symbol hashes
    pub symbol_hash_time: Cell<Duration>,
    // The accumulated time spent decoding def path tables from metadata
    pub decode_def_path_tables_time: Cell<Duration>,
}

/// Enum to support dispatch of one-time diagnostics (in Session.diag_once)
enum DiagnosticBuilderMethod {
    Note,
    SpanNote,
    // add more variants as needed to support one-time diagnostics
}

impl Session {
    pub fn local_crate_disambiguator(&self) -> Symbol {
        *self.crate_disambiguator.borrow()
    }
    pub fn struct_span_warn<'a, S: Into<MultiSpan>>(&'a self,
                                                    sp: S,
                                                    msg: &str)
                                                    -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_warn(sp, msg)
    }
    pub fn struct_span_warn_with_code<'a, S: Into<MultiSpan>>(&'a self,
                                                              sp: S,
                                                              msg: &str,
                                                              code: &str)
                                                              -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_warn_with_code(sp, msg, code)
    }
    pub fn struct_warn<'a>(&'a self, msg: &str) -> DiagnosticBuilder<'a>  {
        self.diagnostic().struct_warn(msg)
    }
    pub fn struct_span_err<'a, S: Into<MultiSpan>>(&'a self,
                                                   sp: S,
                                                   msg: &str)
                                                   -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_err(sp, msg)
    }
    pub fn struct_span_err_with_code<'a, S: Into<MultiSpan>>(&'a self,
                                                             sp: S,
                                                             msg: &str,
                                                             code: &str)
                                                             -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_err_with_code(sp, msg, code)
    }
    // FIXME: This method should be removed (every error should have an associated error code).
    pub fn struct_err<'a>(&'a self, msg: &str) -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_err(msg)
    }
    pub fn struct_err_with_code<'a>(&'a self, msg: &str, code: &str) -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_err_with_code(msg, code)
    }
    pub fn struct_span_fatal<'a, S: Into<MultiSpan>>(&'a self,
                                                     sp: S,
                                                     msg: &str)
                                                     -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_fatal(sp, msg)
    }
    pub fn struct_span_fatal_with_code<'a, S: Into<MultiSpan>>(&'a self,
                                                               sp: S,
                                                               msg: &str,
                                                               code: &str)
                                                               -> DiagnosticBuilder<'a> {
        self.diagnostic().struct_span_fatal_with_code(sp, msg, code)
    }
    pub fn struct_fatal<'a>(&'a self, msg: &str) -> DiagnosticBuilder<'a>  {
        self.diagnostic().struct_fatal(msg)
    }

    pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
        panic!(self.diagnostic().span_fatal(sp, msg))
    }
    pub fn span_fatal_with_code<S: Into<MultiSpan>>(&self, sp: S, msg: &str, code: &str) -> ! {
        panic!(self.diagnostic().span_fatal_with_code(sp, msg, code))
    }
    pub fn fatal(&self, msg: &str) -> ! {
        panic!(self.diagnostic().fatal(msg))
    }
    pub fn span_err_or_warn<S: Into<MultiSpan>>(&self, is_warning: bool, sp: S, msg: &str) {
        if is_warning {
            self.span_warn(sp, msg);
        } else {
            self.span_err(sp, msg);
        }
    }
    pub fn span_err<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
        self.diagnostic().span_err(sp, msg)
    }
    pub fn span_err_with_code<S: Into<MultiSpan>>(&self, sp: S, msg: &str, code: &str) {
        self.diagnostic().span_err_with_code(sp, &msg, code)
    }
    pub fn err(&self, msg: &str) {
        self.diagnostic().err(msg)
    }
    pub fn err_count(&self) -> usize {
        self.diagnostic().err_count()
    }
    pub fn has_errors(&self) -> bool {
        self.diagnostic().has_errors()
    }
    pub fn abort_if_errors(&self) {
        self.diagnostic().abort_if_errors();
    }
    pub fn compile_status(&self) -> Result<(), CompileIncomplete> {
        compile_result_from_err_count(self.err_count())
    }
    pub fn track_errors<F, T>(&self, f: F) -> Result<T, ErrorReported>
        where F: FnOnce() -> T
    {
        let old_count = self.err_count();
        let result = f();
        let errors = self.err_count() - old_count;
        if errors == 0 {
            Ok(result)
        } else {
            Err(ErrorReported)
        }
    }
    pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
        self.diagnostic().span_warn(sp, msg)
    }
    pub fn span_warn_with_code<S: Into<MultiSpan>>(&self, sp: S, msg: &str, code: &str) {
        self.diagnostic().span_warn_with_code(sp, msg, code)
    }
    pub fn warn(&self, msg: &str) {
        self.diagnostic().warn(msg)
    }
    pub fn opt_span_warn<S: Into<MultiSpan>>(&self, opt_sp: Option<S>, msg: &str) {
        match opt_sp {
            Some(sp) => self.span_warn(sp, msg),
            None => self.warn(msg),
        }
    }
    /// Delay a span_bug() call until abort_if_errors()
    pub fn delay_span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
        self.diagnostic().delay_span_bug(sp, msg)
    }
    pub fn note_without_error(&self, msg: &str) {
        self.diagnostic().note_without_error(msg)
    }
    pub fn span_note_without_error<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
        self.diagnostic().span_note_without_error(sp, msg)
    }
    pub fn span_unimpl<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
        self.diagnostic().span_unimpl(sp, msg)
    }
    pub fn unimpl(&self, msg: &str) -> ! {
        self.diagnostic().unimpl(msg)
    }

    pub fn add_lint<S: Into<MultiSpan>>(&self,
                                        lint: &'static lint::Lint,
                                        id: ast::NodeId,
                                        sp: S,
                                        msg: String)
    {
        self.lints.borrow_mut().add_lint(lint, id, sp, msg);
    }

    pub fn add_lint_diagnostic<M>(&self,
                                  lint: &'static lint::Lint,
                                  id: ast::NodeId,
                                  msg: M)
        where M: lint::IntoEarlyLint,
    {
        self.lints.borrow_mut().add_lint_diagnostic(lint, id, msg);
    }

    pub fn reserve_node_ids(&self, count: usize) -> ast::NodeId {
        let id = self.next_node_id.get();

        match id.as_usize().checked_add(count) {
            Some(next) => {
                self.next_node_id.set(ast::NodeId::new(next));
            }
            None => bug!("Input too large, ran out of node ids!")
        }

        id
    }
    pub fn next_node_id(&self) -> NodeId {
        self.reserve_node_ids(1)
    }
    pub fn diagnostic<'a>(&'a self) -> &'a errors::Handler {
        &self.parse_sess.span_diagnostic
    }

    /// Analogous to calling methods on the given `DiagnosticBuilder`, but
    /// deduplicates on lint ID, span (if any), and message for this `Session`
    /// if we're not outputting in JSON mode.
    fn diag_once<'a, 'b>(&'a self,
                         diag_builder: &'b mut DiagnosticBuilder<'a>,
                         method: DiagnosticBuilderMethod,
                         lint: &'static lint::Lint, message: &str, span: Option<Span>) {
        let mut do_method = || {
            match method {
                DiagnosticBuilderMethod::Note => {
                    diag_builder.note(message);
                },
                DiagnosticBuilderMethod::SpanNote => {
                    diag_builder.span_note(span.expect("span_note expects a span"), message);
                }
            }
        };

        match self.opts.error_format {
            // when outputting JSON for tool consumption, the tool might want
            // the duplicates
            config::ErrorOutputType::Json => {
                do_method()
            },
            _ => {
                let lint_id = lint::LintId::of(lint);
                let id_span_message = (lint_id, span, message.to_owned());
                let fresh = self.one_time_diagnostics.borrow_mut().insert(id_span_message);
                if fresh {
                    do_method()
                }
            }
        }
    }

    pub fn diag_span_note_once<'a, 'b>(&'a self,
                                       diag_builder: &'b mut DiagnosticBuilder<'a>,
                                       lint: &'static lint::Lint, span: Span, message: &str) {
        self.diag_once(diag_builder, DiagnosticBuilderMethod::SpanNote, lint, message, Some(span));
    }

    pub fn diag_note_once<'a, 'b>(&'a self,
                                  diag_builder: &'b mut DiagnosticBuilder<'a>,
                                  lint: &'static lint::Lint, message: &str) {
        self.diag_once(diag_builder, DiagnosticBuilderMethod::Note, lint, message, None);
    }

    pub fn codemap<'a>(&'a self) -> &'a codemap::CodeMap {
        self.parse_sess.codemap()
    }
    pub fn verbose(&self) -> bool { self.opts.debugging_opts.verbose }
    pub fn time_passes(&self) -> bool { self.opts.debugging_opts.time_passes }
    pub fn count_llvm_insns(&self) -> bool {
        self.opts.debugging_opts.count_llvm_insns
    }
    pub fn time_llvm_passes(&self) -> bool {
        self.opts.debugging_opts.time_llvm_passes
    }
    pub fn trans_stats(&self) -> bool { self.opts.debugging_opts.trans_stats }
    pub fn meta_stats(&self) -> bool { self.opts.debugging_opts.meta_stats }
    pub fn asm_comments(&self) -> bool { self.opts.debugging_opts.asm_comments }
    pub fn no_verify(&self) -> bool { self.opts.debugging_opts.no_verify }
    pub fn borrowck_stats(&self) -> bool { self.opts.debugging_opts.borrowck_stats }
    pub fn print_llvm_passes(&self) -> bool {
        self.opts.debugging_opts.print_llvm_passes
    }
    pub fn lto(&self) -> bool {
        self.opts.cg.lto
    }
    /// Returns the panic strategy for this compile session. If the user explicitly selected one
    /// using '-C panic', use that, otherwise use the panic strategy defined by the target.
    pub fn panic_strategy(&self) -> PanicStrategy {
        self.opts.cg.panic.unwrap_or(self.target.target.options.panic_strategy)
    }
    pub fn linker_flavor(&self) -> LinkerFlavor {
        self.opts.debugging_opts.linker_flavor.unwrap_or(self.target.target.linker_flavor)
    }
    pub fn no_landing_pads(&self) -> bool {
        self.opts.debugging_opts.no_landing_pads || self.panic_strategy() == PanicStrategy::Abort
    }
    pub fn unstable_options(&self) -> bool {
        self.opts.debugging_opts.unstable_options
    }
    pub fn nonzeroing_move_hints(&self) -> bool {
        self.opts.debugging_opts.enable_nonzeroing_move_hints
    }
    pub fn overflow_checks(&self) -> bool {
        self.opts.cg.overflow_checks
            .or(self.opts.debugging_opts.force_overflow_checks)
            .unwrap_or(self.opts.debug_assertions)
    }

    pub fn must_not_eliminate_frame_pointers(&self) -> bool {
        self.opts.debuginfo != DebugInfoLevel::NoDebugInfo ||
        !self.target.target.options.eliminate_frame_pointer
    }

    /// Returns the symbol name for the registrar function,
    /// given the crate Svh and the function DefIndex.
    pub fn generate_plugin_registrar_symbol(&self, disambiguator: Symbol, index: DefIndex)
                                            -> String {
        format!("__rustc_plugin_registrar__{}_{}", disambiguator, index.as_usize())
    }

    pub fn generate_derive_registrar_symbol(&self, disambiguator: Symbol, index: DefIndex)
                                            -> String {
        format!("__rustc_derive_registrar__{}_{}", disambiguator, index.as_usize())
    }

    pub fn sysroot<'a>(&'a self) -> &'a Path {
        match self.opts.maybe_sysroot {
            Some (ref sysroot) => sysroot,
            None => self.default_sysroot.as_ref()
                        .expect("missing sysroot and default_sysroot in Session")
        }
    }
    pub fn target_filesearch(&self, kind: PathKind) -> filesearch::FileSearch {
        filesearch::FileSearch::new(self.sysroot(),
                                    &self.opts.target_triple,
                                    &self.opts.search_paths,
                                    kind)
    }
    pub fn host_filesearch(&self, kind: PathKind) -> filesearch::FileSearch {
        filesearch::FileSearch::new(
            self.sysroot(),
            config::host_triple(),
            &self.opts.search_paths,
            kind)
    }

    pub fn init_incr_comp_session(&self,
                                  session_dir: PathBuf,
                                  lock_file: flock::Lock) {
        let mut incr_comp_session = self.incr_comp_session.borrow_mut();

        if let IncrCompSession::NotInitialized = *incr_comp_session { } else {
            bug!("Trying to initialize IncrCompSession `{:?}`", *incr_comp_session)
        }

        *incr_comp_session = IncrCompSession::Active {
            session_directory: session_dir,
            lock_file: lock_file,
        };
    }

    pub fn finalize_incr_comp_session(&self, new_directory_path: PathBuf) {
        let mut incr_comp_session = self.incr_comp_session.borrow_mut();

        if let IncrCompSession::Active { .. } = *incr_comp_session { } else {
            bug!("Trying to finalize IncrCompSession `{:?}`", *incr_comp_session)
        }

        // Note: This will also drop the lock file, thus unlocking the directory
        *incr_comp_session = IncrCompSession::Finalized {
            session_directory: new_directory_path,
        };
    }

    pub fn mark_incr_comp_session_as_invalid(&self) {
        let mut incr_comp_session = self.incr_comp_session.borrow_mut();

        let session_directory = match *incr_comp_session {
            IncrCompSession::Active { ref session_directory, .. } => {
                session_directory.clone()
            }
            _ => bug!("Trying to invalidate IncrCompSession `{:?}`",
                      *incr_comp_session),
        };

        // Note: This will also drop the lock file, thus unlocking the directory
        *incr_comp_session = IncrCompSession::InvalidBecauseOfErrors {
            session_directory: session_directory
        };
    }

    pub fn incr_comp_session_dir(&self) -> cell::Ref<PathBuf> {
        let incr_comp_session = self.incr_comp_session.borrow();
        cell::Ref::map(incr_comp_session, |incr_comp_session| {
            match *incr_comp_session {
                IncrCompSession::NotInitialized => {
                    bug!("Trying to get session directory from IncrCompSession `{:?}`",
                        *incr_comp_session)
                }
                IncrCompSession::Active { ref session_directory, .. } |
                IncrCompSession::Finalized { ref session_directory } |
                IncrCompSession::InvalidBecauseOfErrors { ref session_directory } => {
                    session_directory
                }
            }
        })
    }

    pub fn incr_comp_session_dir_opt(&self) -> Option<cell::Ref<PathBuf>> {
        if self.opts.incremental.is_some() {
            Some(self.incr_comp_session_dir())
        } else {
            None
        }
    }

    pub fn print_perf_stats(&self) {
        println!("Total time spent computing SVHs:               {}",
                 duration_to_secs_str(self.perf_stats.svh_time.get()));
        println!("Total time spent computing incr. comp. hashes: {}",
                 duration_to_secs_str(self.perf_stats.incr_comp_hashes_time.get()));
        println!("Total number of incr. comp. hashes computed:   {}",
                 self.perf_stats.incr_comp_hashes_count.get());
        println!("Total number of bytes hashed for incr. comp.:  {}",
                 self.perf_stats.incr_comp_bytes_hashed.get());
        println!("Average bytes hashed per incr. comp. HIR node: {}",
                 self.perf_stats.incr_comp_bytes_hashed.get() /
                 self.perf_stats.incr_comp_hashes_count.get());
        println!("Total time spent computing symbol hashes:      {}",
                 duration_to_secs_str(self.perf_stats.symbol_hash_time.get()));
        println!("Total time spent decoding DefPath tables:      {}",
                 duration_to_secs_str(self.perf_stats.decode_def_path_tables_time.get()));
    }

    /// We want to know if we're allowed to do an optimization for crate foo from -z fuel=foo=n.
    /// This expends fuel if applicable, and records fuel if applicable.
    pub fn consider_optimizing<T: Fn() -> String>(&self, crate_name: &str, msg: T) -> bool {
        let mut ret = true;
        match self.optimization_fuel_crate {
            Some(ref c) if c == crate_name => {
                let fuel = self.optimization_fuel_limit.get();
                ret = fuel != 0;
                if fuel == 0 && !self.out_of_fuel.get() {
                    println!("optimization-fuel-exhausted: {}", msg());
                    self.out_of_fuel.set(true);
                } else if fuel > 0 {
                    self.optimization_fuel_limit.set(fuel-1);
                }
            }
            _ => {}
        }
        match self.print_fuel_crate {
            Some(ref c) if c == crate_name=> {
                self.print_fuel.set(self.print_fuel.get()+1);
            },
            _ => {}
        }
        ret
    }
}

pub fn build_session(sopts: config::Options,
                     dep_graph: &DepGraph,
                     local_crate_source_file: Option<PathBuf>,
                     registry: errors::registry::Registry,
                     cstore: Rc<CrateStore>)
                     -> Session {
    let file_path_mapping = sopts.file_path_mapping();

    build_session_with_codemap(sopts,
                               dep_graph,
                               local_crate_source_file,
                               registry,
                               cstore,
                               Rc::new(codemap::CodeMap::new(file_path_mapping)),
                               None)
}

pub fn build_session_with_codemap(sopts: config::Options,
                                  dep_graph: &DepGraph,
                                  local_crate_source_file: Option<PathBuf>,
                                  registry: errors::registry::Registry,
                                  cstore: Rc<CrateStore>,
                                  codemap: Rc<codemap::CodeMap>,
                                  emitter_dest: Option<Box<Write + Send>>)
                                  -> Session {
    // FIXME: This is not general enough to make the warning lint completely override
    // normal diagnostic warnings, since the warning lint can also be denied and changed
    // later via the source code.
    let can_print_warnings = sopts.lint_opts
        .iter()
        .filter(|&&(ref key, _)| *key == "warnings")
        .map(|&(_, ref level)| *level != lint::Allow)
        .last()
        .unwrap_or(true);
    let treat_err_as_bug = sopts.debugging_opts.treat_err_as_bug;

    let emitter: Box<Emitter> = match (sopts.error_format, emitter_dest) {
        (config::ErrorOutputType::HumanReadable(color_config), None) => {
            Box::new(EmitterWriter::stderr(color_config,
                                           Some(codemap.clone())))
        }
        (config::ErrorOutputType::HumanReadable(_), Some(dst)) => {
            Box::new(EmitterWriter::new(dst,
                                        Some(codemap.clone())))
        }
        (config::ErrorOutputType::Json, None) => {
            Box::new(JsonEmitter::stderr(Some(registry), codemap.clone()))
        }
        (config::ErrorOutputType::Json, Some(dst)) => {
            Box::new(JsonEmitter::new(dst, Some(registry), codemap.clone()))
        }
    };

    let diagnostic_handler =
        errors::Handler::with_emitter(can_print_warnings,
                                      treat_err_as_bug,
                                      emitter);

    build_session_(sopts,
                   dep_graph,
                   local_crate_source_file,
                   diagnostic_handler,
                   codemap,
                   cstore)
}

pub fn build_session_(sopts: config::Options,
                      dep_graph: &DepGraph,
                      local_crate_source_file: Option<PathBuf>,
                      span_diagnostic: errors::Handler,
                      codemap: Rc<codemap::CodeMap>,
                      cstore: Rc<CrateStore>)
                      -> Session {
    let host = match Target::search(config::host_triple()) {
        Ok(t) => t,
        Err(e) => {
            panic!(span_diagnostic.fatal(&format!("Error loading host specification: {}", e)));
        }
    };
    let target_cfg = config::build_target_config(&sopts, &span_diagnostic);

    let p_s = parse::ParseSess::with_span_handler(span_diagnostic, codemap);
    let default_sysroot = match sopts.maybe_sysroot {
        Some(_) => None,
        None => Some(filesearch::get_or_default_sysroot())
    };

    let file_path_mapping = sopts.file_path_mapping();

    // Make the path absolute, if necessary
    let local_crate_source_file = local_crate_source_file.map(|path| {
        file_path_mapping.map_prefix(path.to_string_lossy().into_owned()).0
    });

    let optimization_fuel_crate = sopts.debugging_opts.fuel.as_ref().map(|i| i.0.clone());
    let optimization_fuel_limit = Cell::new(sopts.debugging_opts.fuel.as_ref()
        .map(|i| i.1).unwrap_or(0));
    let print_fuel_crate = sopts.debugging_opts.print_fuel.clone();
    let print_fuel = Cell::new(0);

    let working_dir = env::current_dir().unwrap().to_string_lossy().into_owned();
    let working_dir = file_path_mapping.map_prefix(working_dir);

    let sess = Session {
        dep_graph: dep_graph.clone(),
        target: target_cfg,
        host: host,
        opts: sopts,
        cstore: cstore,
        parse_sess: p_s,
        // For a library crate, this is always none
        entry_fn: RefCell::new(None),
        entry_type: Cell::new(None),
        plugin_registrar_fn: Cell::new(None),
        derive_registrar_fn: Cell::new(None),
        default_sysroot: default_sysroot,
        local_crate_source_file: local_crate_source_file,
        working_dir: working_dir,
        lint_store: RefCell::new(lint::LintStore::new()),
        lints: RefCell::new(lint::LintTable::new()),
        one_time_diagnostics: RefCell::new(FxHashSet()),
        plugin_llvm_passes: RefCell::new(Vec::new()),
        plugin_attributes: RefCell::new(Vec::new()),
        crate_types: RefCell::new(Vec::new()),
        dependency_formats: RefCell::new(FxHashMap()),
        crate_disambiguator: RefCell::new(Symbol::intern("")),
        features: RefCell::new(feature_gate::Features::new()),
        recursion_limit: Cell::new(64),
        type_length_limit: Cell::new(1048576),
        next_node_id: Cell::new(NodeId::new(1)),
        injected_allocator: Cell::new(None),
        allocator_kind: Cell::new(None),
        injected_panic_runtime: Cell::new(None),
        imported_macro_spans: RefCell::new(HashMap::new()),
        incr_comp_session: RefCell::new(IncrCompSession::NotInitialized),
        perf_stats: PerfStats {
            svh_time: Cell::new(Duration::from_secs(0)),
            incr_comp_hashes_time: Cell::new(Duration::from_secs(0)),
            incr_comp_hashes_count: Cell::new(0),
            incr_comp_bytes_hashed: Cell::new(0),
            symbol_hash_time: Cell::new(Duration::from_secs(0)),
            decode_def_path_tables_time: Cell::new(Duration::from_secs(0)),
        },
        code_stats: RefCell::new(CodeStats::new()),
        optimization_fuel_crate: optimization_fuel_crate,
        optimization_fuel_limit: optimization_fuel_limit,
        print_fuel_crate: print_fuel_crate,
        print_fuel: print_fuel,
        out_of_fuel: Cell::new(false),
        // Note that this is unsafe because it may misinterpret file descriptors
        // on Unix as jobserver file descriptors. We hopefully execute this near
        // the beginning of the process though to ensure we don't get false
        // positives, or in other words we try to execute this before we open
        // any file descriptors ourselves.
        //
        // Also note that we stick this in a global because there could be
        // multiple `Session` instances in this process, and the jobserver is
        // per-process.
        jobserver_from_env: unsafe {
            static mut GLOBAL_JOBSERVER: *mut Option<Client> = 0 as *mut _;
            static INIT: Once = ONCE_INIT;
            INIT.call_once(|| {
                GLOBAL_JOBSERVER = Box::into_raw(Box::new(Client::from_env()));
            });
            (*GLOBAL_JOBSERVER).clone()
        },
        has_global_allocator: Cell::new(false),
    };

    sess
}

/// Holds data on the current incremental compilation session, if there is one.
#[derive(Debug)]
pub enum IncrCompSession {
    // This is the state the session will be in until the incr. comp. dir is
    // needed.
    NotInitialized,
    // This is the state during which the session directory is private and can
    // be modified.
    Active {
        session_directory: PathBuf,
        lock_file: flock::Lock,
    },
    // This is the state after the session directory has been finalized. In this
    // state, the contents of the directory must not be modified any more.
    Finalized {
        session_directory: PathBuf,
    },
    // This is an error state that is reached when some compilation error has
    // occurred. It indicates that the contents of the session directory must
    // not be used, since they might be invalid.
    InvalidBecauseOfErrors {
        session_directory: PathBuf,
    }
}

pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
    let emitter: Box<Emitter> = match output {
        config::ErrorOutputType::HumanReadable(color_config) => {
            Box::new(EmitterWriter::stderr(color_config,
                                           None))
        }
        config::ErrorOutputType::Json => Box::new(JsonEmitter::basic()),
    };
    let handler = errors::Handler::with_emitter(true, false, emitter);
    handler.emit(&MultiSpan::new(), msg, errors::Level::Fatal);
    panic!(errors::FatalError);
}

pub fn early_warn(output: config::ErrorOutputType, msg: &str) {
    let emitter: Box<Emitter> = match output {
        config::ErrorOutputType::HumanReadable(color_config) => {
            Box::new(EmitterWriter::stderr(color_config,
                                           None))
        }
        config::ErrorOutputType::Json => Box::new(JsonEmitter::basic()),
    };
    let handler = errors::Handler::with_emitter(true, false, emitter);
    handler.emit(&MultiSpan::new(), msg, errors::Level::Warning);
}

#[derive(Copy, Clone, Debug)]
pub enum CompileIncomplete {
    Stopped,
    Errored(ErrorReported)
}
impl From<ErrorReported> for CompileIncomplete {
    fn from(err: ErrorReported) -> CompileIncomplete {
        CompileIncomplete::Errored(err)
    }
}
pub type CompileResult = Result<(), CompileIncomplete>;

pub fn compile_result_from_err_count(err_count: usize) -> CompileResult {
    if err_count == 0 {
        Ok(())
    } else {
        Err(CompileIncomplete::Errored(ErrorReported))
    }
}

#[cold]
#[inline(never)]
pub fn bug_fmt(file: &'static str, line: u32, args: fmt::Arguments) -> ! {
    // this wrapper mostly exists so I don't have to write a fully
    // qualified path of None::<Span> inside the bug!() macro defintion
    opt_span_bug_fmt(file, line, None::<Span>, args);
}

#[cold]
#[inline(never)]
pub fn span_bug_fmt<S: Into<MultiSpan>>(file: &'static str,
                                        line: u32,
                                        span: S,
                                        args: fmt::Arguments) -> ! {
    opt_span_bug_fmt(file, line, Some(span), args);
}

fn opt_span_bug_fmt<S: Into<MultiSpan>>(file: &'static str,
                                        line: u32,
                                        span: Option<S>,
                                        args: fmt::Arguments) -> ! {
    tls::with_opt(move |tcx| {
        let msg = format!("{}:{}: {}", file, line, args);
        match (tcx, span) {
            (Some(tcx), Some(span)) => tcx.sess.diagnostic().span_bug(span, &msg),
            (Some(tcx), None) => tcx.sess.diagnostic().bug(&msg),
            (None, _) => panic!(msg)
        }
    });
    unreachable!();
}