Rollup merge of rust-lang#64678 - tomtau:fix/no-std-error, r=matthewj…

…asper

added more context for duplicate lang item errors (fixes rust-lang#60561)

Some more information about rust-lang#60561 -- these errors are pretty common when one works in restrictive environments with `no_std` or customized `std`, but they don't provide much context for debugging, as any transitive dependency could have brought in `std` crate. With that, currently, one needs to use something like `cargo tree` and investigate transitive dependencies one by one.

It'll be more helpful to know at least the crate that uses `std` (which `cargo tree` doesn't show) to pin down this investigation when debugging.

I'm not sure what the best way to get this context is inside rustc internals (I'm new to them). I found that `all_crate_nums` query returns the crates in some dependency order, so printing out the name of the preceding crate seems to do the trick. But I welcome suggestions if this can be done in a better way.

src/librustc/middle/cstore.rs

@@ -126,10 +126,17 @@ pub struct ExternCrate {
  /// used to select the extern with the shortest path
  pub path_len: usize,
 
+ /// Crate that depends on this crate
+ pub dependency_of: CrateNum,
+}
+
+impl ExternCrate {
  /// If true, then this crate is the crate named by the extern
  /// crate referenced above. If false, then this crate is a dep
  /// of the crate.
- pub direct: bool,
+ pub fn is_direct(&self) -> bool {
+ self.dependency_of == LOCAL_CRATE
+ }
 }
 
 #[derive(Copy, Clone, Debug, HashStable)]

src/librustc/middle/lang_items.rs

@@ -13,6 +13,7 @@ use crate::hir::def_id::DefId;
 use crate::hir::check_attr::Target;
 use crate::ty::{self, TyCtxt};
 use crate::middle::weak_lang_items;
+use crate::middle::cstore::ExternCrate;
 use crate::util::nodemap::FxHashMap;
 
 use syntax::ast;
@@ -182,16 +183,39 @@ impl LanguageItemCollector<'tcx> {
  E0152,
  "duplicate lang item found: `{}`.",
  name),
- None => self.tcx.sess.struct_err(&format!(
- "duplicate lang item in crate `{}`: `{}`.",
- self.tcx.crate_name(item_def_id.krate),
- name)),
+ None => {
+ match self.tcx.extern_crate(item_def_id) {
+ Some(ExternCrate {dependency_of, ..}) => {
+ self.tcx.sess.struct_err(&format!(
+ "duplicate lang item in crate `{}` (which `{}` depends on): `{}`.",
+ self.tcx.crate_name(item_def_id.krate),
+ self.tcx.crate_name(*dependency_of),
+ name))
+ },
+ _ => {
+ self.tcx.sess.struct_err(&format!(
+ "duplicate lang item in crate `{}`: `{}`.",
+ self.tcx.crate_name(item_def_id.krate),
+ name))
+ }
+ }
+ },
  };
  if let Some(span) = self.tcx.hir().span_if_local(original_def_id) {
  span_note!(&mut err, span, "first defined here.");
  } else {
- err.note(&format!("first defined in crate `{}`.",
+ match self.tcx.extern_crate(original_def_id) {
+ Some(ExternCrate {dependency_of, ..}) => {
+ err.note(&format!(
+ "first defined in crate `{}` (which `{}` depends on).",
+ self.tcx.crate_name(original_def_id.krate),
+ self.tcx.crate_name(*dependency_of)));
+ },
+ _ => {
+ err.note(&format!("first defined in crate `{}`.",
  self.tcx.crate_name(original_def_id.krate)));
+ }
+ }
  }
  err.emit();
  }

src/librustc/ty/print/pretty.rs

@@ -278,7 +278,7 @@ pub trait PrettyPrinter<'tcx>:
  match self.tcx().extern_crate(def_id) {
  Some(&ExternCrate {
  src: ExternCrateSource::Extern(def_id),
- direct: true,
+ dependency_of: LOCAL_CRATE,
  span,
  ..
  }) => {

src/librustc_metadata/creader.rs

@@ -17,6 +17,7 @@ use rustc::middle::cstore::{ExternCrate, ExternCrateSource};
 use rustc::util::common::record_time;
 use rustc::util::nodemap::FxHashSet;
 use rustc::hir::map::Definitions;
+use rustc::hir::def_id::LOCAL_CRATE;
 
 use std::ops::Deref;
 use std::path::PathBuf;
@@ -430,7 +431,7 @@ impl<'a> CrateLoader<'a> {
  mut extern_crate: ExternCrate,
  visited: &mut FxHashSet<(CrateNum, bool)>)
  {
- if !visited.insert((cnum, extern_crate.direct)) { return }
+ if !visited.insert((cnum, extern_crate.is_direct())) { return }
 
  let cmeta = self.cstore.get_crate_data(cnum);
  let mut old_extern_crate = cmeta.extern_crate.borrow_mut();
@@ -441,14 +442,14 @@ impl<'a> CrateLoader<'a> {
  // - shorter paths to longer (tuple.2).
  let new_rank = (
  true,
- extern_crate.direct,
+ extern_crate.is_direct(),
  cmp::Reverse(extern_crate.path_len),
  );
  let old_rank = match *old_extern_crate {
  None => (false, false, cmp::Reverse(usize::max_value())),
  Some(ref c) => (
  true,
- c.direct,
+ c.is_direct(),
  cmp::Reverse(c.path_len),
  ),
  };
@@ -460,7 +461,7 @@ impl<'a> CrateLoader<'a> {
  drop(old_extern_crate);
 
  // Propagate the extern crate info to dependencies.
- extern_crate.direct = false;
+ extern_crate.dependency_of = cnum;
  for &dep_cnum in cmeta.dependencies.borrow().iter() {
  self.update_extern_crate(dep_cnum, extern_crate, visited);
  }
@@ -1030,7 +1031,7 @@ impl<'a> CrateLoader<'a> {
  src: ExternCrateSource::Extern(def_id),
  span: item.span,
  path_len,
- direct: true,
+ dependency_of: LOCAL_CRATE,
  },
  &mut FxHashSet::default(),
  );
@@ -1057,7 +1058,7 @@ impl<'a> CrateLoader<'a> {
  span,
  // to have the least priority in `update_extern_crate`
  path_len: usize::max_value(),
- direct: true,
+ dependency_of: LOCAL_CRATE,
  },
  &mut FxHashSet::default(),
  );
@@ -1081,7 +1082,7 @@ impl<'a> CrateLoader<'a> {
  span,
  // to have the least priority in `update_extern_crate`
  path_len: usize::max_value(),
- direct: true,
+ dependency_of: LOCAL_CRATE,
  },
  &mut FxHashSet::default(),
  );

src/librustc_metadata/cstore_impl.rs

@@ -233,7 +233,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
 
  missing_extern_crate_item => {
  let r = match *cdata.extern_crate.borrow() {
- Some(extern_crate) if !extern_crate.direct => true,
+ Some(extern_crate) if !extern_crate.is_direct() => true,
  _ => false,
  };
  r

src/test/ui/duplicate_entry_error.stderr

@@ -7,7 +7,7 @@ LL | | loop {}
 LL | | }
  | |_^
  |
- = note: first defined in crate `std`.
+ = note: first defined in crate `std` (which `duplicate_entry_error` depends on).
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0152.stderr

@@ -4,7 +4,7 @@ error[E0152]: duplicate lang item found: `arc`.
 LL | struct Foo;
  | ^^^^^^^^^^^
  |
- = note: first defined in crate `alloc`.
+ = note: first defined in crate `alloc` (which `std` depends on).
 
 error: aborting due to previous error
 

src/test/ui/panic-handler/panic-handler-std.stderr

@@ -6,7 +6,7 @@ LL | | loop {}
 LL | | }
  | |_^
  |
- = note: first defined in crate `std`.
+ = note: first defined in crate `std` (which `panic_handler_std` depends on).
 
 error: argument should be `&PanicInfo`
  --> $DIR/panic-handler-std.rs:7:16