pretty: trim paths of unique symbols

If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.

This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.

This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.

On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.

This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.

Author: da-x

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -4,6 +4,7 @@ use crate::type_::Type;
 use rustc_codegen_ssa::traits::*;
 use rustc_middle::bug;
 use rustc_middle::ty::layout::{FnAbiExt, TyAndLayout};
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Ty, TypeFoldable};
 use rustc_target::abi::{Abi, AddressSpace, Align, FieldsShape};
 use rustc_target::abi::{Int, Pointer, F32, F64};
@@ -57,7 +58,7 @@ fn uncached_llvm_type<'a, 'tcx>(
         ty::Adt(..) | ty::Closure(..) | ty::Foreign(..) | ty::Generator(..) | ty::Str
             if !cx.sess().fewer_names() =>
         {
-            let mut name = layout.ty.to_string();
+            let mut name = with_no_trimmed_paths(|| layout.ty.to_string());
             if let (&ty::Adt(def, _), &Variants::Single { index }) =
                 (&layout.ty.kind, &layout.variants)
             {

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -16,6 +16,7 @@ use rustc_middle::mir;
 use rustc_middle::mir::interpret::{AllocId, ConstValue, Pointer, Scalar};
 use rustc_middle::mir::AssertKind;
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
@@ -479,14 +480,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 UninitValid => !layout.might_permit_raw_init(bx, /*zero:*/ false).unwrap(),
             };
             if do_panic {
-                let msg_str = if layout.abi.is_uninhabited() {
-                    // Use this error even for the other intrinsics as it is more precise.
-                    format!("attempted to instantiate uninhabited type `{}`", ty)
-                } else if intrinsic == ZeroValid {
-                    format!("attempted to zero-initialize type `{}`, which is invalid", ty)
-                } else {
-                    format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
-                };
+                let msg_str = with_no_trimmed_paths(|| {
+                    if layout.abi.is_uninhabited() {
+                        // Use this error even for the other intrinsics as it is more precise.
+                        format!("attempted to instantiate uninhabited type `{}`", ty)
+                    } else if intrinsic == ZeroValid {
+                        format!("attempted to zero-initialize type `{}`, which is invalid", ty)
+                    } else {
+                        format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
+                    }
+                });
                 let msg = bx.const_str(Symbol::intern(&msg_str));
                 let location = self.get_caller_location(bx, span).immediate();
 

compiler/rustc_driver/src/lib.rs

@@ -34,7 +34,7 @@ use rustc_save_analysis as save;
 use rustc_save_analysis::DumpHandler;
 use rustc_serialize::json::{self, ToJson};
 use rustc_session::config::nightly_options;
-use rustc_session::config::{ErrorOutputType, Input, OutputType, PrintRequest};
+use rustc_session::config::{ErrorOutputType, Input, OutputType, PrintRequest, TrimmedDefPaths};
 use rustc_session::getopts;
 use rustc_session::lint::{Lint, LintId};
 use rustc_session::{config, DiagnosticOutput, Session};
@@ -159,7 +159,10 @@ pub fn run_compiler(
         None => return Ok(()),
     };
 
-    let sopts = config::build_session_options(&matches);
+    let sopts = config::Options {
+        trimmed_def_paths: TrimmedDefPaths::GoodPath,
+        ..config::build_session_options(&matches)
+    };
     let cfg = interface::parse_cfgspecs(matches.opt_strs("cfg"));
 
     let mut dummy_config = |sopts, cfg, diagnostic_output| {

compiler/rustc_interface/src/tests.rs

@@ -518,6 +518,7 @@ fn test_debugging_options_tracking_hash() {
     untracked!(time_llvm_passes, true);
     untracked!(time_passes, true);
     untracked!(trace_macros, true);
+    untracked!(trim_diagnostic_paths, false);
     untracked!(ui_testing, true);
     untracked!(unpretty, Some("expanded".to_string()));
     untracked!(unstable_options, true);

compiler/rustc_lint/src/context.rs

@@ -31,6 +31,7 @@ use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::middle::privacy::AccessLevels;
 use rustc_middle::middle::stability;
 use rustc_middle::ty::layout::{LayoutError, TyAndLayout};
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
 use rustc_session::lint::{add_elided_lifetime_in_path_suggestion, BuiltinLintDiagnostics};
 use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
@@ -795,10 +796,12 @@ impl<'tcx> LateContext<'tcx> {
                 }
 
                 // This shouldn't ever be needed, but just in case:
-                Ok(vec![match trait_ref {
-                    Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
-                    None => Symbol::intern(&format!("<{}>", self_ty)),
-                }])
+                with_no_trimmed_paths(|| {
+                    Ok(vec![match trait_ref {
+                        Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
+                        None => Symbol::intern(&format!("<{}>", self_ty)),
+                    }])
+                })
             }
 
             fn path_append_impl(
@@ -812,12 +815,16 @@ impl<'tcx> LateContext<'tcx> {
 
                 // This shouldn't ever be needed, but just in case:
                 path.push(match trait_ref {
-                    Some(trait_ref) => Symbol::intern(&format!(
-                        "<impl {} for {}>",
-                        trait_ref.print_only_trait_path(),
-                        self_ty
-                    )),
-                    None => Symbol::intern(&format!("<impl {}>", self_ty)),
+                    Some(trait_ref) => with_no_trimmed_paths(|| {
+                        Symbol::intern(&format!(
+                            "<impl {} for {}>",
+                            trait_ref.print_only_trait_path(),
+                            self_ty
+                        ))
+                    }),
+                    None => {
+                        with_no_trimmed_paths(|| Symbol::intern(&format!("<impl {}>", self_ty)))
+                    }
                 });
 
                 Ok(path)

compiler/rustc_macros/src/query.rs

@@ -392,7 +392,7 @@ fn add_query_description_impl(
             #tcx: TyCtxt<'tcx>,
             #key: #arg,
         ) -> Cow<'static, str> {
-            format!(#desc).into()
+            ::rustc_middle::ty::print::with_no_trimmed_paths(|| format!(#desc).into())
         }
     };
 

compiler/rustc_middle/src/middle/stability.rs

@@ -13,6 +13,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX};
 use rustc_hir::{self, HirId};
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::lint::builtin::{DEPRECATED, DEPRECATED_IN_FUTURE, SOFT_UNSTABLE};
 use rustc_session::lint::{BuiltinLintDiagnostics, Lint, LintBuffer};
 use rustc_session::parse::feature_err_issue;
@@ -308,7 +309,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 // #[rustc_deprecated] however wants to emit down the whole
                 // hierarchy.
                 if !skip || depr_entry.attr.is_since_rustc_version {
-                    let path = &self.def_path_str(def_id);
+                    let path = &with_no_trimmed_paths(|| self.def_path_str(def_id));
                     let kind = self.def_kind(def_id).descr(def_id);
                     let (message, lint) = deprecation_message(&depr_entry.attr, kind, path);
                     late_report_deprecation(

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -108,6 +108,7 @@ use rustc_data_structures::sync::{HashMapExt, Lock};
 use rustc_data_structures::tiny_list::TinyList;
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_serialize::{Decodable, Encodable};
 use rustc_target::abi::{Endian, Size};
 
@@ -145,7 +146,7 @@ pub struct GlobalId<'tcx> {
 
 impl GlobalId<'tcx> {
     pub fn display(self, tcx: TyCtxt<'tcx>) -> String {
-        let instance_name = tcx.def_path_str(self.instance.def.def_id());
+        let instance_name = with_no_trimmed_paths(|| tcx.def_path_str(self.instance.def.def_id()));
         if let Some(promoted) = self.promoted {
             format!("{}::{:?}", instance_name, promoted)
         } else {

compiler/rustc_middle/src/query/mod.rs

@@ -1255,6 +1255,11 @@ rustc_queries! {
             storage(ArenaCacheSelector<'tcx>)
             desc { "calculating the visible parent map" }
         }
+        query trimmed_def_paths(_: CrateNum)
+            -> FxHashMap<DefId, Symbol> {
+            storage(ArenaCacheSelector<'tcx>)
+            desc { "calculating trimmed def paths" }
+        }
         query missing_extern_crate_item(_: CrateNum) -> bool {
             eval_always
             desc { "seeing if we're missing an `extern crate` item for this crate" }

compiler/rustc_middle/src/ty/context.rs

@@ -943,7 +943,7 @@ pub struct GlobalCtxt<'tcx> {
     maybe_unused_extern_crates: Vec<(LocalDefId, Span)>,
     /// A map of glob use to a set of names it actually imports. Currently only
     /// used in save-analysis.
-    glob_map: FxHashMap<LocalDefId, FxHashSet<Symbol>>,
+    pub(crate) glob_map: FxHashMap<LocalDefId, FxHashSet<Symbol>>,
     /// Extern prelude entries. The value is `true` if the entry was introduced
     /// via `extern crate` item and not `--extern` option or compiler built-in.
     pub extern_prelude: FxHashMap<Symbol, bool>,

compiler/rustc_middle/src/ty/mod.rs

@@ -3101,6 +3101,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
     erase_regions::provide(providers);
     layout::provide(providers);
     util::provide(providers);
+    print::provide(providers);
     super::util::bug::provide(providers);
     *providers = ty::query::Providers {
         trait_impls_of: trait_def::trait_impls_of_provider,