Internal lints: usage_of_qualified_ty & ty_pass_by_reference

src/librustc/infer/error_reporting/mod.rs

@@ -690,7 +690,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         name: String,
         sub: ty::subst::SubstsRef<'tcx>,
         pos: usize,
-        other_ty: &Ty<'tcx>,
+        other_ty: Ty<'tcx>,
     ) {
         // `value` and `other_value` hold two incomplete type representation for display.
         // `name` is the path of both types being compared. `sub`
@@ -768,10 +768,10 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         path: String,
         sub: ty::subst::SubstsRef<'tcx>,
         other_path: String,
-        other_ty: &Ty<'tcx>,
+        other_ty: Ty<'tcx>,
     ) -> Option<()> {
         for (i, ta) in sub.types().enumerate() {
-            if &ta == other_ty {
+            if ta == other_ty {
                 self.highlight_outer(&mut t1_out, &mut t2_out, path, sub, i, &other_ty);
                 return Some(());
             }
@@ -839,7 +839,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     /// Compares two given types, eliding parts that are the same between them and highlighting
     /// relevant differences, and return two representation of those types for highlighted printing.
     fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
-        fn equals<'tcx>(a: &Ty<'tcx>, b: &Ty<'tcx>) -> bool {
+        fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
             match (&a.sty, &b.sty) {
                 (a, b) if *a == *b => true,
                 (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
@@ -1099,7 +1099,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         };
 
-        let span = cause.span(&self.tcx);
+        let span = cause.span(self.tcx);
 
         diag.span_label(span, terr.to_string());
         if let Some((sp, msg)) = secondary_span {
@@ -1233,7 +1233,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             trace, terr
         );
 
-        let span = trace.cause.span(&self.tcx);
+        let span = trace.cause.span(self.tcx);
         let failure_code = trace.cause.as_failure_code(terr);
         let mut diag = match failure_code {
             FailureCode::Error0317(failure_str) => {

src/librustc/infer/error_reporting/need_type_info.rs

@@ -11,7 +11,7 @@ use errors::DiagnosticBuilder;
 
 struct FindLocalByTypeVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
-    target_ty: &'a Ty<'tcx>,
+    target_ty: Ty<'tcx>,
     hir_map: &'a hir::map::Map<'gcx>,
     found_local_pattern: Option<&'gcx Pat>,
     found_arg_pattern: Option<&'gcx Pat>,
@@ -26,7 +26,7 @@ impl<'a, 'gcx, 'tcx> FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
             Some(ty) => {
                 let ty = self.infcx.resolve_type_vars_if_possible(&ty);
                 ty.walk().any(|inner_ty| {
-                    inner_ty == *self.target_ty || match (&inner_ty.sty, &self.target_ty.sty) {
+                    inner_ty == self.target_ty || match (&inner_ty.sty, &self.target_ty.sty) {
                         (&Infer(TyVar(a_vid)), &Infer(TyVar(b_vid))) => {
                             self.infcx
                                 .type_variables
@@ -68,10 +68,10 @@ impl<'a, 'gcx, 'tcx> Visitor<'gcx> for FindLocalByTypeVisitor<'a, 'gcx, 'tcx> {
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn extract_type_name(
         &self,
-        ty: &'a Ty<'tcx>,
+        ty: Ty<'tcx>,
         highlight: Option<ty::print::RegionHighlightMode>,
     ) -> String {
-        if let ty::Infer(ty::TyVar(ty_vid)) = (*ty).sty {
+        if let ty::Infer(ty::TyVar(ty_vid)) = ty.sty {
             let ty_vars = self.type_variables.borrow();
             if let TypeVariableOrigin::TypeParameterDefinition(_, name) =
                 *ty_vars.var_origin(ty_vid) {
@@ -102,7 +102,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         let mut local_visitor = FindLocalByTypeVisitor {
             infcx: &self,
-            target_ty: &ty,
+            target_ty: ty,
             hir_map: &self.tcx.hir(),
             found_local_pattern: None,
             found_arg_pattern: None,

src/librustc/infer/error_reporting/nice_region_error/placeholder_error.rs

@@ -193,7 +193,7 @@ impl NiceRegionError<'me, 'gcx, 'tcx> {
         );
 
         let mut err = self.tcx().sess.struct_span_err(
-            cause.span(&self.tcx()),
+            cause.span(self.tcx()),
             &format!(
                 "implementation of `{}` is not general enough",
                 self.tcx().def_path_str(trait_def_id),

src/librustc/infer/nll_relate/mod.rs

@@ -267,7 +267,7 @@ where
     fn relate_projection_ty(
         &mut self,
         projection_ty: ty::ProjectionTy<'tcx>,
-        value_ty: ty::Ty<'tcx>,
+        value_ty: Ty<'tcx>,
     ) -> Ty<'tcx> {
         use crate::infer::type_variable::TypeVariableOrigin;
         use crate::traits::WhereClause;

src/librustc/lint/internal.rs

@@ -1,7 +1,7 @@
 //! Some lints that are only useful in the compiler or crates that use compiler internals, such as
 //! Clippy.
 
-use crate::hir::{HirId, Path, PathSegment, QPath, Ty, TyKind};
+use crate::hir::{GenericArg, HirId, MutTy, Mutability, Path, PathSegment, QPath, Ty, TyKind};
 use crate::lint::{
     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintArray, LintContext, LintPass,
 };
@@ -57,12 +57,28 @@ impl EarlyLintPass for DefaultHashTypes {
 declare_lint! {
     pub USAGE_OF_TY_TYKIND,
     Allow,
-    "Usage of `ty::TyKind` outside of the `ty::sty` module"
+    "usage of `ty::TyKind` outside of the `ty::sty` module"
 }
 
-declare_lint_pass!(TyKindUsage => [USAGE_OF_TY_TYKIND]);
+declare_lint! {
+    pub TY_PASS_BY_REFERENCE,
+    Allow,
+    "passing `Ty` or `TyCtxt` by reference"
+}
+
+declare_lint! {
+    pub USAGE_OF_QUALIFIED_TY,
+    Allow,
+    "using `ty::{Ty,TyCtxt}` instead of importing it"
+}
+
+declare_lint_pass!(TyTyKind => [
+    USAGE_OF_TY_TYKIND,
+    TY_PASS_BY_REFERENCE,
+    USAGE_OF_QUALIFIED_TY,
+]);
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TyKindUsage {
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TyTyKind {
     fn check_path(&mut self, cx: &LateContext<'_, '_>, path: &'tcx Path, _: HirId) {
         let segments = path.segments.iter().rev().skip(1).rev();
 
@@ -82,16 +98,72 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TyKindUsage {
     }
 
     fn check_ty(&mut self, cx: &LateContext<'_, '_>, ty: &'tcx Ty) {
-        if let TyKind::Path(qpath) = &ty.node {
-            if let QPath::Resolved(_, path) = qpath {
-                if let Some(last) = path.segments.iter().last() {
-                    if lint_ty_kind_usage(cx, last) {
-                        cx.struct_span_lint(USAGE_OF_TY_TYKIND, path.span, "usage of `ty::TyKind`")
-                            .help("try using `ty::Ty` instead")
+        match &ty.node {
+            TyKind::Path(qpath) => {
+                if let QPath::Resolved(_, path) = qpath {
+                    if let Some(last) = path.segments.iter().last() {
+                        if lint_ty_kind_usage(cx, last) {
+                            cx.struct_span_lint(
+                                USAGE_OF_TY_TYKIND,
+                                path.span,
+                                "usage of `ty::TyKind`",
+                            )
+                            .help("try using `Ty` instead")
                             .emit();
+                        } else {
+                            if ty.span.ctxt().outer().expn_info().is_some() {
+                                return;
+                            }
+                            if let Some(t) = is_ty_or_ty_ctxt(cx, ty) {
+                                if path.segments.len() > 1 {
+                                    cx.struct_span_lint(
+                                        USAGE_OF_QUALIFIED_TY,
+                                        path.span,
+                                        &format!("usage of qualified `ty::{}`", t),
+                                    )
+                                    .span_suggestion(
+                                        path.span,
+                                        "try using it unqualified",
+                                        t,
+                                        // The import probably needs to be changed
+                                        Applicability::MaybeIncorrect,
+                                    )
+                                    .emit();
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            TyKind::Rptr(
+                _,
+                MutTy {
+                    ty: inner_ty,
+                    mutbl: Mutability::MutImmutable,
+                },
+            ) => {
+                if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner_def_id()) {
+                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
+                        return;
                     }
                 }
+                if let Some(t) = is_ty_or_ty_ctxt(cx, &inner_ty) {
+                    cx.struct_span_lint(
+                        TY_PASS_BY_REFERENCE,
+                        ty.span,
+                        &format!("passing `{}` by reference", t),
+                    )
+                    .span_suggestion(
+                        ty.span,
+                        "try passing by value",
+                        t,
+                        // Changing type of function argument
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit();
+                }
             }
+            _ => {}
         }
     }
 }
@@ -107,3 +179,43 @@ fn lint_ty_kind_usage(cx: &LateContext<'_, '_>, segment: &PathSegment) -> bool {
 
     false
 }
+
+fn is_ty_or_ty_ctxt(cx: &LateContext<'_, '_>, ty: &Ty) -> Option<String> {
+    match &ty.node {
+        TyKind::Path(qpath) => {
+            if let QPath::Resolved(_, path) = qpath {
+                let did = path.def.opt_def_id()?;
+                if cx.match_def_path(did, &["rustc", "ty", "Ty"]) {
+                    return Some(format!("Ty{}", gen_args(path.segments.last().unwrap())));
+                } else if cx.match_def_path(did, &["rustc", "ty", "context", "TyCtxt"]) {
+                    return Some(format!("TyCtxt{}", gen_args(path.segments.last().unwrap())));
+                }
+            }
+        }
+        _ => {}
+    }
+
+    None
+}
+
+fn gen_args(segment: &PathSegment) -> String {
+    if let Some(args) = &segment.args {
+        let lifetimes = args
+            .args
+            .iter()
+            .filter_map(|arg| {
+                if let GenericArg::Lifetime(lt) = arg {
+                    Some(lt.name.ident().to_string())
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>();
+
+        if !lifetimes.is_empty() {
+            return format!("<{}>", lifetimes.join(", "));
+        }
+    }
+
+    String::new()
+}

src/librustc/middle/exported_symbols.rs

@@ -4,7 +4,7 @@ use rustc_data_structures::stable_hasher::{StableHasher, HashStable,
                                            StableHasherResult};
 use std::cmp;
 use std::mem;
-use crate::ty;
+use crate::ty::{self, TyCtxt};
 use crate::ty::subst::SubstsRef;
 
 /// The SymbolExportLevel of a symbols specifies from which kinds of crates
@@ -39,7 +39,7 @@ pub enum ExportedSymbol<'tcx> {
 
 impl<'tcx> ExportedSymbol<'tcx> {
     pub fn symbol_name(&self,
-                       tcx: ty::TyCtxt<'_, 'tcx, '_>)
+                       tcx: TyCtxt<'_, 'tcx, '_>)
                        -> ty::SymbolName {
         match *self {
             ExportedSymbol::NonGeneric(def_id) => {
@@ -55,7 +55,7 @@ impl<'tcx> ExportedSymbol<'tcx> {
     }
 
     pub fn compare_stable(&self,
-                          tcx: ty::TyCtxt<'_, 'tcx, '_>,
+                          tcx: TyCtxt<'_, 'tcx, '_>,
                           other: &ExportedSymbol<'tcx>)
                           -> cmp::Ordering {
         match *self {
@@ -92,7 +92,7 @@ impl<'tcx> ExportedSymbol<'tcx> {
     }
 }
 
-pub fn metadata_symbol_name(tcx: ty::TyCtxt<'_, '_, '_>) -> String {
+pub fn metadata_symbol_name(tcx: TyCtxt<'_, '_, '_>) -> String {
     format!("rust_metadata_{}_{}",
             tcx.original_crate_name(LOCAL_CRATE),
             tcx.crate_disambiguator(LOCAL_CRATE).to_fingerprint().to_hex())

src/librustc/mir/mono.rs

@@ -18,7 +18,7 @@ pub enum MonoItem<'tcx> {
 }
 
 impl<'tcx> MonoItem<'tcx> {
-    pub fn size_estimate<'a>(&self, tcx: &TyCtxt<'a, 'tcx, 'tcx>) -> usize {
+    pub fn size_estimate<'a>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> usize {
         match *self {
             MonoItem::Fn(instance) => {
                 // Estimate the size of a function based on how many statements
@@ -144,7 +144,7 @@ impl<'tcx> CodegenUnit<'tcx> {
         base_n::encode(hash, base_n::CASE_INSENSITIVE)
     }
 
-    pub fn estimate_size<'a>(&mut self, tcx: &TyCtxt<'a, 'tcx, 'tcx>) {
+    pub fn estimate_size<'a>(&mut self, tcx: TyCtxt<'a, 'tcx, 'tcx>) {
         // Estimate the size of a codegen unit as (approximately) the number of MIR
         // statements it corresponds to.
         self.size_estimate = Some(self.items.keys().map(|mi| mi.size_estimate(tcx)).sum());

src/librustc/mir/visit.rs

@@ -198,7 +198,7 @@ macro_rules! make_mir_visitor {
             }
 
             fn visit_ty(&mut self,
-                        ty: & $($mutability)? Ty<'tcx>,
+                        ty: $(& $mutability)? Ty<'tcx>,
                         _: TyContext) {
                 self.super_ty(ty);
             }
@@ -864,7 +864,7 @@ macro_rules! make_mir_visitor {
                 self.visit_ty(& $($mutability)? ty.inferred_ty, TyContext::UserTy(ty.span));
             }
 
-            fn super_ty(&mut self, _ty: & $($mutability)? Ty<'tcx>) {
+            fn super_ty(&mut self, _ty: $(& $mutability)? Ty<'tcx>) {
             }
 
             fn super_region(&mut self, _region: & $($mutability)? ty::Region<'tcx>) {

src/librustc/traits/auto_trait.rs

@@ -49,11 +49,11 @@ pub struct AutoTraitInfo<'cx> {
 }
 
 pub struct AutoTraitFinder<'a, 'tcx: 'a> {
-    tcx: &'a TyCtxt<'a, 'tcx, 'tcx>,
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
 }
 
 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
-    pub fn new(tcx: &'a TyCtxt<'a, 'tcx, 'tcx>) -> Self {
+    pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self {
         AutoTraitFinder { tcx }
     }
 
@@ -291,7 +291,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
         infcx: &InferCtxt<'b, 'tcx, 'c>,
         ty_did: DefId,
         trait_did: DefId,
-        ty: ty::Ty<'c>,
+        ty: Ty<'c>,
         param_env: ty::ParamEnv<'c>,
         user_env: ty::ParamEnv<'c>,
         fresh_preds: &mut FxHashSet<ty::Predicate<'c>>,
@@ -661,7 +661,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
         T: Iterator<Item = Obligation<'cx, ty::Predicate<'cx>>>,
     >(
         &self,
-        ty: ty::Ty<'_>,
+        ty: Ty<'_>,
         nested: T,
         computed_preds: &'b mut FxHashSet<ty::Predicate<'cx>>,
         fresh_preds: &'b mut FxHashSet<ty::Predicate<'cx>>,

src/librustc/traits/error_reporting.rs

@@ -1242,7 +1242,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                            found: ty::PolyTraitRef<'tcx>)
         -> DiagnosticBuilder<'tcx>
     {
-        fn build_fn_sig_string<'a, 'gcx, 'tcx>(tcx: ty::TyCtxt<'a, 'gcx, 'tcx>,
+        fn build_fn_sig_string<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
                                                trait_ref: &ty::TraitRef<'tcx>) -> String {
             let inputs = trait_ref.substs.type_at(1);
             let sig = if let ty::Tuple(inputs) = inputs.sty {

src/librustc/traits/mod.rs

@@ -138,7 +138,7 @@ pub struct ObligationCause<'tcx> {
 }
 
 impl<'tcx> ObligationCause<'tcx> {
-    pub fn span<'a, 'gcx>(&self, tcx: &TyCtxt<'a, 'gcx, 'tcx>) -> Span {
+    pub fn span<'a, 'gcx>(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Span {
         match self.code {
             ObligationCauseCode::CompareImplMethodObligation { .. } |
             ObligationCauseCode::MainFunctionType |