Desugar parenthesized generic arguments in HIR

Author: petrochenkov

src/librustc/diagnostics.rs

@@ -687,6 +687,21 @@ attributes:
 See also https://doc.rust-lang.org/book/first-edition/no-stdlib.html
 "##,
 
+E0214: r##"
+A generic type was described using parentheses rather than angle brackets. For
+example:
+
+```compile_fail,E0214
+fn main() {
+    let v: Vec(&str) = vec!["foo"];
+}
+```
+
+This is not currently supported: `v` should be defined as `Vec<&str>`.
+Parentheses are currently only used with generic types when defining parameters
+for `Fn`-family traits.
+"##,
+
 E0261: r##"
 When using a lifetime like `'a` in a type, it must be declared before being
 used.

src/librustc/hir/intravisit.rs

@@ -617,17 +617,9 @@ pub fn walk_path_segment<'v, V: Visitor<'v>>(visitor: &mut V,
 pub fn walk_path_parameters<'v, V: Visitor<'v>>(visitor: &mut V,
                                                 _path_span: Span,
                                                 path_parameters: &'v PathParameters) {
-    match *path_parameters {
-        AngleBracketedParameters(ref data) => {
-            walk_list!(visitor, visit_ty, &data.types);
-            walk_list!(visitor, visit_lifetime, &data.lifetimes);
-            walk_list!(visitor, visit_assoc_type_binding, &data.bindings);
-        }
-        ParenthesizedParameters(ref data) => {
-            walk_list!(visitor, visit_ty, &data.inputs);
-            walk_list!(visitor, visit_ty, &data.output);
-        }
-    }
+    walk_list!(visitor, visit_lifetime, &path_parameters.lifetimes);
+    walk_list!(visitor, visit_ty, &path_parameters.types);
+    walk_list!(visitor, visit_assoc_type_binding, &path_parameters.bindings);
 }
 
 pub fn walk_assoc_type_binding<'v, V: Visitor<'v>>(visitor: &mut V,

src/librustc/hir/lowering.rs

@@ -45,15 +45,16 @@ use hir::map::{Definitions, DefKey, REGULAR_SPACE};
 use hir::map::definitions::DefPathData;
 use hir::def_id::{DefIndex, DefId, CRATE_DEF_INDEX};
 use hir::def::{Def, PathResolution};
+use lint::builtin::PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES;
 use rustc_data_structures::indexed_vec::IndexVec;
 use session::Session;
+use util::common::FN_OUTPUT_NAME;
 use util::nodemap::{DefIdMap, FxHashMap, NodeMap};
 
 use std::collections::BTreeMap;
 use std::fmt::Debug;
 use std::iter;
 use std::mem;
-
 use syntax::attr;
 use syntax::ast::*;
 use syntax::errors;
@@ -160,6 +161,12 @@ struct LoweredNodeId {
     hir_id: hir::HirId,
 }
 
+enum ParenthesizedGenericArgs {
+    Ok,
+    Warn,
+    Err,
+}
+
 impl<'a> LoweringContext<'a> {
     fn lower_crate(mut self, c: &Crate) -> hir::Crate {
         /// Full-crate AST visitor that inserts into a fresh
@@ -749,6 +756,21 @@ impl<'a> LoweringContext<'a> {
                     Def::Trait(def_id) if i + 1 == proj_start => Some(def_id),
                     _ => None
                 };
+                let parenthesized_generic_args = match resolution.base_def() {
+                    // `a::b::Trait(Args)`
+                    Def::Trait(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Ok,
+                    // `a::b::Trait(Args)::TraitItem`
+                    Def::Method(..) |
+                    Def::AssociatedConst(..) |
+                    Def::AssociatedTy(..) if i + 2 == proj_start => ParenthesizedGenericArgs::Ok,
+                    // Avoid duplicated errors
+                    Def::Err => ParenthesizedGenericArgs::Ok,
+                    // An error
+                    Def::Struct(..) | Def::Enum(..) | Def::Union(..) | Def::TyAlias(..) |
+                    Def::Variant(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Err,
+                    // A warning for now, for compatibility reasons
+                    _ => ParenthesizedGenericArgs::Warn,
+                };
 
                 let num_lifetimes = type_def_id.map_or(0, |def_id| {
                     if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
@@ -759,7 +781,8 @@ impl<'a> LoweringContext<'a> {
                     self.type_def_lifetime_params.insert(def_id, n);
                     n
                 });
-                self.lower_path_segment(p.span, segment, param_mode, num_lifetimes)
+                self.lower_path_segment(p.span, segment, param_mode, num_lifetimes,
+                                        parenthesized_generic_args)
             }).collect(),
             span: p.span,
         });
@@ -794,7 +817,8 @@ impl<'a> LoweringContext<'a> {
         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
-            let segment = P(self.lower_path_segment(p.span, segment, param_mode, 0));
+            let segment = P(self.lower_path_segment(p.span, segment, param_mode, 0,
+                                                    ParenthesizedGenericArgs::Warn));
             let qpath = hir::QPath::TypeRelative(ty, segment);
 
             // It's finished, return the extension of the right node type.
@@ -827,7 +851,8 @@ impl<'a> LoweringContext<'a> {
         hir::Path {
             def: self.expect_full_def(id),
             segments: segments.map(|segment| {
-                self.lower_path_segment(p.span, segment, param_mode, 0)
+                self.lower_path_segment(p.span, segment, param_mode, 0,
+                                        ParenthesizedGenericArgs::Err)
             }).chain(name.map(|name| {
                 hir::PathSegment {
                     name,
@@ -851,29 +876,37 @@ impl<'a> LoweringContext<'a> {
                           path_span: Span,
                           segment: &PathSegment,
                           param_mode: ParamMode,
-                          expected_lifetimes: usize)
+                          expected_lifetimes: usize,
+                          parenthesized_generic_args: ParenthesizedGenericArgs)
                           -> hir::PathSegment {
         let mut parameters = if let Some(ref parameters) = segment.parameters {
+            let msg = "parenthesized parameters may only be used with a trait";
             match **parameters {
                 PathParameters::AngleBracketed(ref data) => {
-                    let data = self.lower_angle_bracketed_parameter_data(data, param_mode);
-                    hir::AngleBracketedParameters(data)
+                    self.lower_angle_bracketed_parameter_data(data, param_mode)
                 }
-                PathParameters::Parenthesized(ref data) => {
-                    hir::ParenthesizedParameters(self.lower_parenthesized_parameter_data(data))
+                PathParameters::Parenthesized(ref data) => match parenthesized_generic_args {
+                    ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
+                    ParenthesizedGenericArgs::Warn => {
+                        self.sess.buffer_lint(PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
+                                              CRATE_NODE_ID, data.span, msg.into());
+                        hir::PathParameters::none()
+                    }
+                    ParenthesizedGenericArgs::Err => {
+                        struct_span_err!(self.sess, data.span, E0214, "{}", msg)
+                            .span_label(data.span, "only traits may use parentheses").emit();
+                        hir::PathParameters::none()
+                    }
                 }
             }
         } else {
-            let data = self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode);
-            hir::AngleBracketedParameters(data)
+            self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode)
         };
 
-        if let hir::AngleBracketedParameters(ref mut data) = parameters {
-            if data.lifetimes.is_empty() {
-                data.lifetimes = (0..expected_lifetimes).map(|_| {
-                    self.elided_lifetime(path_span)
-                }).collect();
-            }
+        if !parameters.parenthesized && parameters.lifetimes.is_empty() {
+            parameters.lifetimes = (0..expected_lifetimes).map(|_| {
+                self.elided_lifetime(path_span)
+            }).collect();
         }
 
         hir::PathSegment {
@@ -885,24 +918,38 @@ impl<'a> LoweringContext<'a> {
     fn lower_angle_bracketed_parameter_data(&mut self,
                                             data: &AngleBracketedParameterData,
                                             param_mode: ParamMode)
-                                            -> hir::AngleBracketedParameterData {
+                                            -> hir::PathParameters {
         let &AngleBracketedParameterData { ref lifetimes, ref types, ref bindings, .. } = data;
-        hir::AngleBracketedParameterData {
+        hir::PathParameters {
             lifetimes: self.lower_lifetimes(lifetimes),
             types: types.iter().map(|ty| self.lower_ty(ty)).collect(),
             infer_types: types.is_empty() && param_mode == ParamMode::Optional,
             bindings: bindings.iter().map(|b| self.lower_ty_binding(b)).collect(),
+            parenthesized: false,
         }
     }
 
     fn lower_parenthesized_parameter_data(&mut self,
                                           data: &ParenthesizedParameterData)
-                                          -> hir::ParenthesizedParameterData {
+                                          -> hir::PathParameters {
         let &ParenthesizedParameterData { ref inputs, ref output, span } = data;
-        hir::ParenthesizedParameterData {
-            inputs: inputs.iter().map(|ty| self.lower_ty(ty)).collect(),
-            output: output.as_ref().map(|ty| self.lower_ty(ty)),
-            span,
+        let inputs = inputs.iter().map(|ty| self.lower_ty(ty)).collect();
+        let mk_tup = |this: &mut Self, tys, span| {
+            P(hir::Ty { node: hir::TyTup(tys), id: this.next_id().node_id, span })
+        };
+
+        hir::PathParameters {
+            lifetimes: hir::HirVec::new(),
+            types: hir_vec![mk_tup(self, inputs, span)],
+            infer_types: false,
+            bindings: hir_vec![hir::TypeBinding {
+                id: self.next_id().node_id,
+                name: Symbol::intern(FN_OUTPUT_NAME),
+                ty: output.as_ref().map(|ty| self.lower_ty(&ty))
+                                   .unwrap_or_else(|| mk_tup(self, hir::HirVec::new(), span)),
+                span: output.as_ref().map_or(span, |ty| ty.span),
+            }],
+            parenthesized: true,
         }
     }
 
@@ -1877,7 +1924,8 @@ impl<'a> LoweringContext<'a> {
                 hir::ExprCall(f, args.iter().map(|x| self.lower_expr(x)).collect())
             }
             ExprKind::MethodCall(ref seg, ref args) => {
-                let hir_seg = self.lower_path_segment(e.span, seg, ParamMode::Optional, 0);
+                let hir_seg = self.lower_path_segment(e.span, seg, ParamMode::Optional, 0,
+                                                      ParenthesizedGenericArgs::Err);
                 let args = args.iter().map(|x| self.lower_expr(x)).collect();
                 hir::ExprMethodCall(hir_seg, seg.span, args)
             }

src/librustc/hir/mod.rs

@@ -26,7 +26,6 @@ pub use self::TyParamBound::*;
 pub use self::UnOp::*;
 pub use self::UnsafeSource::*;
 pub use self::Visibility::{Public, Inherited};
-pub use self::PathParameters::*;
 
 use hir::def::Def;
 use hir::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
@@ -227,65 +226,7 @@ impl PathSegment {
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub enum PathParameters {
-    /// The `<'a, A,B,C>` in `foo::bar::baz::<'a, A,B,C>`
-    AngleBracketedParameters(AngleBracketedParameterData),
-    /// The `(A,B)` and `C` in `Foo(A,B) -> C`
-    ParenthesizedParameters(ParenthesizedParameterData),
-}
-
-impl PathParameters {
-    pub fn none() -> PathParameters {
-        AngleBracketedParameters(AngleBracketedParameterData {
-            lifetimes: HirVec::new(),
-            types: HirVec::new(),
-            infer_types: true,
-            bindings: HirVec::new(),
-        })
-    }
-
-    /// Returns the types that the user wrote. Note that these do not necessarily map to the type
-    /// parameters in the parenthesized case.
-    pub fn types(&self) -> HirVec<&P<Ty>> {
-        match *self {
-            AngleBracketedParameters(ref data) => {
-                data.types.iter().collect()
-            }
-            ParenthesizedParameters(ref data) => {
-                data.inputs
-                    .iter()
-                    .chain(data.output.iter())
-                    .collect()
-            }
-        }
-    }
-
-    pub fn lifetimes(&self) -> HirVec<&Lifetime> {
-        match *self {
-            AngleBracketedParameters(ref data) => {
-                data.lifetimes.iter().collect()
-            }
-            ParenthesizedParameters(_) => {
-                HirVec::new()
-            }
-        }
-    }
-
-    pub fn bindings(&self) -> HirVec<&TypeBinding> {
-        match *self {
-            AngleBracketedParameters(ref data) => {
-                data.bindings.iter().collect()
-            }
-            ParenthesizedParameters(_) => {
-                HirVec::new()
-            }
-        }
-    }
-}
-
-/// A path like `Foo<'a, T>`
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub struct AngleBracketedParameterData {
+pub struct PathParameters {
     /// The lifetime parameters for this path segment.
     pub lifetimes: HirVec<Lifetime>,
     /// The type parameters for this path segment, if present.
@@ -298,19 +239,33 @@ pub struct AngleBracketedParameterData {
     /// Bindings (equality constraints) on associated types, if present.
     /// E.g., `Foo<A=Bar>`.
     pub bindings: HirVec<TypeBinding>,
+    /// Were parameters written in parenthesized form `Fn(T) -> U`?
+    /// This is required mostly for pretty-printing and diagnostics,
+    /// but also for changing lifetime elision rules to be "function-like".
+    pub parenthesized: bool,
 }
 
-/// A path like `Foo(A,B) -> C`
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub struct ParenthesizedParameterData {
-    /// Overall span
-    pub span: Span,
-
-    /// `(A,B)`
-    pub inputs: HirVec<P<Ty>>,
+impl PathParameters {
+    pub fn none() -> Self {
+        Self {
+            lifetimes: HirVec::new(),
+            types: HirVec::new(),
+            infer_types: true,
+            bindings: HirVec::new(),
+            parenthesized: false,
+        }
+    }
 
-    /// `C`
-    pub output: Option<P<Ty>>,
+    pub fn inputs(&self) -> &[P<Ty>] {
+        if self.parenthesized {
+            if let Some(ref ty) = self.types.get(0) {
+                if let TyTup(ref tys) = ty.node {
+                    return tys;
+                }
+            }
+        }
+        bug!("PathParameters::inputs: not a `Fn(T) -> U`");
+    }
 }
 
 /// The AST represents all type param bounds as types.