librustc: Check structure constructors against their types.

This breaks code like:

    struct Point<T> {
        x: T,
        y: T,
    }

    let pt = Point::<bool> {
        x: 1,
        y: 2,
    };

Change this code to not contain a type error. For example:

    let pt = Point::<int> {
        x: 1,
        y: 2,
    };

Closes #9620.
Closes #15875.

[breaking-change]

Author: pcwalton

src/librustc/middle/typeck/astconv.rs

@@ -53,6 +53,7 @@ use middle::const_eval;
 use middle::def;
 use middle::lang_items::FnMutTraitLangItem;
 use middle::subst::{FnSpace, TypeSpace, SelfSpace, Subst, Substs};
+use middle::subst::{VecPerParamSpace};
 use middle::ty;
 use middle::ty_fold::TypeFolder;
 use middle::typeck::rscope::{ExplicitRscope, ImpliedSingleRscope};
@@ -299,6 +300,47 @@ pub fn ast_path_to_ty<AC:AstConv,RS:RegionScope>(
     TypeAndSubsts { substs: substs, ty: ty }
 }
 
+/// Returns the type that this AST path refers to. If the path has no type
+/// parameters and the corresponding type has type parameters, fresh type
+/// and/or region variables are substituted.
+///
+/// This is used when checking the constructor in struct literals.
+pub fn ast_path_to_ty_relaxed<AC:AstConv,
+                              RS:RegionScope>(
+                              this: &AC,
+                              rscope: &RS,
+                              did: ast::DefId,
+                              path: &ast::Path)
+                              -> TypeAndSubsts {
+    let tcx = this.tcx();
+    let ty::Polytype {
+        generics: generics,
+        ty: decl_ty
+    } = this.get_item_ty(did);
+
+    let substs = if (generics.has_type_params(TypeSpace) ||
+        generics.has_region_params(TypeSpace)) &&
+            path.segments.iter().all(|s| {
+                s.lifetimes.len() == 0 && s.types.len() == 0
+            }) {
+        let type_params = Vec::from_fn(generics.types.len(TypeSpace),
+                                       |_| this.ty_infer(path.span));
+        let region_params =
+            rscope.anon_regions(path.span, generics.regions.len(TypeSpace))
+                  .unwrap();
+        Substs::new(VecPerParamSpace::params_from_type(type_params),
+                    VecPerParamSpace::params_from_type(region_params))
+    } else {
+        ast_path_substs(this, rscope, &generics, None, path)
+    };
+
+    let ty = decl_ty.subst(tcx, &substs);
+    TypeAndSubsts {
+        substs: substs,
+        ty: ty,
+    }
+}
+
 pub static NO_REGIONS: uint = 1;
 pub static NO_TPS: uint = 2;
 

src/librustc/middle/typeck/check/mod.rs

@@ -3416,10 +3416,11 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
       ast::ExprStruct(ref path, ref fields, base_expr) => {
         // Resolve the path.
         let def = tcx.def_map.borrow().find(&id).map(|i| *i);
-        match def {
+        let struct_id = match def {
             Some(def::DefVariant(enum_id, variant_id, _)) => {
                 check_struct_enum_variant(fcx, id, expr.span, enum_id,
                                           variant_id, fields.as_slice());
+                enum_id
             }
             Some(def) => {
                 // Verify that this was actually a struct.
@@ -3439,11 +3440,47 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
                             pprust::path_to_string(path));
                     }
                 }
+
+                def.def_id()
             }
             _ => {
                 tcx.sess.span_bug(path.span,
                                   "structure constructor wasn't resolved")
             }
+        };
+
+        // Turn the path into a type and verify that that type unifies with
+        // the resulting structure type. This is needed to handle type
+        // parameters correctly.
+        let actual_structure_type = fcx.expr_ty(&*expr);
+        if !ty::type_is_error(actual_structure_type) {
+            let type_and_substs = astconv::ast_path_to_ty_relaxed(fcx,
+                                                                  fcx.infcx(),
+                                                                  struct_id,
+                                                                  path);
+            match fcx.mk_subty(false,
+                               infer::Misc(path.span),
+                               actual_structure_type,
+                               type_and_substs.ty) {
+                Ok(()) => {}
+                Err(type_error) => {
+                    let type_error_description =
+                        ty::type_err_to_str(tcx, &type_error);
+                    fcx.tcx()
+                       .sess
+                       .span_err(path.span,
+                                 format!("structure constructor specifies a \
+                                         structure of type `{}`, but this \
+                                         structure has type `{}`: {}",
+                                         fcx.infcx()
+                                            .ty_to_string(type_and_substs.ty),
+                                         fcx.infcx()
+                                            .ty_to_string(
+                                                actual_structure_type),
+                                         type_error_description).as_slice());
+                    ty::note_and_explain_type_err(tcx, &type_error);
+                }
+            }
         }
       }
       ast::ExprField(ref base, ref field, ref tys) => {

src/test/compile-fail/structure-constructor-type-mismatch.rs

@@ -0,0 +1,56 @@
+// Copyright 2014 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.
+
+struct Point<T> {
+    x: T,
+    y: T,
+}
+
+type PointF = Point<f32>;
+
+struct Pair<T,U> {
+    x: T,
+    y: U,
+}
+
+type PairF<U> = Pair<f32,U>;
+
+fn main() {
+    let pt = PointF {
+        //~^ ERROR expected f32 but found int
+        x: 1i,
+        y: 2i,
+    };
+
+    let pt2 = Point::<f32> {
+        //~^ ERROR expected f32 but found int
+        x: 3i,
+        y: 4i,
+    };
+
+    let pair = PairF {
+        //~^ ERROR expected f32 but found int
+        x: 5i,
+        y: 6i,
+    };
+
+    let pair2 = PairF::<int> {
+        //~^ ERROR expected f32 but found int
+        x: 7i,
+        y: 8i,
+    };
+
+    let pt3 = PointF::<int> {
+        //~^ ERROR wrong number of type arguments
+        x: 9i,
+        y: 10i,
+    };
+}
+