gccrs: Add mechanism use pattern information to improve type info

When we have an untyped closure we assumed all parameters were inference
variables but we can use the pattern type to try and improve the type info
so if we have a reference pattern it must be a reference to an inference
variables '&_'. This patch adds a new visitor to figure this out for
untyped closure parameters.

Note this test case does fully type resolve into the gimple:

    bool test::main::{{closure}}
        (struct test::main::{{closure}} $closure, struct (& u8) args)
    { ... }

Though the Rustc version does fail type-resolution but we make some
assumptions during comparison expressions here that they resolve to a bool
this will change when we implement the comparison lang items.

Fixes #2142

gcc/rust/ChangeLog:

	* hir/tree/rust-hir-pattern.h: add missing get_mutability
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit):
	use new ClosureParamInfer on untyped parameters
	* typecheck/rust-hir-type-check-pattern.cc (ClosureParamInfer::Resolve): interface
	(ClosureParamInfer::ClosureParamInfer): constructor
	(ClosureParamInfer::visit): visitors for each pattern
	* typecheck/rust-hir-type-check-pattern.h (class ClosureParamInfer): new visitor

gcc/testsuite/ChangeLog:

	* rust/compile/issue-2142.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

5 files changed, 159 insertions, 13 deletions

diff --git a/gcc/rust/hir/tree/rust-hir-pattern.h b/gcc/rust/hir/tree/rust-hir-pattern.h
index f6359f9..5fa9a17 100644
--- a/gcc/rust/hir/tree/rust-hir-pattern.h
+++ b/gcc/rust/hir/tree/rust-hir-pattern.h
@@ -462,6 +462,8 @@ public:
 
   bool is_mut () const { return mut == Mutability::Mut; }
 
+  Mutability get_mutability () const { return mut; }
+
   void accept_vis (HIRFullVisitor &vis) override;
   void accept_vis (HIRPatternVisitor &vis) override;
 
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.cc b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
index f822048..3dafcd2 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
@@ -1471,25 +1471,20 @@ TypeCheckExpr::visit (HIR::ClosureExpr &expr)
   std::vector<TyTy::TyVar> parameter_types;
   for (auto &p : expr.get_params ())
     {
+      TyTy::BaseType *param_tyty = nullptr;
       if (p.has_type_given ())
 	{
-	  TyTy::BaseType *param_tyty
-	    = TypeCheckType::Resolve (p.get_type ().get ());
-	  TyTy::TyVar param_ty (param_tyty->get_ref ());
-	  parameter_types.push_back (param_ty);
-
-	  TypeCheckPattern::Resolve (p.get_pattern ().get (),
-				     param_ty.get_tyty ());
+	  param_tyty = TypeCheckType::Resolve (p.get_type ().get ());
 	}
       else
 	{
-	  TyTy::TyVar param_ty
-	    = TyTy::TyVar::get_implicit_infer_var (p.get_locus ());
-	  parameter_types.push_back (param_ty);
-
-	  TypeCheckPattern::Resolve (p.get_pattern ().get (),
-				     param_ty.get_tyty ());
+	  param_tyty = ClosureParamInfer::Resolve (p.get_pattern ().get ());
 	}
+
+      TyTy::TyVar param_ty (param_tyty->get_ref ());
+      parameter_types.push_back (param_ty);
+
+      TypeCheckPattern::Resolve (p.get_pattern ().get (), param_ty.get_tyty ());
     }
 
   // we generate an implicit hirid for the closure args
diff --git a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
index bde7076..1221bcc 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
@@ -447,5 +447,116 @@ TypeCheckPattern::visit (HIR::AltPattern &pattern)
 		 "type checking alternate patterns not supported");
 }
 
+TyTy::BaseType *
+ClosureParamInfer::Resolve (HIR::Pattern *pattern)
+{
+  ClosureParamInfer resolver;
+  pattern->accept_vis (resolver);
+
+  if (resolver.infered->get_kind () != TyTy::TypeKind::ERROR)
+    {
+      resolver.context->insert_implicit_type (resolver.infered);
+      resolver.mappings->insert_location (resolver.infered->get_ref (),
+					  pattern->get_locus ());
+    }
+  return resolver.infered;
+}
+
+ClosureParamInfer::ClosureParamInfer ()
+  : TypeCheckBase (), infered (new TyTy::ErrorType (0))
+{}
+
+void
+ClosureParamInfer::visit (HIR::WildcardPattern &pattern)
+{
+  HirId id = pattern.get_pattern_mappings ().get_hirid ();
+  infered = new TyTy::InferType (id, TyTy::InferType::InferTypeKind::GENERAL,
+				 TyTy::InferType::TypeHint::Default (),
+				 pattern.get_locus ());
+}
+
+void
+ClosureParamInfer::visit (HIR::IdentifierPattern &pattern)
+{
+  HirId id = pattern.get_pattern_mappings ().get_hirid ();
+  infered = new TyTy::InferType (id, TyTy::InferType::InferTypeKind::GENERAL,
+				 TyTy::InferType::TypeHint::Default (),
+				 pattern.get_locus ());
+}
+
+void
+ClosureParamInfer::visit (HIR::ReferencePattern &pattern)
+{
+  TyTy::BaseType *element
+    = ClosureParamInfer::Resolve (pattern.get_referenced_pattern ().get ());
+
+  HirId id = pattern.get_pattern_mappings ().get_hirid ();
+  infered = new TyTy::ReferenceType (id, TyTy::TyVar (element->get_ref ()),
+				     pattern.get_mutability ());
+}
+
+void
+ClosureParamInfer::visit (HIR::PathInExpression &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::StructPattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::TupleStructPattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::TuplePattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::LiteralPattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::RangePattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::QualifiedPathInExpression &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::SlicePattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
+void
+ClosureParamInfer::visit (HIR::AltPattern &pattern)
+{
+  rust_sorry_at (pattern.get_locus (),
+		 "unable to infer this kind of parameter pattern");
+}
+
 } // namespace Resolver
 } // namespace Rust
diff --git a/gcc/rust/typecheck/rust-hir-type-check-pattern.h b/gcc/rust/typecheck/rust-hir-type-check-pattern.h
index 93afe69..4bf371f 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-pattern.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-pattern.h
@@ -58,6 +58,30 @@ private:
   TyTy::BaseType *infered;
 };
 
+class ClosureParamInfer : private TypeCheckBase, private HIR::HIRPatternVisitor
+{
+public:
+  static TyTy::BaseType *Resolve (HIR::Pattern *pattern);
+
+  void visit (HIR::PathInExpression &pattern) override;
+  void visit (HIR::StructPattern &pattern) override;
+  void visit (HIR::TupleStructPattern &pattern) override;
+  void visit (HIR::WildcardPattern &pattern) override;
+  void visit (HIR::TuplePattern &pattern) override;
+  void visit (HIR::LiteralPattern &pattern) override;
+  void visit (HIR::RangePattern &pattern) override;
+  void visit (HIR::IdentifierPattern &pattern) override;
+  void visit (HIR::QualifiedPathInExpression &pattern) override;
+  void visit (HIR::ReferencePattern &pattern) override;
+  void visit (HIR::SlicePattern &pattern) override;
+  void visit (HIR::AltPattern &pattern) override;
+
+private:
+  ClosureParamInfer ();
+
+  TyTy::BaseType *infered;
+};
+
 } // namespace Resolver
 } // namespace Rust
 
diff --git a/gcc/testsuite/rust/compile/issue-2142.rs b/gcc/testsuite/rust/compile/issue-2142.rs
new file mode 100644
index 0000000..7a8bb2a
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2142.rs
@@ -0,0 +1,14 @@
+#[lang = "fn_once"]
+pub trait FnOnce<Args> {
+    #[lang = "fn_once_output"]
+    type Output;
+
+    extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
+}
+
+fn main() {
+    let lambda = |&c| c != b'9';
+
+    let a = b'1';
+    lambda(&a);
+}