Attempt to resolve pattern items in tuple pattern with a rest pattern

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc (visit(TuplePattern)): Update HAS_REST
	case to continue to attempt to resolve pattern items after emitting size error.

Signed-off-by: Yap Zhi Heng <[email protected]>

Author: Polygonalr

gcc/rust/typecheck/rust-hir-type-check-pattern.cc

@@ -657,14 +657,14 @@ TypeCheckPattern::visit (HIR::TuplePattern &pattern)
 	  {
 	    emit_pattern_size_error (pattern, par.get_fields ().size (),
 				     min_size_required);
-	    // TODO attempt to continue to do typechecking even after wrong
-	    // size
-	    break;
+	    // continue and attempt to resolve individual items in the pattern
 	  }
 
 	// Resolve lower patterns
 	std::vector<TyTy::TyVar> pattern_elems;
-	for (size_t i = 0; i < lower.size (); i++)
+	size_t nlower_items_to_resolve
+	  = std::min (lower.size (), par.get_fields ().size ());
+	for (size_t i = 0; i < nlower_items_to_resolve; i++)
 	  {
 	    auto &p = lower[i];
 	    TyTy::BaseType *par_type = par.get_field (i);
@@ -673,16 +673,23 @@ TypeCheckPattern::visit (HIR::TuplePattern &pattern)
 	    pattern_elems.emplace_back (elem->get_ref ());
 	  }
 
+	if (lower.size () > par.get_fields ().size ())
+	  break;
+
 	// Pad pattern_elems until needing to resolve upper patterns
-	size_t rest_end = par.get_fields ().size () - upper.size ();
+	size_t rest_end
+	  = std::max (par.get_fields ().size () - upper.size (), lower.size ());
 	for (size_t i = lower.size (); i < rest_end; i++)
 	  {
 	    TyTy::BaseType *par_type = par.get_field (i);
 	    pattern_elems.emplace_back (par_type->get_ref ());
 	  }
 
+	size_t nupper_items_to_resolve
+	  = std::min (upper.size (),
+		      par.get_fields ().size () - pattern_elems.size ());
 	// Resolve upper patterns
-	for (size_t i = 0; i < upper.size (); i++)
+	for (size_t i = 0; i < nupper_items_to_resolve; i++)
 	  {
 	    auto &p = upper[i];
 	    TyTy::BaseType *par_type = par.get_field (rest_end + i);

gcc/testsuite/rust/compile/tuplepattern-restpattern-typecheck-err.rs

@@ -0,0 +1,8 @@
+fn main() {
+    match (1, 2.2, "not 3") {
+        // { dg-error "expected a tuple with 3 elements, found one with 5 elements" "" { target *-*-* } .+1 }
+        (a, b, .., c, d, e) => {
+            let _ = b + c; // { dg-error "cannot apply operator .+. to types <float> and & str" }
+        }
+    }
+}