Add length checking for tuple patterns

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc (TypeCheckPattern::visit):
		Add length checking for tuple patterns.
	(TypeCheckPattern::emit_pattern_size_error): New function.
	* typecheck/rust-hir-type-check-pattern.h: New function
		emit_pattern_size_error.

gcc/testsuite/ChangeLog:

	* rust/compile/tuple_mismatch.rs: New test.

Signed-off-by: Nikos Alexandris <nikos-alexandris@protonmail.com>

3 files changed, 55 insertions, 8 deletions

diff --git a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
index 65a3e67..b7412bc 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-pattern.cc
@@ -262,16 +262,30 @@ TypeCheckPattern::visit (HIR::TuplePattern &pattern)
 	  = *static_cast<HIR::TuplePatternItemsMultiple *> (
 	    pattern.get_items ().get ());
 
+	if (parent->get_kind () != TyTy::TUPLE)
+	  {
+	    rust_error_at (pattern.get_locus (), "expected %s, found tuple",
+			   parent->as_string ().c_str ());
+	    break;
+	  }
+
+	const auto &patterns = ref.get_patterns ();
+	size_t nitems_to_resolve = patterns.size ();
+
+	TyTy::TupleType &par = *static_cast<TyTy::TupleType *> (parent);
+	if (patterns.size () != par.get_fields ().size ())
+	  {
+	    emit_pattern_size_error (pattern, par.get_fields ().size (),
+				     patterns.size ());
+	    nitems_to_resolve
+	      = std::min (nitems_to_resolve, par.get_fields ().size ());
+	  }
+
 	std::vector<TyTy::TyVar> pattern_elems;
-	for (size_t i = 0; i < ref.get_patterns ().size (); i++)
+	for (size_t i = 0; i < nitems_to_resolve; i++)
 	  {
-	    auto &p = ref.get_patterns ()[i];
-	    TyTy::BaseType *par_type = parent;
-	    if (parent->get_kind () == TyTy::TUPLE)
-	      {
-		TyTy::TupleType &par = *static_cast<TyTy::TupleType *> (parent);
-		par_type = par.get_field (i);
-	      }
+	    auto &p = patterns[i];
+	    TyTy::BaseType *par_type = par.get_field (i);
 
 	    TyTy::BaseType *elem
 	      = TypeCheckPattern::Resolve (p.get (), par_type);
@@ -407,5 +421,21 @@ TypeCheckPattern::visit (HIR::SlicePattern &pattern)
 		 "type checking qualified path patterns not supported");
 }
 
+void
+TypeCheckPattern::emit_pattern_size_error (const HIR::Pattern &pattern,
+					   size_t expected_field_count,
+					   size_t got_field_count)
+{
+  RichLocation r (pattern.get_locus ());
+  r.add_range (mappings->lookup_location (parent->get_ref ()));
+  rust_error_at (r,
+		 "expected a tuple with %lu %s, found one "
+		 "with %lu %s",
+		 (unsigned long) expected_field_count,
+		 expected_field_count == 1 ? "element" : "elements",
+		 (unsigned long) got_field_count,
+		 got_field_count == 1 ? "element" : "elements");
+}
+
 } // 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 e755007..a4fbf88 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-pattern.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-pattern.h
@@ -51,6 +51,10 @@ private:
 				 Analysis::NodeMapping mappings,
 				 Location locus);
 
+  void emit_pattern_size_error (const HIR::Pattern &pattern,
+				size_t expected_field_count,
+				size_t got_field_count);
+
   TyTy::BaseType *parent;
   TyTy::BaseType *infered;
 };
diff --git a/gcc/testsuite/rust/compile/tuple_mismatch.rs b/gcc/testsuite/rust/compile/tuple_mismatch.rs
new file mode 100644
index 0000000..fbeb4b2
--- /dev/null
+++ b/gcc/testsuite/rust/compile/tuple_mismatch.rs
@@ -0,0 +1,13 @@
+fn main() {
+    let (_,) = 1; // { dg-error "expected <integer>, found tuple" }
+    let (_,) = (1, 2); // { dg-error "expected a tuple with 2 elements, found one with 1 element" }
+    let (_, _) = (1, 2, 3); // { dg-error "expected a tuple with 3 elements, found one with 2 elements" }
+    let (_, _) = (1,); // { dg-error "expected a tuple with 1 element, found one with 2 elements" }
+}
+
+// The lhs and rhs sizes don't match, but we still resolve 'a' to be bool, we don't
+// error out immediately once we notice the size mismatch.
+fn foo() -> i32 { // { dg-error "expected .i32. got .bool." }
+    let (a, _) = (true, 2, 3); // { dg-error "expected a tuple with 3 elements, found one with 2 elements" }
+    a
+}