openmp: Fix up error recovery for invalid structured bindings in OpenMP range for loops [PR105839]

The PR108503 temporary DECL_HAS_VALUE_EXPR_P clearing code can ICE
during recovery, because cp_finish_decomp when it detects errors and
reports them clears DECL_HAS_VALUE_EXPR_P, clears DECL_VALUE_EXPR and
sets TREE_TYPE of the structured binding vars to error_mark_node.
The PR108503 code had an assertion that DECL_HAS_VALUE_EXPR_P is set
so that it can clear it and restore later.

The following patch allows DECL_HAS_VALUE_EXPR_P to be unset if
type is error_mark_node and doesn't set it again in that case.

2023-03-02  Jakub Jelinek  <jakub@redhat.com>

	PR c++/105839
	* parser.cc (cp_convert_omp_range_for): Allow in assert
	decomp_first_name without DECL_HAS_VALUE_EXPR_P if it has
	error_mark_node type.
	(cp_finish_omp_range_for): Don't set DECL_HAS_VALUE_EXPR_P back
	on decls which have error_mark_node type.

	* g++.dg/gomp/pr105839-1.C: New test.
	* g++.dg/gomp/pr105839-2.C: New test.

3 files changed, 54 insertions, 2 deletions

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 1a124f5..3d6b8f2 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -43312,7 +43312,9 @@ cp_convert_omp_range_for (tree &this_pre_body, vec<tree, va_gc> *for_block,
 	     name but the DECL_VALUE_EXPR will be dependent.  Hide those
 	     from folding of other loop initializers e.g. for warning
 	     purposes until cp_finish_omp_range_for.  */
-	  gcc_checking_assert (DECL_HAS_VALUE_EXPR_P (decomp_first_name));
+	  gcc_checking_assert (DECL_HAS_VALUE_EXPR_P (decomp_first_name)
+			       || (TREE_TYPE (decomp_first_name)
+				   == error_mark_node));
 	  DECL_HAS_VALUE_EXPR_P (decomp_first_name) = 0;
 	}
       TREE_VEC_ELT (v, i + 3) = decomp_first_name;
@@ -43345,7 +43347,8 @@ cp_finish_omp_range_for (tree orig, tree begin)
 	  tree d = decomp_first_name;
 	  for (unsigned i = 0; i < decomp_cnt; i++)
 	    {
-	      DECL_HAS_VALUE_EXPR_P (d) = 1;
+	      if (TREE_TYPE (d) != error_mark_node)
+		DECL_HAS_VALUE_EXPR_P (d) = 1;
 	      d = DECL_CHAIN (d);
 	    }
 	}
diff --git a/gcc/testsuite/g++.dg/gomp/pr105839-1.C b/gcc/testsuite/g++.dg/gomp/pr105839-1.C
new file mode 100644
index 0000000..64fb6a3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/gomp/pr105839-1.C
@@ -0,0 +1,25 @@
+// PR c++/105839
+// { dg-do compile { target c++11 } }
+// { dg-options "-fopenmp" }
+
+template <typename T>
+void
+foo (const T &x)
+{
+  [&] (auto &&y)		// { dg-error "use of 'auto' in lambda parameter declaration only available with" "" { target c++11_only } }
+  {
+    #pragma omp parallel for
+    for (auto &&[v1, v2] : x)	// { dg-error "cannot decompose non-array non-class type 'const int'" }
+      ;				// { dg-error "invalid type for iteration variable" "" { target c++14 } .-1 }
+				// { dg-warning "structured bindings only available with" "" { target c++14_down } .-2 }
+  } ([]{});			// { dg-error "no match for call to" "" { target c++11_only } }
+				// { dg-error "invalid user-defined conversion from" "" { target c++11_only } .-1 }
+				// { dg-error "invalid conversion from" "" { target c++11_only } .-2 }
+}
+
+void
+bar ()
+{
+  int a[10];
+  foo (a);
+}
diff --git a/gcc/testsuite/g++.dg/gomp/pr105839-2.C b/gcc/testsuite/g++.dg/gomp/pr105839-2.C
new file mode 100644
index 0000000..fdb7595
--- /dev/null
+++ b/gcc/testsuite/g++.dg/gomp/pr105839-2.C
@@ -0,0 +1,24 @@
+// PR c++/105839
+// { dg-do compile { target c++14 } }
+// { dg-options "-fopenmp" }
+
+template <typename T>
+void
+foo (const T &x)
+{
+  [&] (auto &&y)
+  {
+    #pragma omp parallel for
+    for (auto &&[v1, v2] : x)	// { dg-warning "structured bindings only available with" "" { target c++14_down } }
+      ;
+  } ([]{});
+}
+
+struct A { int a, b; };
+
+void
+bar ()
+{
+  A a[10];
+  foo (a);
+}