pkg/compiler: add check that len does not refer to array with varlen elements

This [almost] always means a bug in descriptions.
Fix all bugs identified by the check.

2 files changed, 17 insertions, 0 deletions

diff --git a/pkg/compiler/check.go b/pkg/compiler/check.go
index 5fefeaf68..349dd9017 100644
--- a/pkg/compiler/check.go
+++ b/pkg/compiler/check.go
@@ -221,6 +221,21 @@ func (comp *compiler) checkLenTarget(t *ast.Type, name, target string, fields []
 		if fld.Type == t {
 			comp.error(t.Pos, "%v target %v refer to itself", t.Ident, target)
 		}
+		if t.Ident == "len" {
+			inner := fld.Type
+			desc, args, _ := comp.getArgsBase(inner, "", prog.DirIn, false)
+			for desc == typePtr {
+				if desc != typePtr {
+					break
+				}
+				inner = args[1]
+				desc, args, _ = comp.getArgsBase(inner, "", prog.DirIn, false)
+			}
+			if desc == typeArray && comp.isVarlen(args[0]) {
+				comp.error(t.Pos, "len target %v refer to an array with"+
+					" variable-size elements (do you mean bytesize?)", target)
+			}
+		}
 		return
 	}
 	for _, parent := range parents {
diff --git a/pkg/compiler/testdata/errors2.txt b/pkg/compiler/testdata/errors2.txt
index 0292aca5e..5b418ab55 100644
--- a/pkg/compiler/testdata/errors2.txt
+++ b/pkg/compiler/testdata/errors2.txt
@@ -52,6 +52,8 @@ foo$104(a len[parent])		### len target parent does not exist
 foo$105(a ptr[in, int32], b ptr[in, array[len[a, int32]]])
 foo$106(a int32, b ptr[in, csum[a, inet, int32]])
 foo$107(a int32, b ptr[in, csum[c, inet, int32]])	### csum target c does not exist
+foo$108(a ptr[in, array[string]], b len[a])		### len target a refer to an array with variable-size elements (do you mean bytesize?)
+foo$109(a ptr[in, array[string]], b ptr[in, len[a, int32]])	###  len target a refer to an array with variable-size elements (do you mean bytesize?)
 
 s1 {
 	f1	len[s2, int32]	### len target s2 does not exist