compiler: error on circular dependencies in flag definitions

To detect those circular dependencies, we simply keep track of which
flags we already visited when flattening the flags definition.

Suggested-by: Aleksandr Nogikh <nogikh@google.com>
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

2 files changed, 16 insertions, 3 deletions

diff --git a/pkg/compiler/compiler.go b/pkg/compiler/compiler.go
index 3c5dea1d1..2e13988b7 100644
--- a/pkg/compiler/compiler.go
+++ b/pkg/compiler/compiler.go
@@ -361,7 +361,7 @@ func arrayContains(a []string, v string) bool {
 
 func (comp *compiler) flattenFlags() {
 	for name, flags := range comp.intFlags {
-		if err := comp.recurFlattenFlags(name, flags); err != nil {
+		if err := comp.recurFlattenFlags(name, flags, map[string]bool{}); err != nil {
 			comp.error(flags.Pos, "%v", err)
 		}
 	}
@@ -379,11 +379,18 @@ func (comp *compiler) flattenFlags() {
 	}
 }
 
-func (comp *compiler) recurFlattenFlags(name string, flags *ast.IntFlags) error {
+func (comp *compiler) recurFlattenFlags(name string, flags *ast.IntFlags, visitedFlags map[string]bool) error {
+	if _, visited := visitedFlags[name]; visited {
+		return fmt.Errorf("flags %v used twice or circular dependency on %v", name, name)
+	}
+	visitedFlags[name] = true
+
 	var values []*ast.Int
 	for _, flag := range flags.Values {
 		if f, isFlags := comp.intFlags[flag.Ident]; isFlags {
-			comp.recurFlattenFlags(flag.Ident, f)
+			if err := comp.recurFlattenFlags(flag.Ident, f, visitedFlags); err != nil {
+				return err
+			}
 			values = append(values, comp.intFlags[flag.Ident].Values...)
 		} else {
 			values = append(values, flag)
diff --git a/pkg/compiler/testdata/errors.txt b/pkg/compiler/testdata/errors.txt
index 321ff8daf..47d343e36 100644
--- a/pkg/compiler/testdata/errors.txt
+++ b/pkg/compiler/testdata/errors.txt
@@ -97,6 +97,12 @@ f3000 = 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011,
 
 nested_flags(a flags[f1000], b flags[f1100])
 
+f110 = 1, 2, 3, 4, f120		### flags f110 used twice or circular dependency on f110
+f120 = 10, 11, 12, f130		### flags f120 used twice or circular dependency on f120
+f130 = 100, 110, f110		### flags f130 used twice or circular dependency on f130
+
+loop_flags(a flags[f110])
+
 resource r2[r0]: 2
 resource r3[int32:1]		### unexpected ':', only struct fields can be bitfields
 resource r4[int32[opt]]		### resource base can't be marked as opt