compiler: prohibit homonymous flags and consts

Since both flags and consts can be used as type-options for integers, we
want to avoid ambiguity by preventing a flag and a const from having the
same name.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

pkg/compiler/check.go

@@ -25,7 +25,7 @@ func (comp *compiler) typecheck() {
 	comp.checkTypes()
 }
 
-func (comp *compiler) check() {
+func (comp *compiler) check(consts map[string]uint64) {
 	comp.checkTypeValues()
 	comp.checkAttributeValues()
 	comp.checkUnused()
@@ -34,6 +34,7 @@ func (comp *compiler) check() {
 	comp.checkConstructors()
 	comp.checkVarlens()
 	comp.checkDupConsts()
+	comp.checkConstsFlags(consts)
 }
 
 func (comp *compiler) checkComments() {
@@ -660,6 +661,15 @@ func (comp *compiler) checkUnused() {
 	}
 }
 
+func (comp *compiler) checkConstsFlags(consts map[string]uint64) {
+	for name := range consts {
+		if flags, isFlag := comp.intFlags[name]; isFlag {
+			pos, _, _ := flags.Info()
+			comp.error(pos, "const %v is already a flag", name)
+		}
+	}
+}
+
 type structDir struct {
 	Struct string
 	Dir    prog.Dir

pkg/compiler/compiler.go

@@ -93,7 +93,7 @@ func Compile(desc *ast.Description, consts map[string]uint64, target *targets.Ta
 		comp.assignSyscallNumbers(consts)
 	}
 	comp.patchConsts(consts)
-	comp.check()
+	comp.check(consts)
 	if comp.errors != 0 {
 		return nil
 	}

pkg/compiler/testdata/errors2.txt

@@ -383,6 +383,9 @@ type type500 proc[C1, 8, int8]	### values starting from 1 with step 8 overflow b
 type type501 int8		### unused type type501
 type type502[C] const[C, int8]	### unused type type502
 
+C2 = 0, 1, 2			### const C2 is already a flag
+use_flags(a flags[C2])
+
 s405 {
 	f1	int16:8[-256:0]		### int range [18446744073709551360:0] is too large for base type of size 8
 	f2	int16:8[0:256]		### int range [0:256] is too large for base type of size 8