fix: branch stmts (gnolang#3043)

Adds validation for `break`, `continue` and `fallthrough` to disallow
invalid code.
Moves existing validation from the runtime to the preprocessor.

Closes gnolang#2973

gnovm/pkg/gnolang/nodes.go

@@ -149,16 +149,17 @@ func (loc Location) IsZero() bool {
 type GnoAttribute string
 
 const (
-	ATTR_PREPROCESSED  GnoAttribute = "ATTR_PREPROCESSED"
-	ATTR_PREDEFINED    GnoAttribute = "ATTR_PREDEFINED"
-	ATTR_TYPE_VALUE    GnoAttribute = "ATTR_TYPE_VALUE"
-	ATTR_TYPEOF_VALUE  GnoAttribute = "ATTR_TYPEOF_VALUE"
-	ATTR_IOTA          GnoAttribute = "ATTR_IOTA"
-	ATTR_LOCATIONED    GnoAttribute = "ATTR_LOCATIONE"     // XXX DELETE
-	ATTR_GOTOLOOP_STMT GnoAttribute = "ATTR_GOTOLOOP_STMT" // XXX delete?
-	ATTR_LOOP_DEFINES  GnoAttribute = "ATTR_LOOP_DEFINES"  // []Name defined within loops.
-	ATTR_LOOP_USES     GnoAttribute = "ATTR_LOOP_USES"     // []Name loop defines actually used.
-	ATTR_SHIFT_RHS     GnoAttribute = "ATTR_SHIFT_RHS"
+	ATTR_PREPROCESSED    GnoAttribute = "ATTR_PREPROCESSED"
+	ATTR_PREDEFINED      GnoAttribute = "ATTR_PREDEFINED"
+	ATTR_TYPE_VALUE      GnoAttribute = "ATTR_TYPE_VALUE"
+	ATTR_TYPEOF_VALUE    GnoAttribute = "ATTR_TYPEOF_VALUE"
+	ATTR_IOTA            GnoAttribute = "ATTR_IOTA"
+	ATTR_LOCATIONED      GnoAttribute = "ATTR_LOCATIONE"     // XXX DELETE
+	ATTR_GOTOLOOP_STMT   GnoAttribute = "ATTR_GOTOLOOP_STMT" // XXX delete?
+	ATTR_LOOP_DEFINES    GnoAttribute = "ATTR_LOOP_DEFINES"  // []Name defined within loops.
+	ATTR_LOOP_USES       GnoAttribute = "ATTR_LOOP_USES"     // []Name loop defines actually used.
+	ATTR_SHIFT_RHS       GnoAttribute = "ATTR_SHIFT_RHS"
+	ATTR_LAST_BLOCK_STMT GnoAttribute = "ATTR_LAST_BLOCK_STMT"
 )
 
 type Attributes struct {

gnovm/pkg/gnolang/op_exec.go

@@ -676,25 +676,15 @@ EXEC_SWITCH:
 			bs.Active = bs.Body[cs.BodyIndex] // prefill
 		case FALLTHROUGH:
 			ss, ok := m.LastFrame().Source.(*SwitchStmt)
+			// this is handled in the preprocessor
+			// should never happen
 			if !ok {
-				// fallthrough is only allowed in a switch statement
 				panic("fallthrough statement out of place")
 			}
-			if ss.IsTypeSwitch {
-				// fallthrough is not allowed in type switches
-				panic("cannot fallthrough in type switch")
-			}
+
 			b := m.LastBlock()
-			if b.bodyStmt.NextBodyIndex != len(b.bodyStmt.Body) {
-				// fallthrough is not the final statement
-				panic("fallthrough statement out of place")
-			}
 			// compute next switch clause from BodyIndex (assigned in preprocess)
 			nextClause := cs.BodyIndex + 1
-			if nextClause >= len(ss.Clauses) {
-				// no more clause after the one executed, this is not allowed
-				panic("cannot fallthrough final case in switch")
-			}
 			// expand block size
 			cl := ss.Clauses[nextClause]
 			if nn := cl.GetNumNames(); int(nn) > len(b.Values) {

gnovm/pkg/gnolang/preprocess.go

@@ -298,6 +298,11 @@ func initStaticBlocks(store Store, ctx BlockNode, bn BlockNode) {
 					last.Predefine(false, n.VarName)
 				}
 			case *SwitchClauseStmt:
+				blen := len(n.Body)
+				if blen > 0 {
+					n.Body[blen-1].SetAttribute(ATTR_LAST_BLOCK_STMT, true)
+				}
+
 				// parent switch statement.
 				ss := ns[len(ns)-1].(*SwitchStmt)
 				// anything declared in ss are copied,
@@ -2137,9 +2142,7 @@ func preprocess1(store Store, ctx BlockNode, n Node) Node {
 				switch n.Op {
 				case BREAK:
 					if n.Label == "" {
-						if !findBreakableNode(ns) {
-							panic("cannot break with no parent loop or switch")
-						}
+						findBreakableNode(last, store)
 					} else {
 						// Make sure that the label exists, either for a switch or a
 						// BranchStmt.
@@ -2149,9 +2152,7 @@ func preprocess1(store Store, ctx BlockNode, n Node) Node {
 					}
 				case CONTINUE:
 					if n.Label == "" {
-						if !findContinuableNode(ns) {
-							panic("cannot continue with no parent loop")
-						}
+						findContinuableNode(last, store)
 					} else {
 						if isSwitchLabel(ns, n.Label) {
 							panic(fmt.Sprintf("invalid continue label %q\n", n.Label))
@@ -2163,17 +2164,36 @@ func preprocess1(store Store, ctx BlockNode, n Node) Node {
 					n.Depth = depth
 					n.BodyIndex = index
 				case FALLTHROUGH:
-					if swchC, ok := last.(*SwitchClauseStmt); ok {
-						// last is a switch clause, find its index in the switch and assign
-						// it to the fallthrough node BodyIndex. This will be used at
-						// runtime to determine the next switch clause to run.
-						swch := lastSwitch(ns)
-						for i := range swch.Clauses {
-							if &swch.Clauses[i] == swchC {
-								// switch clause found
-								n.BodyIndex = i
-								break
-							}
+					swchC, ok := last.(*SwitchClauseStmt)
+					if !ok {
+						// fallthrough is only allowed in a switch statement
+						panic("fallthrough statement out of place")
+					}
+
+					if n.GetAttribute(ATTR_LAST_BLOCK_STMT) != true {
+						// no more clause after the one executed, this is not allowed
+						panic("fallthrough statement out of place")
+					}
+
+					// last is a switch clause, find its index in the switch and assign
+					// it to the fallthrough node BodyIndex. This will be used at
+					// runtime to determine the next switch clause to run.
+					swch := lastSwitch(ns)
+
+					if swch.IsTypeSwitch {
+						// fallthrough is not allowed in type switches
+						panic("cannot fallthrough in type switch")
+					}
+
+					for i := range swch.Clauses {
+						if i == len(swch.Clauses)-1 {
+							panic("cannot fallthrough final case in switch")
+						}
+
+						if &swch.Clauses[i] == swchC {
+							// switch clause found
+							n.BodyIndex = i
+							break
 						}
 					}
 				default:
@@ -3272,24 +3292,36 @@ func funcOf(last BlockNode) (BlockNode, *FuncTypeExpr) {
 	}
 }
 
-func findBreakableNode(ns []Node) bool {
-	for _, n := range ns {
-		switch n.(type) {
-		case *ForStmt, *RangeStmt, *SwitchClauseStmt:
-			return true
+func findBreakableNode(last BlockNode, store Store) {
+	for last != nil {
+		switch last.(type) {
+		case *FuncLitExpr, *FuncDecl:
+			panic("break statement out of place")
+		case *ForStmt:
+			return
+		case *RangeStmt:
+			return
+		case *SwitchClauseStmt:
+			return
 		}
+
+		last = last.GetParentNode(store)
 	}
-	return false
 }
 
-func findContinuableNode(ns []Node) bool {
-	for _, n := range ns {
-		switch n.(type) {
-		case *ForStmt, *RangeStmt:
-			return true
+func findContinuableNode(last BlockNode, store Store) {
+	for last != nil {
+		switch last.(type) {
+		case *FuncLitExpr, *FuncDecl:
+			panic("continue statement out of place")
+		case *ForStmt:
+			return
+		case *RangeStmt:
+			return
 		}
+
+		last = last.GetParentNode(store)
 	}
-	return false
 }
 
 func findBranchLabel(last BlockNode, label Name) (

gnovm/tests/files/break0.gno

@@ -5,4 +5,4 @@ func main() {
 }
 
 // Error:
-// main/files/break0.gno:4:2: cannot break with no parent loop or switch
+// main/files/break0.gno:4:2: break statement out of place

gnovm/tests/files/cont3.gno

@@ -5,4 +5,4 @@ func main() {
 }
 
 // Error:
-// main/files/cont3.gno:4:2: cannot continue with no parent loop
+// main/files/cont3.gno:4:2: continue statement out of place

gnovm/tests/files/for21.gno

@@ -0,0 +1,17 @@
+package main
+
+func main() {
+    for i := 0; i < 10; i++ {
+        if i == 1 {
+            _ = func() int {
+                continue
+                return 11
+            }()
+        }
+        println(i)
+    }
+    println("wat???")
+}
+
+// Error:
+// main/files/for21.gno:7:17: continue statement out of place

gnovm/tests/files/for22.gno

@@ -0,0 +1,17 @@
+package main
+
+func main() {
+    for i := 0; i < 10; i++ {
+        if i == 1 {
+            _ = func() int {
+                fallthrough
+                return 11
+            }()
+        }
+        println(i)
+    }
+    println("wat???")
+}
+
+// Error:
+// main/files/for22.gno:7:17: fallthrough statement out of place

gnovm/tests/files/for23.gno

@@ -0,0 +1,17 @@
+package main
+
+func main() {
+    for i := 0; i < 10; i++ {
+        if i == 1 {
+            _ = func() int {
+                break
+                return 11
+            }()
+        }
+        println(i)
+    }
+    println("wat???")
+}
+
+// Error:
+// main/files/for23.gno:7:17: break statement out of place

gnovm/tests/files/for24.gno

@@ -0,0 +1,19 @@
+package main
+
+func main() {
+    for i := 0; i < 10; i++ {
+        if i == 1 {
+            _ = func() int {
+                if true {
+                    break
+                }
+                return 11
+            }()
+        }
+        println(i)
+    }
+    println("wat???")
+}
+
+// Error:
+// main/files/for24.gno:8:21: break statement out of place

gnovm/tests/files/switch8.gno

@@ -7,4 +7,4 @@ func main() {
 }
 
 // Error:
-// fallthrough statement out of place
+// main/files/switch8.gno:5:2: fallthrough statement out of place

gnovm/tests/files/switch8b.gno

@@ -12,4 +12,4 @@ func main() {
 }
 
 // Error:
-// cannot fallthrough final case in switch
+// main/files/switch8b.gno:10:3: cannot fallthrough final case in switch

gnovm/tests/files/switch8c.gno

@@ -12,4 +12,4 @@ func main() {
 }
 
 // Error:
-// fallthrough statement out of place
+// main/files/switch8c.gno:7:3: fallthrough statement out of place

gnovm/tests/files/switch9.gno

@@ -13,4 +13,4 @@ func main() {
 }
 
 // Error:
-// cannot fallthrough in type switch
+// main/files/switch9.gno:9:3: cannot fallthrough in type switch