code review 7437049: go/types: "missing return" check

src/pkg/go/types/return.go

Index: src/pkg/go/types/return.go
===================================================================
new file mode 100644
--- /dev/null
+++ b/src/pkg/go/types/return.go
@@ -0,0 +1,186 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements isTerminating.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// isTerminating reports if s is a terminating statement.
+// If s is labeled, label is the label name; otherwise s
+// is "".
+func (check *checker) isTerminating(s ast.Stmt, label string) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.SendStmt,
+		*ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt, *ast.DeferStmt,
+		*ast.RangeStmt:
+		// no chance
+
+	case *ast.LabeledStmt:
+		return check.isTerminating(s.Stmt, s.Label.Name)
+
+	case *ast.ExprStmt:
+		// the predeclared panic() function is terminating
+		if call, _ := s.X.(*ast.CallExpr); call != nil {
+			if id, _ := call.Fun.(*ast.Ident); id != nil {
+				if obj := check.lookup(id); obj != nil {
+					// TODO(gri) Predeclared functions should be modelled as objects
+					//           rather then ordinary functions that have a predeclared
+					//           function type. This would simplify code here and else-
+					//           where.
+					if f, _ := obj.(*Func); f != nil && f.Type == predeclaredFunctions[_Panic] {
+						return true
+					}
+				}
+			}
+		}
+
+	case *ast.ReturnStmt:
+		return true
+
+	case *ast.BranchStmt:
+		if s.Tok == token.GOTO || s.Tok == token.FALLTHROUGH {
+			return true
+		}
+
+	case *ast.BlockStmt:
+		return check.isTerminatingList(s.List, "")
+
+	case *ast.IfStmt:
+		if s.Else != nil &&
+			check.isTerminating(s.Body, "") &&
+			check.isTerminating(s.Else, "") {
+			return true
+		}
+
+	case *ast.SwitchStmt:
+		return check.isTerminatingSwitch(s.Body, label)
+
+	case *ast.TypeSwitchStmt:
+		return check.isTerminatingSwitch(s.Body, label)
+
+	case *ast.SelectStmt:
+		for _, s := range s.Body.List {
+			cc := s.(*ast.CommClause)
+			if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+				return false
+			}
+
+		}
+		return true
+
+	case *ast.ForStmt:
+		if s.Cond == nil && !hasBreak(s.Body, label, true) {
+			return true
+		}
+
+	}
+
+	return false
+}
+
+func (check *checker) isTerminatingList(list []ast.Stmt, label string) bool {
+	n := len(list)
+	return n > 0 && check.isTerminating(list[n-1], label)
+}
+
+func (check *checker) isTerminatingSwitch(body *ast.BlockStmt, label string) bool {
+	hasDefault := false
+	for _, s := range body.List {
+		cc := s.(*ast.CaseClause)
+		if cc.List == nil {
+			hasDefault = true
+		}
+		if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+			return false
+		}
+	}
+	return hasDefault
+}
+
+// hasBreak reports if s is or contains a break statement
+// referring to the label-ed statement or implicit-ly the
+// closest outer breakable statement.
+func hasBreak(s ast.Stmt, label string, implicit bool) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.ExprStmt,
+		*ast.SendStmt, *ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt,
+		*ast.DeferStmt, *ast.ReturnStmt:
+		// no chance
+
+	case *ast.LabeledStmt:
+		return hasBreak(s.Stmt, label, implicit)
+
+	case *ast.BranchStmt:
+		if s.Tok == token.BREAK {
+			if s.Label == nil {
+				return implicit
+			}
+			if s.Label.Name == label {
+				return true
+			}
+		}
+
+	case *ast.BlockStmt:
+		return hasBreakList(s.List, label, implicit)
+
+	case *ast.IfStmt:
+		if hasBreak(s.Body, label, implicit) ||
+			s.Else != nil && hasBreak(s.Else, label, implicit) {
+			return true
+		}
+
+	case *ast.CaseClause:
+		return hasBreakList(s.Body, label, implicit)
+
+	case *ast.SwitchStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.TypeSwitchStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.CommClause:
+		return hasBreakList(s.Body, label, implicit)
+
+	case *ast.SelectStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.ForStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.RangeStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func hasBreakList(list []ast.Stmt, label string, implicit bool) bool {
+	for _, s := range list {
+		if hasBreak(s, label, implicit) {
+			return true
+		}
+	}
+	return false
+}