[dev.typeparams] cmd/compile/internal/importer, types2: initial check-in of types2 and importer

This is a copy of the importer and types2 (unreviewed) prototype version
excluding the testdata directory containing tests (see below). Each file
is marked with the comment

// UNREVIEWED

on the first line. The plan is to check in this code wholesale (it runs and
passes all tests) and then review the code file-by-file via subsequent CLs
and remove the "// UNREVIEWED" comments as we review the files.

Since most tests are unchanged from the original go/types, the next CL will
commit those tests as they don't need to be reviewed again. (Eventually we
may want to factor them out and share them from a single place, e.g. the
test directory.)

The existing file fmtmap_test.go was updated.

Change-Id: I9bd0ad1a7e7188b501423483a44d18e623c0fe71
Reviewed-on: https://go-review.googlesource.com/c/go/+/263624
Trust: Robert Griesemer <gri@golang.org>
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 180 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/return.go b/src/cmd/compile/internal/types2/return.go
new file mode 100644
index 0000000000..88234b1723
--- /dev/null
+++ b/src/cmd/compile/internal/types2/return.go
@@ -0,0 +1,180 @@
+// UNREVIEWED
+// 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 types2
+
+import (
+	"cmd/compile/internal/syntax"
+)
+
+// 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 syntax.Stmt, label string) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.SendStmt,
+		*syntax.AssignStmt, *syntax.CallStmt:
+		// no chance
+
+	case *syntax.LabeledStmt:
+		return check.isTerminating(s.Stmt, s.Label.Value)
+
+	case *syntax.ExprStmt:
+		// calling the predeclared (possibly parenthesized) panic() function is terminating
+		if call, ok := unparen(s.X).(*syntax.CallExpr); ok && check.isPanic[call] {
+			return true
+		}
+
+	case *syntax.ReturnStmt:
+		return true
+
+	case *syntax.BranchStmt:
+		if s.Tok == syntax.Goto || s.Tok == syntax.Fallthrough {
+			return true
+		}
+
+	case *syntax.BlockStmt:
+		return check.isTerminatingList(s.List, "")
+
+	case *syntax.IfStmt:
+		if s.Else != nil &&
+			check.isTerminating(s.Then, "") &&
+			check.isTerminating(s.Else, "") {
+			return true
+		}
+
+	case *syntax.SwitchStmt:
+		return check.isTerminatingSwitch(s.Body, label)
+
+	case *syntax.SelectStmt:
+		for _, cc := range s.Body {
+			if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+				return false
+			}
+
+		}
+		return true
+
+	case *syntax.ForStmt:
+		if s.Cond == nil && !hasBreak(s.Body, label, true) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (check *Checker) isTerminatingList(list []syntax.Stmt, label string) bool {
+	// trailing empty statements are permitted - skip them
+	for i := len(list) - 1; i >= 0; i-- {
+		if _, ok := list[i].(*syntax.EmptyStmt); !ok {
+			return check.isTerminating(list[i], label)
+		}
+	}
+	return false // all statements are empty
+}
+
+func (check *Checker) isTerminatingSwitch(body []*syntax.CaseClause, label string) bool {
+	hasDefault := false
+	for _, cc := range body {
+		if cc.Cases == nil {
+			hasDefault = true
+		}
+		if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+			return false
+		}
+	}
+	return hasDefault
+}
+
+// TODO(gri) For nested breakable statements, the current implementation of hasBreak
+//	     will traverse the same subtree repeatedly, once for each label. Replace
+//           with a single-pass label/break matching phase.
+
+// 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 syntax.Stmt, label string, implicit bool) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.ExprStmt,
+		*syntax.SendStmt, *syntax.AssignStmt, *syntax.CallStmt,
+		*syntax.ReturnStmt:
+		// no chance
+
+	case *syntax.LabeledStmt:
+		return hasBreak(s.Stmt, label, implicit)
+
+	case *syntax.BranchStmt:
+		if s.Tok == syntax.Break {
+			if s.Label == nil {
+				return implicit
+			}
+			if s.Label.Value == label {
+				return true
+			}
+		}
+
+	case *syntax.BlockStmt:
+		return hasBreakList(s.List, label, implicit)
+
+	case *syntax.IfStmt:
+		if hasBreak(s.Then, label, implicit) ||
+			s.Else != nil && hasBreak(s.Else, label, implicit) {
+			return true
+		}
+
+	case *syntax.SwitchStmt:
+		if label != "" && hasBreakCaseList(s.Body, label, false) {
+			return true
+		}
+
+	case *syntax.SelectStmt:
+		if label != "" && hasBreakCommList(s.Body, label, false) {
+			return true
+		}
+
+	case *syntax.ForStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func hasBreakList(list []syntax.Stmt, label string, implicit bool) bool {
+	for _, s := range list {
+		if hasBreak(s, label, implicit) {
+			return true
+		}
+	}
+	return false
+}
+
+func hasBreakCaseList(list []*syntax.CaseClause, label string, implicit bool) bool {
+	for _, s := range list {
+		if hasBreakList(s.Body, label, implicit) {
+			return true
+		}
+	}
+	return false
+}
+
+func hasBreakCommList(list []*syntax.CommClause, label string, implicit bool) bool {
+	for _, s := range list {
+		if hasBreakList(s.Body, label, implicit) {
+			return true
+		}
+	}
+	return false
+}