libgo: update to Go1.17rc2

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/341629

2 files changed, 38 insertions, 6 deletions

diff --git a/libgo/go/regexp/syntax/compile.go b/libgo/go/regexp/syntax/compile.go
index 7524d62..c9f9fa0 100644
--- a/libgo/go/regexp/syntax/compile.go
+++ b/libgo/go/regexp/syntax/compile.go
@@ -57,8 +57,9 @@ func (l1 patchList) append(p *Prog, l2 patchList) patchList {
 
 // A frag represents a compiled program fragment.
 type frag struct {
-	i   uint32    // index of first instruction
-	out patchList // where to record end instruction
+	i        uint32    // index of first instruction
+	out      patchList // where to record end instruction
+	nullable bool      // whether fragment can match empty string
 }
 
 type compiler struct {
@@ -159,7 +160,7 @@ func (c *compiler) compile(re *Regexp) frag {
 
 func (c *compiler) inst(op InstOp) frag {
 	// TODO: impose length limit
-	f := frag{i: uint32(len(c.p.Inst))}
+	f := frag{i: uint32(len(c.p.Inst)), nullable: true}
 	c.p.Inst = append(c.p.Inst, Inst{Op: op})
 	return f
 }
@@ -194,7 +195,7 @@ func (c *compiler) cat(f1, f2 frag) frag {
 	// TODO: elide nop
 
 	f1.out.patch(c.p, f2.i)
-	return frag{f1.i, f2.out}
+	return frag{f1.i, f2.out, f1.nullable && f2.nullable}
 }
 
 func (c *compiler) alt(f1, f2 frag) frag {
@@ -211,6 +212,7 @@ func (c *compiler) alt(f1, f2 frag) frag {
 	i.Out = f1.i
 	i.Arg = f2.i
 	f.out = f1.out.append(c.p, f2.out)
+	f.nullable = f1.nullable || f2.nullable
 	return f
 }
 
@@ -228,7 +230,12 @@ func (c *compiler) quest(f1 frag, nongreedy bool) frag {
 	return f
 }
 
-func (c *compiler) star(f1 frag, nongreedy bool) frag {
+// loop returns the fragment for the main loop of a plus or star.
+// For plus, it can be used after changing the entry to f1.i.
+// For star, it can be used directly when f1 can't match an empty string.
+// (When f1 can match an empty string, f1* must be implemented as (f1+)?
+// to get the priority match order correct.)
+func (c *compiler) loop(f1 frag, nongreedy bool) frag {
 	f := c.inst(InstAlt)
 	i := &c.p.Inst[f.i]
 	if nongreedy {
@@ -242,8 +249,17 @@ func (c *compiler) star(f1 frag, nongreedy bool) frag {
 	return f
 }
 
+func (c *compiler) star(f1 frag, nongreedy bool) frag {
+	if f1.nullable {
+		// Use (f1+)? to get priority match order correct.
+		// See golang.org/issue/46123.
+		return c.quest(c.plus(f1, nongreedy), nongreedy)
+	}
+	return c.loop(f1, nongreedy)
+}
+
 func (c *compiler) plus(f1 frag, nongreedy bool) frag {
-	return frag{f1.i, c.star(f1, nongreedy).out}
+	return frag{f1.i, c.loop(f1, nongreedy).out, f1.nullable}
 }
 
 func (c *compiler) empty(op EmptyOp) frag {
@@ -255,6 +271,7 @@ func (c *compiler) empty(op EmptyOp) frag {
 
 func (c *compiler) rune(r []rune, flags Flags) frag {
 	f := c.inst(InstRune)
+	f.nullable = false
 	i := &c.p.Inst[f.i]
 	i.Rune = r
 	flags &= FoldCase // only relevant flag is FoldCase
diff --git a/libgo/go/regexp/syntax/prog_test.go b/libgo/go/regexp/syntax/prog_test.go
index 50bfa3d..5603aea 100644
--- a/libgo/go/regexp/syntax/prog_test.go
+++ b/libgo/go/regexp/syntax/prog_test.go
@@ -89,6 +89,21 @@ var compileTests = []struct {
   2	anynotnl -> 3
   3	match
 `},
+	{"(?:|a)+", `  0	fail
+  1	nop -> 4
+  2	rune1 "a" -> 4
+  3*	alt -> 1, 2
+  4	alt -> 3, 5
+  5	match
+`},
+	{"(?:|a)*", `  0	fail
+  1	nop -> 4
+  2	rune1 "a" -> 4
+  3	alt -> 1, 2
+  4	alt -> 3, 6
+  5*	alt -> 3, 6
+  6	match
+`},
 }
 
 func TestCompile(t *testing.T) {