cmd/compile: support arbitrarily deep embedded fields

Fixes #13337.

Change-Id: Ie74d00390111796619150287d3f7a147750ab456
Reviewed-on: https://go-review.googlesource.com/19932
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/go.go

@@ -192,10 +192,6 @@ type Sig struct {
 	offset int32
 }
 
-type Dlist struct {
-	field *Type
-}
-
 // argument passing to/from
 // smagic and umagic
 type Magic struct {
@@ -240,8 +236,6 @@ var sizeof_Array int // runtime sizeof(Array)
 // } String;
 var sizeof_String int // runtime sizeof(String)
 
-var dotlist [10]Dlist // size is max depth of embeddeds
-
 // lexlineno is the line number _after_ the most recently read rune.
 // In particular, it's advanced (or rewound) as newlines are read (or unread).
 var lexlineno int32

src/cmd/compile/internal/gc/subr.go

@@ -1564,14 +1564,22 @@ func Setmaxarg(t *Type, extra int32) {
 	}
 }
 
-// unicode-aware case-insensitive strcmp
+// Code to resolve elided DOTs in embedded types.
 
-// code to resolve elided DOTs
-// in embedded types
+// A Dlist stores a pointer to a TFIELD Type embedded within
+// a TSTRUCT or TINTER Type.
+type Dlist struct {
+	field *Type
+}
 
-// search depth 0 --
-// return count of fields+methods
-// found with a given name
+// dotlist is used by adddot1 to record the path of embedded fields
+// used to access a target field or method.
+// Must be non-nil so that dotpath returns a non-nil slice even if d is zero.
+var dotlist = make([]Dlist, 10)
+
+// lookdot0 returns the number of fields or methods named s associated
+// with Type t. If exactly one exists, it will be returned in *save
+// (if save is not nil).
 func lookdot0(s *Sym, t *Type, save **Type, ignorecase int) int {
 	u := t
 	if Isptr[u.Etype] {
@@ -1605,26 +1613,30 @@ func lookdot0(s *Sym, t *Type, save **Type, ignorecase int) int {
 	return c
 }
 
-// search depth d for field/method s --
-// return count of fields+methods
-// found at search depth.
-// answer is in dotlist array and
-// count of number of ways is returned.
-func adddot1(s *Sym, t *Type, d int, save **Type, ignorecase int) int {
+// adddot1 returns the number of fields or methods named s at depth d in Type t.
+// If exactly one exists, it will be returned in *save (if save is not nil),
+// and dotlist will contain the path of embedded fields traversed to find it,
+// in reverse order. If none exist, more will indicate whether t contains any
+// embedded fields at depth d, so callers can decide whether to retry at
+// a greater depth.
+func adddot1(s *Sym, t *Type, d int, save **Type, ignorecase int) (c int, more bool) {
 	if t.Trecur != 0 {
-		return 0
+		return
 	}
 	t.Trecur = 1
 
-	var c int
 	var u *Type
-	var a int
-	if d == 0 {
+	d--
+	if d < 0 {
+		// We've reached our target depth. If t has any fields/methods
+		// named s, then we're done. Otherwise, we still need to check
+		// below for embedded fields.
 		c = lookdot0(s, t, save, ignorecase)
-		goto out
+		if c != 0 {
+			goto out
+		}
 	}
 
-	c = 0
 	u = t
 	if Isptr[u.Etype] {
 		u = u.Type
@@ -1633,24 +1645,53 @@ func adddot1(s *Sym, t *Type, d int, save **Type, ignorecase int) int {
 		goto out
 	}
 
-	d--
 	for f := u.Type; f != nil; f = f.Down {
-		if f.Embedded == 0 {
+		if f.Embedded == 0 || f.Sym == nil {
 			continue
 		}
-		if f.Sym == nil {
-			continue
+		if d < 0 {
+			// Found an embedded field at target depth.
+			more = true
+			goto out
 		}
-		a = adddot1(s, f.Type, d, save, ignorecase)
+		a, more1 := adddot1(s, f.Type, d, save, ignorecase)
 		if a != 0 && c == 0 {
 			dotlist[d].field = f
 		}
 		c += a
+		if more1 {
+			more = true
+		}
 	}
 
 out:
 	t.Trecur = 0
-	return c
+	return c, more
+}
+
+// dotpath computes the unique shortest explicit selector path to fully qualify
+// a selection expression x.f, where x is of type t and f is the symbol s.
+// If no such path exists, dotpath returns nil.
+// If there are multiple shortest paths to the same depth, ambig is true.
+func dotpath(s *Sym, t *Type, save **Type, ignorecase int) (path []Dlist, ambig bool) {
+	// The embedding of types within structs imposes a tree structure onto
+	// types: structs parent the types they embed, and types parent their
+	// fields or methods. Our goal here is to find the shortest path to
+	// a field or method named s in the subtree rooted at t. To accomplish
+	// that, we iteratively perform depth-first searches of increasing depth
+	// until we either find the named field/method or exhaust the tree.
+	for d := 0; ; d++ {
+		if d > len(dotlist) {
+			dotlist = append(dotlist, Dlist{})
+		}
+		if c, more := adddot1(s, t, d, save, ignorecase); c == 1 {
+			return dotlist[:d], false
+		} else if c > 1 {
+			return nil, true
+		} else if !more {
+			return nil, false
+		}
+	}
 }
 
 // in T.field
@@ -1677,24 +1718,16 @@ func adddot(n *Node) *Node {
 		return n
 	}
 
-	var c int
-	for d := 0; d < len(dotlist); d++ {
-		c = adddot1(s, t, d, nil, 0)
-		if c > 0 {
-			if c > 1 {
-				Yyerror("ambiguous selector %v", n)
-				n.Left = nil
-				return n
-			}
-
-			// rebuild elided dots
-			for c := d - 1; c >= 0; c-- {
-				n.Left = Nod(ODOT, n.Left, newname(dotlist[c].field.Sym))
-				n.Left.Implicit = true
-			}
-
-			return n
+	switch path, ambig := dotpath(s, t, nil, 0); {
+	case path != nil:
+		// rebuild elided dots
+		for c := len(path) - 1; c >= 0; c-- {
+			n.Left = Nod(ODOT, n.Left, newname(path[c].field.Sym))
+			n.Left.Implicit = true
 		}
+	case ambig:
+		Yyerror("ambiguous selector %v", n)
+		n.Left = nil
 	}
 
 	return n
@@ -1758,16 +1791,13 @@ func expand0(t *Type, followptr bool) {
 	}
 }
 
-func expand1(t *Type, d int, followptr bool) {
+func expand1(t *Type, top, followptr bool) {
 	if t.Trecur != 0 {
 		return
 	}
-	if d == 0 {
-		return
-	}
 	t.Trecur = 1
 
-	if d != len(dotlist)-1 {
+	if !top {
 		expand0(t, followptr)
 	}
 
@@ -1788,7 +1818,7 @@ func expand1(t *Type, d int, followptr bool) {
 		if f.Sym == nil {
 			continue
 		}
-		expand1(f.Type, d-1, followptr)
+		expand1(f.Type, false, followptr)
 	}
 
 out:
@@ -1810,27 +1840,18 @@ func expandmeth(t *Type) {
 	// generate all reachable methods
 	slist = nil
 
-	expand1(t, len(dotlist)-1, false)
+	expand1(t, true, false)
 
 	// check each method to be uniquely reachable
-	var c int
-	var d int
 	for sl := slist; sl != nil; sl = sl.link {
 		sl.field.Sym.Flags &^= SymUniq
-		for d = 0; d < len(dotlist); d++ {
-			c = adddot1(sl.field.Sym, t, d, &f, 0)
-			if c == 0 {
-				continue
-			}
-			if c == 1 {
-				// addot1 may have dug out arbitrary fields, we only want methods.
-				if f.Type.Etype == TFUNC && f.Type.Thistuple > 0 {
-					sl.good = true
-					sl.field = f
-				}
-			}
-
-			break
+		if path, _ := dotpath(sl.field.Sym, t, &f, 0); path == nil {
+			continue
+		}
+		// dotpath may have dug out arbitrary fields, we only want methods.
+		if f.Type.Etype == TFUNC && f.Type.Thistuple > 0 {
+			sl.good = true
+			sl.field = f
 		}
 	}
 
@@ -1991,6 +2012,7 @@ func genwrapper(rcvr *Type, method *Type, newnam *Sym, iface int) {
 	if !instrumenting && Isptr[rcvr.Etype] && Isptr[methodrcvr.Etype] && method.Embedded != 0 && !isifacemethod(method.Type) {
 		// generate tail call: adjust pointer receiver and jump to embedded method.
 		dot = dot.Left // skip final .M
+		// TODO(mdempsky): Remove dependency on dotlist.
 		if !Isptr[dotlist[0].field.Type.Etype] {
 			dot = Nod(OADDR, dot, nil)
 		}
@@ -2058,33 +2080,27 @@ func ifacelookdot(s *Sym, t *Type, followptr *bool, ignorecase int) *Type {
 	}
 
 	var m *Type
-	var i int
-	var c int
-	for d := 0; d < len(dotlist); d++ {
-		c = adddot1(s, t, d, &m, ignorecase)
-		if c > 1 {
+	path, ambig := dotpath(s, t, &m, ignorecase)
+	if path == nil {
+		if ambig {
 			Yyerror("%v.%v is ambiguous", t, s)
-			return nil
 		}
+		return nil
+	}
 
-		if c == 1 {
-			for i = 0; i < d; i++ {
-				if Isptr[dotlist[i].field.Type.Etype] {
-					*followptr = true
-					break
-				}
-			}
-
-			if m.Type.Etype != TFUNC || m.Type.Thistuple == 0 {
-				Yyerror("%v.%v is a field, not a method", t, s)
-				return nil
-			}
-
-			return m
+	for _, d := range path {
+		if Isptr[d.field.Type.Etype] {
+			*followptr = true
+			break
 		}
 	}
 
-	return nil
+	if m.Type.Etype != TFUNC || m.Type.Thistuple == 0 {
+		Yyerror("%v.%v is a field, not a method", t, s)
+		return nil
+	}
+
+	return m
 }
 
 func implements(t *Type, iface *Type, m **Type, samename **Type, ptr *int) bool {

test/fixedbugs/issue13337.go

@@ -0,0 +1,30 @@
+// compile
+
+// Copyright 2016 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.
+
+// Issue 13337: The Go compiler limited how deeply embedded types
+// were searched for promoted fields and methods.
+
+package s
+
+type S0 struct{ f int }
+func (S0) m() {}
+
+type S1 struct{ S0 }
+type S2 struct{ S1 }
+type S3 struct{ S2 }
+type S4 struct{ S3 }
+type S5 struct{ S4 }
+type S6 struct{ S5 }
+type S7 struct{ S6 }
+type S8 struct{ S7 }
+type S9 struct{ S8 }
+type S10 struct{ S9 }
+type S11 struct{ S10 }
+type S12 struct{ S11 }
+type S13 struct{ S12 }
+
+var _ = S13{}.f
+var _ = S13.m