cmd/compile: minor cleanup to import loading

Briefly document what the importfoo functions do.

Get rid of importsym's unused result parameter.

Get rid of the redundant calls to importsym(s, OTYPE)
after we've already called pkgtype(s).

Passes toolstash -cmp.

Change-Id: I4c057358144044f5356e4dec68907ec85f1fe806
Reviewed-on: https://go-review.googlesource.com/21498
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -290,7 +290,6 @@ func (p *importer) typ() *Type {
 
 		// parser.go:hidden_pkgtype
 		t = pkgtype(tsym)
-		importsym(tsym, OTYPE)
 		p.typList = append(p.typList, t)
 
 		// read underlying type

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

@@ -445,10 +445,8 @@ func dumpexport() {
 	}
 }
 
-// import
-
-// return the sym for ss, which should match lexical
-func importsym(s *Sym, op Op) *Sym {
+// importsym declares symbol s as an imported object representable by op.
+func importsym(s *Sym, op Op) {
 	if s.Def != nil && s.Def.Op != op {
 		pkgstr := fmt.Sprintf("during import %q", importpkg.Path)
 		redeclare(s, pkgstr)
@@ -462,11 +460,10 @@ func importsym(s *Sym, op Op) *Sym {
 			s.Flags |= SymPackage // package scope
 		}
 	}
-
-	return s
 }
 
-// return the type pkg.name, forward declaring if needed
+// pkgtype returns the named type declared by symbol s.
+// If no such type has been declared yet, a forward declaration is returned.
 func pkgtype(s *Sym) *Type {
 	importsym(s, OTYPE)
 	if s.Def == nil || s.Def.Op != OTYPE {
@@ -506,6 +503,7 @@ func importimport(s *Sym, path string) {
 	}
 }
 
+// importconst declares symbol s as an imported constant with type t and value n.
 func importconst(s *Sym, t *Type, n *Node) {
 	importsym(s, OLITERAL)
 	n = convlit(n, t)
@@ -533,6 +531,7 @@ func importconst(s *Sym, t *Type, n *Node) {
 	}
 }
 
+// importvar declares symbol s as an imported variable with type t.
 func importvar(s *Sym, t *Type) {
 	importsym(s, ONAME)
 	if s.Def != nil && s.Def.Op == ONAME {

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

@@ -2931,12 +2931,7 @@ func (p *parser) hidden_pkgtype() *Type {
 		defer p.trace("hidden_pkgtype")()
 	}
 
-	s1 := p.hidden_pkg_importsym()
-
-	ss := pkgtype(s1)
-	importsym(s1, OTYPE)
-
-	return ss
+	return pkgtype(p.hidden_pkg_importsym())
 }
 
 // ----------------------------------------------------------------------------