[dev.regabi] cmd/compile: use ir.Ident for imported identifiers

This CL substantially reworks how imported declarations are handled,
and fixes a number of issues with dot imports. In particular:

1. It eliminates the stub ir.Name declarations that are created
upfront during import-declaration processing, allowing this to be
deferred to when the declarations are actually needed. (Eventually,
this can be deferred even further so we never have to create ir.Names
w/ ONONAME, but this CL is already invasive/subtle enough.)

2. During noding, we now use ir.Idents to represent uses of imported
declarations, including of dot-imported declarations.

3. Unused dot imports are now reported after type checking, so that we
can correctly distinguish whether composite literal keys are a simple
identifier (struct literals) or expressions (array/slice/map literals)
and whether it might be a use of a dot-imported declaration.

4. It changes the "redeclared" error messages to report the previous
position information in the same style as other compiler error
messages that reference other source lines.

Passes buildall w/ toolstash -cmp.

Fixes #6428.
Fixes #43164.
Fixes #43167.
Updates #42990.

Change-Id: I40a0a780ec40daf5700fbc3cfeeb7300e1055981
Reviewed-on: https://go-review.googlesource.com/c/go/+/277713
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

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

@@ -28,12 +28,9 @@ func testdclstack() {
 // redeclare emits a diagnostic about symbol s being redeclared at pos.
 func redeclare(pos src.XPos, s *types.Sym, where string) {
 	if !s.Lastlineno.IsKnown() {
-		pkg := s.Origpkg
-		if pkg == nil {
-			pkg = s.Pkg
-		}
+		pkgName := dotImportRefs[s.Def.(*ir.Ident)]
 		base.ErrorfAt(pos, "%v redeclared %s\n"+
-			"\tprevious declaration during import %q", s, where, pkg.Path)
+			"\t%v: previous declaration during import %q", s, where, base.FmtPos(pkgName.Pos()), pkgName.Pkg.Path)
 	} else {
 		prevPos := s.Lastlineno
 
@@ -46,7 +43,7 @@ func redeclare(pos src.XPos, s *types.Sym, where string) {
 		}
 
 		base.ErrorfAt(pos, "%v redeclared %s\n"+
-			"\tprevious declaration at %v", s, where, base.FmtPos(prevPos))
+			"\t%v: previous declaration", s, where, base.FmtPos(prevPos))
 	}
 }
 
@@ -210,6 +207,10 @@ func symfield(s *types.Sym, typ *types.Type) *ir.Field {
 // Automatically creates a new closure variable if the referenced symbol was
 // declared in a different (containing) function.
 func oldname(s *types.Sym) ir.Node {
+	if s.Pkg != types.LocalPkg {
+		return ir.NewIdent(base.Pos, s)
+	}
+
 	n := ir.AsNode(s.Def)
 	if n == nil {
 		// Maybe a top-level declaration will come along later to

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

@@ -165,17 +165,9 @@ func iimport(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintType)
 			s := pkg.Lookup(p.stringAt(ird.uint64()))
 			off := ird.uint64()
 
-			if _, ok := declImporter[s]; ok {
-				continue
+			if _, ok := declImporter[s]; !ok {
+				declImporter[s] = iimporterAndOffset{p, off}
 			}
-			declImporter[s] = iimporterAndOffset{p, off}
-
-			// Create stub declaration. If used, this will
-			// be overwritten by expandDecl.
-			if s.Def != nil {
-				base.Fatalf("unexpected definition for %v: %v", s, ir.AsNode(s.Def))
-			}
-			s.Def = ir.NewDeclNameAt(src.NoXPos, s)
 		}
 	}
 
@@ -187,10 +179,9 @@ func iimport(pkg *types.Pkg, in *bio.Reader) (fingerprint goobj.FingerprintType)
 			s := pkg.Lookup(p.stringAt(ird.uint64()))
 			off := ird.uint64()
 
-			if _, ok := inlineImporter[s]; ok {
-				continue
+			if _, ok := inlineImporter[s]; !ok {
+				inlineImporter[s] = iimporterAndOffset{p, off}
 			}
-			inlineImporter[s] = iimporterAndOffset{p, off}
 		}
 	}
 
@@ -442,10 +433,16 @@ func (r *importReader) ident() *types.Sym {
 	return pkg.Lookup(name)
 }
 
-func (r *importReader) qualifiedIdent() *types.Sym {
+func (r *importReader) qualifiedIdent() *ir.Name {
 	name := r.string()
 	pkg := r.pkg()
-	return pkg.Lookup(name)
+	sym := pkg.Lookup(name)
+	n := sym.PkgDef()
+	if n == nil {
+		n = ir.NewDeclNameAt(src.NoXPos, sym)
+		sym.SetPkgDef(n)
+	}
+	return n.(*ir.Name)
 }
 
 func (r *importReader) pos() src.XPos {
@@ -501,9 +498,9 @@ func (r *importReader) typ1() *types.Type {
 		// support inlining functions with local defined
 		// types. Therefore, this must be a package-scope
 		// type.
-		n := ir.AsNode(r.qualifiedIdent().PkgDef())
+		n := r.qualifiedIdent()
 		if n.Op() == ir.ONONAME {
-			expandDecl(n.(*ir.Name))
+			expandDecl(n)
 		}
 		if n.Op() != ir.OTYPE {
 			base.Fatalf("expected OTYPE, got %v: %v, %v", n.Op(), n.Sym(), n)
@@ -821,10 +818,10 @@ func (r *importReader) node() ir.Node {
 		return n
 
 	case ir.ONONAME:
-		return mkname(r.qualifiedIdent())
+		return r.qualifiedIdent()
 
 	case ir.ONAME:
-		return mkname(r.ident())
+		return r.ident().Def.(*ir.Name)
 
 	// case OPACK, ONONAME:
 	// 	unreachable - should have been resolved by typechecking

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

@@ -44,8 +44,8 @@ func fninit(n []ir.Node) {
 
 	// Find imported packages with init tasks.
 	for _, pkg := range sourceOrderImports {
-		n := resolve(ir.AsNode(pkg.Lookup(".inittask").Def))
-		if n == nil {
+		n := resolve(oldname(pkg.Lookup(".inittask")))
+		if n.Op() == ir.ONONAME {
 			continue
 		}
 		if n.Op() != ir.ONAME || n.Class() != ir.PEXTERN {

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

@@ -293,8 +293,10 @@ func Main(archInit func(*Arch)) {
 		}
 	}
 
-	// Phase 3.14: With all user code type-checked, it's now safe to verify map keys.
+	// Phase 3.14: With all user code type-checked, it's now safe to verify map keys
+	// and unused dot imports.
 	checkMapKeys()
+	checkDotImports()
 	base.ExitIfErrors()
 
 	timings.AddEvent(fcount, "funcs")
@@ -953,10 +955,7 @@ func clearImports() {
 		if IsAlias(s) {
 			// throw away top-level name left over
 			// from previous import . "x"
-			if name := n.Name(); name != nil && name.PkgName != nil && !name.PkgName.Used && base.SyntaxErrors() == 0 {
-				unused = append(unused, importedPkg{name.PkgName.Pos(), name.PkgName.Pkg.Path, ""})
-				name.PkgName.Used = true
-			}
+			// We'll report errors after type checking in checkDotImports.
 			s.Def = nil
 			continue
 		}

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

@@ -369,7 +369,7 @@ func (p *noder) importDecl(imp *syntax.ImportDecl) {
 
 	switch my.Name {
 	case ".":
-		importdot(ipkg, pack)
+		importDot(pack)
 		return
 	case "init":
 		base.ErrorfAt(pack.Pos(), "cannot import package as init - init must be a func")

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

@@ -100,13 +100,26 @@ func autolabel(prefix string) *types.Sym {
 	return lookupN(prefix, int(n))
 }
 
-// find all the exported symbols in package opkg
+// dotImports tracks all PkgNames that have been dot-imported.
+var dotImports []*ir.PkgName
+
+// dotImportRefs maps idents introduced by importDot back to the
+// ir.PkgName they were dot-imported through.
+var dotImportRefs map[*ir.Ident]*ir.PkgName
+
+// find all the exported symbols in package referenced by PkgName,
 // and make them available in the current package
-func importdot(opkg *types.Pkg, pack *ir.PkgName) {
-	n := 0
+func importDot(pack *ir.PkgName) {
+	if dotImportRefs == nil {
+		dotImportRefs = make(map[*ir.Ident]*ir.PkgName)
+	}
+
+	opkg := pack.Pkg
 	for _, s := range opkg.Syms {
 		if s.Def == nil {
-			continue
+			if _, ok := declImporter[s]; !ok {
+				continue
+			}
 		}
 		if !types.IsExported(s.Name) || strings.ContainsRune(s.Name, 0xb7) { // 0xb7 = center dot
 			continue
@@ -118,21 +131,26 @@ func importdot(opkg *types.Pkg, pack *ir.PkgName) {
 			continue
 		}
 
-		s1.Def = s.Def
-		s1.Block = s.Block
-		if ir.AsNode(s1.Def).Name() == nil {
-			ir.Dump("s1def", ir.AsNode(s1.Def))
-			base.Fatalf("missing Name")
-		}
-		ir.AsNode(s1.Def).Name().PkgName = pack
-		s1.Origpkg = opkg
-		n++
+		id := ir.NewIdent(src.NoXPos, s)
+		dotImportRefs[id] = pack
+		s1.Def = id
+		s1.Block = 1
 	}
 
-	if n == 0 {
-		// can't possibly be used - there were no symbols
-		base.ErrorfAt(pack.Pos(), "imported and not used: %q", opkg.Path)
+	dotImports = append(dotImports, pack)
+}
+
+// checkDotImports reports errors for any unused dot imports.
+func checkDotImports() {
+	for _, pack := range dotImports {
+		if !pack.Used {
+			base.ErrorfAt(pack.Pos(), "imported and not used: %q", pack.Pkg.Path)
+		}
 	}
+
+	// No longer needed; release memory.
+	dotImports = nil
+	dotImportRefs = nil
 }
 
 // nodAddr returns a node representing &n.

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

@@ -8,6 +8,7 @@ import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/types"
+	"cmd/internal/src"
 	"fmt"
 	"go/constant"
 	"go/token"
@@ -90,11 +91,24 @@ func resolve(n ir.Node) (res ir.Node) {
 		defer tracePrint("resolve", n)(&res)
 	}
 
-	// Stub ir.Name left for us by iimport.
-	if n, ok := n.(*ir.Name); ok {
-		if n.Sym().Pkg == types.LocalPkg {
-			base.Fatalf("unexpected Name: %+v", n)
+	if sym := n.Sym(); sym.Pkg != types.LocalPkg {
+		// We might have an ir.Ident from oldname or importDot.
+		if id, ok := n.(*ir.Ident); ok {
+			if pkgName := dotImportRefs[id]; pkgName != nil {
+				pkgName.Used = true
+			}
+
+			if sym.Def == nil {
+				if _, ok := declImporter[sym]; !ok {
+					return n // undeclared name
+				}
+				sym.Def = ir.NewDeclNameAt(src.NoXPos, sym)
+			}
+			n = ir.AsNode(sym.Def)
 		}
+
+		// Stub ir.Name left for us by iimport.
+		n := n.(*ir.Name)
 		if inimport {
 			base.Fatalf("recursive inimport")
 		}
@@ -2885,31 +2899,25 @@ func typecheckcomplit(n ir.Node) (res ir.Node) {
 				if l.Op() == ir.OKEY {
 					key := l.Left()
 
-					sk := ir.NewStructKeyExpr(l.Pos(), nil, l.Right())
-					ls[i] = sk
-					l = sk
+					// Sym might have resolved to name in other top-level
+					// package, because of import dot. Redirect to correct sym
+					// before we do the lookup.
+					s := key.Sym()
+					if id, ok := key.(*ir.Ident); ok && dotImportRefs[id] != nil {
+						s = lookup(s.Name)
+					}
 
 					// An OXDOT uses the Sym field to hold
 					// the field to the right of the dot,
 					// so s will be non-nil, but an OXDOT
 					// is never a valid struct literal key.
-					if key.Sym() == nil || key.Op() == ir.OXDOT || key.Sym().IsBlank() {
+					if s == nil || s.Pkg != types.LocalPkg || key.Op() == ir.OXDOT || s.IsBlank() {
 						base.Errorf("invalid field name %v in struct initializer", key)
-						sk.SetLeft(typecheck(sk.Left(), ctxExpr))
 						continue
 					}
 
-					// Sym might have resolved to name in other top-level
-					// package, because of import dot. Redirect to correct sym
-					// before we do the lookup.
-					s := key.Sym()
-					if s.Pkg != types.LocalPkg && types.IsExported(s.Name) {
-						s1 := lookup(s.Name)
-						if s1.Origpkg == s.Pkg {
-							s = s1
-						}
-					}
-					sk.SetSym(s)
+					l = ir.NewStructKeyExpr(l.Pos(), s, l.Right())
+					ls[i] = l
 				}
 
 				if l.Op() != ir.OSTRUCTKEY {

src/cmd/compile/internal/ir/name.go

@@ -16,8 +16,7 @@ import (
 // An Ident is an identifier, possibly qualified.
 type Ident struct {
 	miniExpr
-	sym  *types.Sym
-	Used bool
+	sym *types.Sym
 }
 
 func NewIdent(pos src.XPos, sym *types.Sym) *Ident {

src/cmd/compile/internal/types/sizeof_test.go

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Sym{}, 52, 88},
+		{Sym{}, 48, 80},
 		{Type{}, 56, 96},
 		{Map{}, 20, 40},
 		{Forward{}, 20, 32},

src/cmd/compile/internal/types/sym.go

@@ -38,8 +38,7 @@ type Sym struct {
 	Block      int32    // blocknumber to catch redeclaration
 	Lastlineno src.XPos // last declaration for diagnostic
 
-	flags   bitset8
-	Origpkg *Pkg // original package for . import
+	flags bitset8
 }
 
 const (

test/fixedbugs/bug462.go

@@ -13,7 +13,7 @@ type T struct {
 }
 
 func main() {
-	_ = T {
-		os.File: 1, // ERROR "unknown T? ?field"
+	_ = T{
+		os.File: 1, // ERROR "invalid field name os.File|unknown field"
 	}
 }

test/fixedbugs/issue20415.go

@@ -11,7 +11,7 @@ package p
 // 1
 var f byte
 
-var f interface{} // ERROR "previous declaration at issue20415.go:12"
+var f interface{} // ERROR "issue20415.go:12: previous declaration"
 
 func _(f int) {
 }
@@ -22,7 +22,7 @@ var g byte
 func _(g int) {
 }
 
-var g interface{} // ERROR "previous declaration at issue20415.go:20"
+var g interface{} // ERROR "issue20415.go:20: previous declaration"
 
 // 3
 func _(h int) {
@@ -30,4 +30,4 @@ func _(h int) {
 
 var h byte
 
-var h interface{} // ERROR "previous declaration at issue20415.go:31"
+var h interface{} // ERROR "issue20415.go:31: previous declaration"

test/fixedbugs/issue43164.dir/a.go

@@ -0,0 +1,13 @@
+// Copyright 2020 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.
+
+package p
+
+import . "strings"
+
+var _ = Index // use strings
+
+type t struct{ Index int }
+
+var _ = t{Index: 0}

test/fixedbugs/issue43164.dir/b.go

@@ -0,0 +1,11 @@
+// Copyright 2020 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.
+
+package p
+
+import . "bytes"
+
+var _ = Index // use bytes
+
+var _ = t{Index: 0}

test/fixedbugs/issue43164.go

@@ -0,0 +1,7 @@
+// compiledir
+
+// Copyright 2020 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.
+
+package ignored

test/fixedbugs/issue43167.go

@@ -0,0 +1,13 @@
+// errorcheck
+
+// Copyright 2020 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.
+
+package p
+
+import . "bytes"
+
+var _ Buffer // use package bytes
+
+var Index byte // ERROR "Index redeclared.*\n\tLINE-4: previous declaration during import .bytes.|already declared|redefinition"

test/fixedbugs/issue6428.go

@@ -0,0 +1,15 @@
+// errorcheck
+
+// Copyright 2020 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.
+
+package p
+
+import . "testing" // ERROR "imported and not used"
+
+type S struct {
+	T int
+}
+
+var _ = S{T: 0}