[dev.typeparams] cmd/compile/internal/types2: remove MethodSet code - not used by types2

We can always re-introduce it if we decide to make use of it.

Change-Id: Ia939fdae978568edc58e21d1af732c6137744aab
Reviewed-on: https://go-review.googlesource.com/c/go/+/285678
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

5 files changed, 21 insertions, 365 deletions

diff --git a/src/cmd/compile/internal/importer/gcimporter_test.go b/src/cmd/compile/internal/importer/gcimporter_test.go
index a275524484..7fb8fed59c 100644
--- a/src/cmd/compile/internal/importer/gcimporter_test.go
+++ b/src/cmd/compile/internal/importer/gcimporter_test.go
@@ -384,9 +384,8 @@ func TestCorrectMethodPackage(t *testing.T) {
 	}
 
 	mutex := imports["sync"].Scope().Lookup("Mutex").(*types2.TypeName).Type()
-	mset := types2.NewMethodSet(types2.NewPointer(mutex)) // methods of *sync.Mutex
-	sel := mset.Lookup(nil, "Lock")
-	lock := sel.Obj().(*types2.Func)
+	obj, _, _ := types2.LookupFieldOrMethod(types2.NewPointer(mutex), false, nil, "Lock")
+	lock := obj.(*types2.Func)
 	if got, want := lock.Pkg().Path(), "sync"; got != want {
 		t.Errorf("got package path %q; want %q", got, want)
 	}
diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 5a7ae221e6..72a33b50b1 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -685,51 +685,6 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 			// addressability, should we report the type &(x.typ) instead?
 			check.recordSelection(e, MethodVal, x.typ, obj, index, indirect)
 
-			// TODO(gri) The verification pass below is disabled for now because
-			//           method sets don't match method lookup in some cases.
-			//           For instance, if we made a copy above when creating a
-			//           custom method for a parameterized received type, the
-			//           method set method doesn't match (no copy there). There
-			///          may be other situations.
-			disabled := true
-			if !disabled && debug {
-				// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
-				// TODO(gri) This only works because we call LookupFieldOrMethod
-				// _before_ calling NewMethodSet: LookupFieldOrMethod completes
-				// any incomplete interfaces so they are available to NewMethodSet
-				// (which assumes that interfaces have been completed already).
-				typ := x.typ
-				if x.mode == variable {
-					// If typ is not an (unnamed) pointer or an interface,
-					// use *typ instead, because the method set of *typ
-					// includes the methods of typ.
-					// Variables are addressable, so we can always take their
-					// address.
-					if _, ok := typ.(*Pointer); !ok && !IsInterface(typ) {
-						typ = &Pointer{base: typ}
-					}
-				}
-				// If we created a synthetic pointer type above, we will throw
-				// away the method set computed here after use.
-				// TODO(gri) Method set computation should probably always compute
-				// both, the value and the pointer receiver method set and represent
-				// them in a single structure.
-				// TODO(gri) Consider also using a method set cache for the lifetime
-				// of checker once we rely on MethodSet lookup instead of individual
-				// lookup.
-				mset := NewMethodSet(typ)
-				if m := mset.Lookup(check.pkg, sel); m == nil || m.obj != obj {
-					check.dump("%v: (%s).%v -> %s", posFor(e), typ, obj.name, m)
-					check.dump("%s\n", mset)
-					// Caution: MethodSets are supposed to be used externally
-					// only (after all interface types were completed). It's
-					// now possible that we get here incorrectly. Not urgent
-					// to fix since we only run this code in debug mode.
-					// TODO(gri) fix this eventually.
-					panic("method sets and lookup don't agree")
-				}
-			}
-
 			x.mode = value
 
 			// remove receiver
diff --git a/src/cmd/compile/internal/types2/example_test.go b/src/cmd/compile/internal/types2/example_test.go
index dcdeaca0c0..ffd54fe459 100644
--- a/src/cmd/compile/internal/types2/example_test.go
+++ b/src/cmd/compile/internal/types2/example_test.go
@@ -107,61 +107,6 @@ func Unused() { {}; {{ var x int; _ = x }} } // make sure empty block scopes get
 	// }
 }
 
-// ExampleMethodSet prints the method sets of various types.
-func ExampleMethodSet() {
-	// Parse a single source file.
-	const input = `
-package temperature
-import "fmt"
-type Celsius float64
-func (c Celsius) String() string  { return fmt.Sprintf("%g°C", c) }
-func (c *Celsius) SetF(f float64) { *c = Celsius(f - 32 / 9 * 5) }
-
-type S struct { I; m int }
-type I interface { m() byte }
-`
-	f, err := parseSrc("celsius.go", input)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	// Type-check a package consisting of this file.
-	// Type information for the imported packages
-	// comes from $GOROOT/pkg/$GOOS_$GOOARCH/fmt.a.
-	conf := types2.Config{Importer: defaultImporter()}
-	pkg, err := conf.Check("temperature", []*syntax.File{f}, nil)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	// Print the method sets of Celsius and *Celsius.
-	celsius := pkg.Scope().Lookup("Celsius").Type()
-	for _, t := range []types2.Type{celsius, types2.NewPointer(celsius)} {
-		fmt.Printf("Method set of %s:\n", t)
-		mset := types2.NewMethodSet(t)
-		for i := 0; i < mset.Len(); i++ {
-			fmt.Println(mset.At(i))
-		}
-		fmt.Println()
-	}
-
-	// Print the method set of S.
-	styp := pkg.Scope().Lookup("S").Type()
-	fmt.Printf("Method set of %s:\n", styp)
-	fmt.Println(types2.NewMethodSet(styp))
-
-	// Output:
-	// Method set of temperature.Celsius:
-	// method (temperature.Celsius) String() string
-	//
-	// Method set of *temperature.Celsius:
-	// method (*temperature.Celsius) SetF(f float64)
-	// method (*temperature.Celsius) String() string
-	//
-	// Method set of temperature.S:
-	// MethodSet {}
-}
-
 // ExampleInfo prints various facts recorded by the type checker in a
 // types2.Info struct: definitions of and references to each named object,
 // and the type, value, and mode of every expression in the package.
diff --git a/src/cmd/compile/internal/types2/lookup.go b/src/cmd/compile/internal/types2/lookup.go
index e1e7b5814d..5dfb8bfee7 100644
--- a/src/cmd/compile/internal/types2/lookup.go
+++ b/src/cmd/compile/internal/types2/lookup.go
@@ -491,3 +491,22 @@ func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
 	}
 	return -1, nil
 }
+
+// ptrRecv reports whether the receiver is of the form *T.
+func ptrRecv(f *Func) bool {
+	// If a method's receiver type is set, use that as the source of truth for the receiver.
+	// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
+	// signature. We may reach here before the signature is fully set up: we must explicitly
+	// check if the receiver is set (we cannot just look for non-nil f.typ).
+	if sig, _ := f.typ.(*Signature); sig != nil && sig.recv != nil {
+		_, isPtr := deref(sig.recv.typ)
+		return isPtr
+	}
+
+	// If a method's type is not set it may be a method/function that is:
+	// 1) client-supplied (via NewFunc with no signature), or
+	// 2) internally created but not yet type-checked.
+	// For case 1) we can't do anything; the client must know what they are doing.
+	// For case 2) we can use the information gathered by the resolver.
+	return f.hasPtrRecv
+}
diff --git a/src/cmd/compile/internal/types2/methodset.go b/src/cmd/compile/internal/types2/methodset.go
deleted file mode 100644
index eb8f1221cc..0000000000
--- a/src/cmd/compile/internal/types2/methodset.go
+++ /dev/null
@@ -1,262 +0,0 @@
-// 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 method sets.
-
-package types2
-
-import (
-	"bytes"
-	"fmt"
-	"sort"
-)
-
-// A MethodSet is an ordered set of concrete or abstract (interface) methods;
-// a method is a MethodVal selection, and they are ordered by ascending m.Obj().Id().
-// The zero value for a MethodSet is a ready-to-use empty method set.
-type MethodSet struct {
-	list []*Selection
-}
-
-func (s *MethodSet) String() string {
-	if s.Len() == 0 {
-		return "MethodSet {}"
-	}
-
-	// Would like to use strings.Builder but it's not available in Go 1.4.
-	var buf bytes.Buffer
-	fmt.Fprintln(&buf, "MethodSet {")
-	for _, f := range s.list {
-		fmt.Fprintf(&buf, "\t%s\n", f)
-	}
-	fmt.Fprintln(&buf, "}")
-	return buf.String()
-}
-
-// Len returns the number of methods in s.
-func (s *MethodSet) Len() int { return len(s.list) }
-
-// At returns the i'th method in s for 0 <= i < s.Len().
-func (s *MethodSet) At(i int) *Selection { return s.list[i] }
-
-// Lookup returns the method with matching package and name, or nil if not found.
-func (s *MethodSet) Lookup(pkg *Package, name string) *Selection {
-	if s.Len() == 0 {
-		return nil
-	}
-
-	key := Id(pkg, name)
-	i := sort.Search(len(s.list), func(i int) bool {
-		m := s.list[i]
-		return m.obj.Id() >= key
-	})
-	if i < len(s.list) {
-		m := s.list[i]
-		if m.obj.Id() == key {
-			return m
-		}
-	}
-	return nil
-}
-
-// Shared empty method set.
-var emptyMethodSet MethodSet
-
-// Note: NewMethodSet is intended for external use only as it
-//       requires interfaces to be complete. If may be used
-//       internally if LookupFieldOrMethod completed the same
-//       interfaces beforehand.
-
-// NewMethodSet returns the method set for the given type T.
-// It always returns a non-nil method set, even if it is empty.
-func NewMethodSet(T Type) *MethodSet {
-	// WARNING: The code in this function is extremely subtle - do not modify casually!
-	//          This function and lookupFieldOrMethod should be kept in sync.
-
-	// method set up to the current depth, allocated lazily
-	var base methodSet
-
-	typ, isPtr := deref(T)
-
-	// *typ where typ is an interface has no methods.
-	if isPtr && IsInterface(typ) {
-		return &emptyMethodSet
-	}
-
-	// Start with typ as single entry at shallowest depth.
-	current := []embeddedType{{typ, nil, isPtr, false}}
-
-	// Named types that we have seen already, allocated lazily.
-	// Used to avoid endless searches in case of recursive types.
-	// Since only Named types can be used for recursive types, we
-	// only need to track those.
-	// (If we ever allow type aliases to construct recursive types,
-	// we must use type identity rather than pointer equality for
-	// the map key comparison, as we do in consolidateMultiples.)
-	var seen map[*Named]bool
-
-	// collect methods at current depth
-	for len(current) > 0 {
-		var next []embeddedType // embedded types found at current depth
-
-		// field and method sets at current depth, indexed by names (Id's), and allocated lazily
-		var fset map[string]bool // we only care about the field names
-		var mset methodSet
-
-		for _, e := range current {
-			typ := e.typ
-
-			// If we have a named type, we may have associated methods.
-			// Look for those first.
-			if named := typ.Named(); named != nil {
-				if seen[named] {
-					// We have seen this type before, at a more shallow depth
-					// (note that multiples of this type at the current depth
-					// were consolidated before). The type at that depth shadows
-					// this same type at the current depth, so we can ignore
-					// this one.
-					continue
-				}
-				if seen == nil {
-					seen = make(map[*Named]bool)
-				}
-				seen[named] = true
-
-				mset = mset.add(named.methods, e.index, e.indirect, e.multiples)
-
-				// continue with underlying type
-				typ = named.underlying
-			}
-
-			switch t := typ.(type) {
-			case *Struct:
-				for i, f := range t.fields {
-					if fset == nil {
-						fset = make(map[string]bool)
-					}
-					fset[f.Id()] = true
-
-					// Embedded fields are always of the form T or *T where
-					// T is a type name. If typ appeared multiple times at
-					// this depth, f.Type appears multiple times at the next
-					// depth.
-					if f.embedded {
-						typ, isPtr := deref(f.typ)
-						// TODO(gri) optimization: ignore types that can't
-						// have fields or methods (only Named, Struct, and
-						// Interface types need to be considered).
-						next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
-					}
-				}
-
-			case *Interface:
-				mset = mset.add(t.allMethods, e.index, true, e.multiples)
-			}
-		}
-
-		// Add methods and collisions at this depth to base if no entries with matching
-		// names exist already.
-		for k, m := range mset {
-			if _, found := base[k]; !found {
-				// Fields collide with methods of the same name at this depth.
-				if fset[k] {
-					m = nil // collision
-				}
-				if base == nil {
-					base = make(methodSet)
-				}
-				base[k] = m
-			}
-		}
-
-		// Add all (remaining) fields at this depth as collisions (since they will
-		// hide any method further down) if no entries with matching names exist already.
-		for k := range fset {
-			if _, found := base[k]; !found {
-				if base == nil {
-					base = make(methodSet)
-				}
-				base[k] = nil // collision
-			}
-		}
-
-		// It's ok to call consolidateMultiples with a nil *Checker because
-		// MethodSets are not used internally (outside debug mode). When used
-		// externally, interfaces are expected to be completed and then we do
-		// not need a *Checker to complete them when (indirectly) calling
-		// Checker.identical via consolidateMultiples.
-		current = (*Checker)(nil).consolidateMultiples(next)
-	}
-
-	if len(base) == 0 {
-		return &emptyMethodSet
-	}
-
-	// collect methods
-	var list []*Selection
-	for _, m := range base {
-		if m != nil {
-			m.recv = T
-			list = append(list, m)
-		}
-	}
-	// sort by unique name
-	sort.Slice(list, func(i, j int) bool {
-		return list[i].obj.Id() < list[j].obj.Id()
-	})
-	return &MethodSet{list}
-}
-
-// A methodSet is a set of methods and name collisions.
-// A collision indicates that multiple methods with the
-// same unique id, or a field with that id appeared.
-type methodSet map[string]*Selection // a nil entry indicates a name collision
-
-// Add adds all functions in list to the method set s.
-// If multiples is set, every function in list appears multiple times
-// and is treated as a collision.
-func (s methodSet) add(list []*Func, index []int, indirect bool, multiples bool) methodSet {
-	if len(list) == 0 {
-		return s
-	}
-	if s == nil {
-		s = make(methodSet)
-	}
-	for i, f := range list {
-		key := f.Id()
-		// if f is not in the set, add it
-		if !multiples {
-			// TODO(gri) A found method may not be added because it's not in the method set
-			// (!indirect && ptrRecv(f)). A 2nd method on the same level may be in the method
-			// set and may not collide with the first one, thus leading to a false positive.
-			// Is that possible? Investigate.
-			if _, found := s[key]; !found && (indirect || !ptrRecv(f)) {
-				s[key] = &Selection{MethodVal, nil, f, concat(index, i), indirect}
-				continue
-			}
-		}
-		s[key] = nil // collision
-	}
-	return s
-}
-
-// ptrRecv reports whether the receiver is of the form *T.
-func ptrRecv(f *Func) bool {
-	// If a method's receiver type is set, use that as the source of truth for the receiver.
-	// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
-	// signature. We may reach here before the signature is fully set up: we must explicitly
-	// check if the receiver is set (we cannot just look for non-nil f.typ).
-	if sig, _ := f.typ.(*Signature); sig != nil && sig.recv != nil {
-		_, isPtr := deref(sig.recv.typ)
-		return isPtr
-	}
-
-	// If a method's type is not set it may be a method/function that is:
-	// 1) client-supplied (via NewFunc with no signature), or
-	// 2) internally created but not yet type-checked.
-	// For case 1) we can't do anything; the client must know what they are doing.
-	// For case 2) we can use the information gathered by the resolver.
-	return f.hasPtrRecv
-}