re-bundle the latest version of typeutil.Hasher

And document how we do this and why.

CONTRIBUTING.md

@@ -105,6 +105,32 @@ the hash of the operation's inputs, and the last component is the *content ID*,
 the hash of the operation's output. For more, read
 [the docs in buildid.go](https://github.com/golang/go/blob/master/src/cmd/go/internal/work/buildid.go)
 
+### Bundled x/tools packages
+
+`bundled_typeutil.go` and `bundled_typeparams.go` are modified copies of x/tools packages.
+We need to modify [typeutil.Hasher](https://pkg.go.dev/golang.org/x/tools/go/types/typeutil#Hasher)
+so that it doesn't include struct field tags in the hash algorithm,
+given that struct field tags do not affect type identity.
+
+The typeutil package imports the internal `typeparams` package, so we must bundle that too,
+and replace the import with references to the bundled typeparams file.
+
+Our patches are marked via `// NOTE(garble)` and are done by hand.
+We also remove the `//go:generate` lines added by `bundle`
+because re-running the tool will undo the manual edits.
+
+Finally, we also remove any bundled API we don't need, that is,
+anything which is not reachable from the bundled `typeutil_Hasher` type.
+We also ensure that `staticcheck` does not report any unused code.
+
+To update these files to a newer x/tools version to gain upstream fixes:
+
+* `go get golang.org/x/tools@latest`
+* `go tool bundle -o bundled_typeutil.go golang.org/x/tools/go/types/typeutil`
+* `go tool bundle -o bundled_typeparams.go golang.org/x/tools/internal/typeparams`
+* re-apply the changes mentioned above
+* inspect the diff to ensure the changes look reasonable and we haven't lost any of our edits
+
 ### Benchmarking
 
 A build benchmark is available, to be able to measure the cost of builing a

bundled_typeparams.go

@@ -1,16 +1,20 @@
-// Originally bundled from golang.org/x/tools/internal/typeparams@v0.29.0,
+// NOTE(garble): bundled as of golang.org/x/tools v0.42.0; see CONTRIBUTING.md.
-// as it is used by x/tools/go/types/typeutil and is an internal package.
+
+//lint:file-ignore ST1012 NOTE(garble): err var names get a new prefix
 
 package main
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"go/types"
+	"os"
+	"strings"
 )
 
-var errEmptyTypeSet = errors.New("empty type set")
+const typeparams_debug = false
+
+var typeparams_ErrEmptyTypeSet = errors.New("empty type set")
 
 // InterfaceTermSet computes the normalized terms for a constraint interface,
 // returning an error if the term set cannot be computed or is empty. In the
@@ -38,7 +42,7 @@ func typeparams_computeTermSet(typ types.Type) ([]*types.Term, error) {
 		return nil, err
 	}
 	if tset.terms.isEmpty() {
-		return nil, errEmptyTypeSet
+		return nil, typeparams_ErrEmptyTypeSet
 	}
 	if tset.terms.isAll() {
 		return nil, nil
@@ -60,11 +64,26 @@ type typeparams_termSet struct {
 	terms    typeparams_termlist
 }
 
+func typeparams_indentf(depth int, format string, args ...any) {
+	fmt.Fprintf(os.Stderr, strings.Repeat(".", depth)+format+"\n", args...)
+}
+
 func typeparams_computeTermSetInternal(t types.Type, seen map[types.Type]*typeparams_termSet, depth int) (res *typeparams_termSet, err error) {
 	if t == nil {
 		panic("nil type")
 	}
 
+	if typeparams_debug {
+		typeparams_indentf(depth, "%s", t.String())
+		defer func() {
+			if err != nil {
+				typeparams_indentf(depth, "=> %s", err)
+			} else {
+				typeparams_indentf(depth, "=> %s", res.terms.String())
+			}
+		}()
+	}
+
 	const maxTermCount = 100
 	if tset, ok := seen[t]; ok {
 		if !tset.complete {
@@ -85,8 +104,7 @@ func typeparams_computeTermSetInternal(t types.Type, seen map[types.Type]*typepa
 		// The term set of an interface is the intersection of the term sets of its
 		// embedded types.
 		tset.terms = typeparams_allTermlist
-		for i := range u.NumEmbeddeds() {
+		for embedded := range u.EmbeddedTypes() {
-			embedded := u.EmbeddedType(i)
 			if _, ok := embedded.Underlying().(*types.TypeParam); ok {
 				return nil, fmt.Errorf("invalid embedded type %T", embedded)
 			}
@@ -99,8 +117,7 @@ func typeparams_computeTermSetInternal(t types.Type, seen map[types.Type]*typepa
 	case *types.Union:
 		// The term set of a union is the union of term sets of its terms.
 		tset.terms = nil
-		for i := range u.Len() {
+		for t := range u.Terms() {
-			t := u.Term(i)
 			var terms typeparams_termlist
 			switch t.Type().Underlying().(type) {
 			case *types.Interface:
@@ -156,15 +173,18 @@ type typeparams_termlist []*typeparams_term
 // It is in normal form.
 var typeparams_allTermlist = typeparams_termlist{new(typeparams_term)}
 
+// termSep is the separator used between individual terms.
+const typeparams_termSep = " | "
+
 // String prints the termlist exactly (without normalization).
 func (xl typeparams_termlist) String() string {
 	if len(xl) == 0 {
 		return "∅"
 	}
-	var buf bytes.Buffer
+	var buf strings.Builder
 	for i, x := range xl {
 		if i > 0 {
-			buf.WriteString(" | ")
+			buf.WriteString(typeparams_termSep)
 		}
 		buf.WriteString(x.String())
 	}
@@ -342,6 +362,9 @@ func (x *typeparams_term) intersect(y *typeparams_term) *typeparams_term {
 // disjoint reports whether x ∩ y == ∅.
 // x.typ and y.typ must not be nil.
 func (x *typeparams_term) disjoint(y *typeparams_term) bool {
+	if typeparams_debug && (x.typ == nil || y.typ == nil) {
+		panic("invalid argument(s)")
+	}
 	ux := x.typ
 	if y.tilde {
 		ux = typeparams_under(ux)

bundled_typeutil.go

@@ -1,12 +1,11 @@
-// Originally bundled from golang.org/x/tools/go/types/typeutil@v0.29.0.
+// NOTE(garble): bundled as of golang.org/x/tools v0.42.0; see CONTRIBUTING.md.
-// Edited to just keep the hasher API in place, removing the use of internal/typeparams,
-// and removed the inclusion of struct field tags in the hasher.
 
 package main
 
 import (
 	"fmt"
 	"go/types"
+	_ "unsafe"
 )
 
 // -- Hasher --
@@ -37,7 +36,7 @@ type typeutil_hasher struct{ inGenericSig bool }
 // hashString computes the Fowler–Noll–Vo hash of s.
 func typeutil_hashString(s string) uint32 {
 	var h uint32
-	for i := range len(s) {
+	for i := 0; i < len(s); i++ {
 		h ^= uint32(s[i])
 		h *= 16777619
 	}
@@ -67,7 +66,7 @@ func (h typeutil_hasher) hash(t types.Type) uint32 {
 			if f.Anonymous() {
 				hash += 8861
 			}
-			// NOTE: we must not hash struct field tags, as they do not affect type identity.
+			// NOTE(garble): we must not hash struct field tags, as they do not affect type identity.
 			// hash += typeutil_hashString(t.Tag(i))
 			hash += typeutil_hashString(f.Name()) // (ignore f.Pkg)
 			hash += h.hash(f.Type())
@@ -84,10 +83,13 @@ func (h typeutil_hasher) hash(t types.Type) uint32 {
 		}
 
 		tparams := t.TypeParams()
-		for i := range tparams.Len() {
+		if n := tparams.Len(); n > 0 {
-			h.inGenericSig = true
+			h.inGenericSig = true // affects constraints, params, and results
-			tparam := tparams.At(i)
+
-			hash += 7 * h.hash(tparam.Constraint())
+			for i := range n {
+				tparam := tparams.At(i)
+				hash += 7 * h.hash(tparam.Constraint())
+			}
 		}
 
 		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())
@@ -129,8 +131,7 @@ func (h typeutil_hasher) hash(t types.Type) uint32 {
 	case *types.Named:
 		hash := h.hashTypeName(t.Obj())
 		targs := t.TypeArgs()
-		for i := range targs.Len() {
+		for targ := range targs.Types() {
-			targ := targs.At(i)
 			hash += 2 * h.hash(targ)
 		}
 		return hash
@@ -200,21 +201,12 @@ func (h typeutil_hasher) hashTypeParam(t *types.TypeParam) uint32 {
 
 // hashTypeName hashes the pointer of tname.
 func (typeutil_hasher) hashTypeName(tname *types.TypeName) uint32 {
-	// NOTE: we must not hash any pointers, as garble is a toolexec tool
+	// NOTE(garble): we must not hash any pointers,
-	// so by nature it uses multiple processes.
+	// as garble is a toolexec tool so by nature it uses multiple processes.
 	return typeutil_hashString(tname.Name())
 	// Since types.Identical uses == to compare TypeNames,
 	// the Hash function uses maphash.Comparable.
-	// TODO(adonovan): or will, when it becomes available in go1.24.
+	// hash := maphash.Comparable(typeutil_theSeed, tname)
-	// In the meantime we use the pointer's numeric value.
-	//
-	//   hash := maphash.Comparable(theSeed, tname)
-	//
-	// (Another approach would be to hash the name and package
-	// path, and whether or not it is a package-level typename. It
-	// is rare for a package to define multiple local types with
-	// the same name.)
-	// hash := uintptr(unsafe.Pointer(tname))
 	// return uint32(hash ^ (hash >> 32))
 }