[tools/internal-branch.go1.26-vendor] [internal-branch.go1.26-vendor] go/analysis/passes/modernize: disable reflecttypefor modernizer for unnamed struct/interface
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Alan Donovan (Gerrit)
Dec 18, 2025, 3:25:09 PM (21 hours ago) Dec 18
to goph...@pubsubhelper.golang.org, Madeline Kalil, golang-co...@googlegroups.com
Alan Donovan has uploaded the change for review![]( "Open in Gerrit")
Commit message
[internal-branch.go1.26-vendor] go/analysis/passes/modernize: disable reflecttypefor modernizer for unnamed struct/interface
When a type contains an unnamed struct or an unnamed interface, we should
not suggest a fix because it will involve writing out the entire type and
will be more verbose than the existing code.
Fixes golang/go#76698
Change-Id: I5fdeb8dc5b7e70b2201fdf1fe714335aef439cc7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/726941
Reviewed-by: Alan Donovan <adon...@google.com>
LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>
(cherry picked from commit e5a08637a57b68119e771bf855e5bbbaeb37e8c2)
Change diff
diff --git a/go/analysis/passes/modernize/reflect.go b/go/analysis/passes/modernize/reflect.go
index 0fc7818..2611f6c 100644
--- a/go/analysis/passes/modernize/reflect.go
+++ b/go/analysis/passes/modernize/reflect.go
@@ -102,6 +102,23 @@
continue // e.g. reflect was dot-imported
}
+ // Don't offer a fix if the type contains an unnamed struct or unnamed
+ // interface because the replacement would be significantly more verbose.
+ // (See golang/go#76698)
+ if isComplicatedType(t) {
+ continue
+ }
+
+ // Don't offer the fix if the type string is too long. We define "too
+ // long" as more than three times the length of the original expression
+ // and at least 16 characters (a 3x length increase of a very
+ // short expression should not be cause for skipping the fix).
+ oldLen := int(expr.End() - expr.Pos())
+ newLen := len(tstr)
+ if newLen >= 16 && newLen > 3*oldLen {
+ continue
+ }
+
// If the call argument contains the last use
// of a variable, as in:
// var zero T
@@ -137,3 +154,43 @@
return nil, nil
}
+
+// isComplicatedType reports whether type t is complicated, e.g. it is or contains an
+// unnamed struct, interface, or function signature.
+func isComplicatedType(t types.Type) bool {
+ var check func(typ types.Type) bool
+ check = func(typ types.Type) bool {
+ switch t := typ.(type) {
+ case typesinternal.NamedOrAlias:
+ for ta := range t.TypeArgs().Types() {
+ if check(ta) {
+ return true
+ }
+ }
+ return false
+ case *types.Struct, *types.Interface, *types.Signature:
+ // These are complex types with potentially many elements
+ // so we should avoid duplicating their definition.
+ return true
+ case *types.Pointer:
+ return check(t.Elem())
+ case *types.Slice:
+ return check(t.Elem())
+ case *types.Array:
+ return check(t.Elem())
+ case *types.Chan:
+ return check(t.Elem())
+ case *types.Map:
+ return check(t.Key()) || check(t.Elem())
+ case *types.Basic:
+ return false
+ case *types.TypeParam:
+ return false
+ default:
+ // Includes types.Union
+ return true
+ }
+ }
+
+ return check(t)
+}
diff --git a/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go b/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go
index ee97a18..5e1a351 100644
--- a/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go
+++ b/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go
@@ -6,8 +6,14 @@
"time"
)
+type A string
+
+type B[T any] int
+
var (
x any
+ a A
+ b B[int]
_ = reflect.TypeOf(x) // nope (dynamic)
_ = reflect.TypeOf(0) // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeOf(uint(0)) // want "reflect.TypeOf call can be simplified using TypeFor"
@@ -18,6 +24,8 @@
_ = reflect.TypeOf(*new(time.Time)) // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeOf(time.Time{}) // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeOf(time.Duration(0)) // want "reflect.TypeOf call can be simplified using TypeFor"
+ _ = reflect.TypeOf(&a) // want "reflect.TypeOf call can be simplified using TypeFor"
+ _ = reflect.TypeOf(&b) // want "reflect.TypeOf call can be simplified using TypeFor"
)
// Eliminate local var if we deleted its last use.
@@ -29,3 +37,53 @@
_ = reflect.TypeOf(z2) // want "reflect.TypeOf call can be simplified using TypeFor"
_ = z2 // z2 has multiple uses
}
+
+type T struct {
+ f struct {
+ A bool
+ B int
+ C string
+ }
+}
+
+type S struct {
+ f [2]struct {
+ A bool
+ B int
+ C string
+ }
+}
+
+type R []struct {
+ A int
+}
+
+type M[T struct{ F int }] int
+
+type P struct {
+ f interface {
+ }
+ g func() // fine length
+
+ long func(a int, b int, c int) (bool, string, int) // too long
+
+ s func(a struct{})
+
+ q func() struct{}
+}
+
+func f(t *T, r R, m *M[struct{ F int }], s *S, p *P) {
+ // No suggested fix for all of the following because the type is complicated -- e.g. has an unnamed struct,
+ // interface, or signature -- so the fix would be more verbose than the original expression.
+ // Also because structs and interfaces often acquire new fields and methods, and the type string
+ // produced by this modernizer won't get updated automatically, potentially causing a bug.
+ _ = reflect.TypeOf(&t.f)
+ _ = reflect.TypeOf(r[0])
+ _ = reflect.TypeOf(m)
+ _ = reflect.TypeOf(&s.f)
+ _ = reflect.TypeOf(&p.f)
+ _ = reflect.TypeOf(&p.g)
+ _ = reflect.TypeOf(&p.long)
+ _ = reflect.TypeOf(&p.q)
+ _ = reflect.TypeOf(&p.s)
+}
diff --git a/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go.golden b/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go.golden
index 2f8f35a..7256f96 100644
--- a/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go.golden
+++ b/go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go.golden
@@ -6,8 +6,14 @@
"time"
)
+type A string
+
+type B[T any] int
+
var (
x any
+ a A
+ b B[int]
_ = reflect.TypeOf(x) // nope (dynamic)
_ = reflect.TypeFor[int]() // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeFor[uint]() // want "reflect.TypeOf call can be simplified using TypeFor"
@@ -18,6 +24,8 @@
_ = reflect.TypeFor[time.Time]() // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeFor[time.Time]() // want "reflect.TypeOf call can be simplified using TypeFor"
_ = reflect.TypeFor[time.Duration]() // want "reflect.TypeOf call can be simplified using TypeFor"
+ _ = reflect.TypeFor[*A]() // want "reflect.TypeOf call can be simplified using TypeFor"
+ _ = reflect.TypeFor[*B[int]]() // want "reflect.TypeOf call can be simplified using TypeFor"
)
// Eliminate local var if we deleted its last use.
@@ -28,3 +36,53 @@
_ = reflect.TypeFor[string]() // want "reflect.TypeOf call can be simplified using TypeFor"
_ = z2 // z2 has multiple uses
}
+
+type T struct {
+ f struct {
+ A bool
+ B int
+ C string
+ }
+}
+
+type S struct {
+ f [2]struct {
+ A bool
+ B int
+ C string
+ }
+}
+
+type R []struct {
+ A int
+}
+
+type M[T struct{ F int }] int
+
+type P struct {
+ f interface {
+ }
+ g func() // fine length
+
+ long func(a int, b int, c int) (bool, string, int) // too long
+
+ s func(a struct{})
+
+ q func() struct{}
+}
+
+func f(t *T, r R, m *M[struct{ F int }], s *S, p *P) {
+ // No suggested fix for all of the following because the type is complicated -- e.g. has an unnamed struct,
+ // interface, or signature -- so the fix would be more verbose than the original expression.
+ // Also because structs and interfaces often acquire new fields and methods, and the type string
+ // produced by this modernizer won't get updated automatically, potentially causing a bug.
+ _ = reflect.TypeOf(&t.f)
+ _ = reflect.TypeOf(r[0])
+ _ = reflect.TypeOf(m)
+ _ = reflect.TypeOf(&s.f)
+ _ = reflect.TypeOf(&p.f)
+ _ = reflect.TypeOf(&p.g)
+ _ = reflect.TypeOf(&p.long)
+ _ = reflect.TypeOf(&p.q)
+ _ = reflect.TypeOf(&p.s)
+}
Change information
Files:
- M go/analysis/passes/modernize/reflect.go
- M go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go
- M go/analysis/passes/modernize/testdata/src/reflecttypefor/reflecttypefor.go.golden
Change size: M
Delta: 3 files changed, 173 insertions(+), 0 deletions(-)
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Alan Donovan (Gerrit)
Dec 18, 2025, 3:26:17 PM (21 hours ago) Dec 18
to Madeline Kalil, goph...@pubsubhelper.golang.org, golang-co...@googlegroups.com
Alan Donovan voted Code-Review+2![]( "Open in Gerrit")
| Code-Review | +2 |
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Madeline Kalil (Gerrit)
Dec 18, 2025, 3:29:16 PM (21 hours ago) Dec 18
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Attention needed from Alan Donovan
Madeline Kalil voted Code-Review+2![]( "Open in Gerrit")
| Code-Review | +2 |
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Alan Donovan (Gerrit)
Dec 18, 2025, 5:01:31 PM (19 hours ago) Dec 18
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