[dev.simd] all: merge master (740857f) into dev.simd

Merge List:

+ 2025-06-30 740857f529 runtime: stash allpSnapshot on the M
+ 2025-06-30 9ae38be302 sync: disassociate WaitGroups from bubbles on Wait
+ 2025-06-30 4731832342 crypto/hmac: wrap ErrUnsupported returned by Clone
+ 2025-06-30 03ad694dcb runtime: update skips for TestGdbBacktrace
+ 2025-06-30 9d1cd0b881 iter: add missing type parameter in doc
+ 2025-06-29 acb914f2c2 cmd/doc: fix -http on Windows
+ 2025-06-27 b51f1cdb87 runtime: remove arbitrary 5-second timeout in TestNeedmDeadlock
+ 2025-06-27 f1e6ae2f6f reflect: fix TypeAssert on nil interface values
+ 2025-06-27 e81c624656 os: use minimal file permissions when opening parent directory in RemoveAll
+ 2025-06-27 2a22aefa1f encoding/json: add security section to doc
+ 2025-06-27 742fda9524 runtime: account for missing frame pointer in preamble
+ 2025-06-27 fdc076ce76 net/http: fix RoundTrip context cancellation for js/wasm
+ 2025-06-27 d9d2cadd63 encoding/json: fix typo in hotlink for jsontext.PreserveRawStrings
+ 2025-06-26 0f8ab2db17 cmd/link: permit a larger size BSS reference to a smaller DATA symbol
+ 2025-06-26 988a20c8c5 cmd/compile/internal/escape: evaluate any side effects when rewriting with literals
+ 2025-06-25 b5d555991a encoding/json/jsontext: remove Encoder.UnusedBuffer
+ 2025-06-25 0b4d2eab2f encoding/json/jsontext: rename Encoder.UnusedBuffer as Encoder.AvailableBuffer

Change-Id: Iea44ab825bdf087fbe7570df8d2d66d1d3327c31

src/cmd/cgo/internal/testsanitizers/asan_test.go

@@ -42,6 +42,8 @@ func TestASAN(t *testing.T) {
 		{src: "asan_global3_fail.go", memoryAccessError: "global-buffer-overflow", errorLocation: "asan_global3_fail.go:13"},
 		{src: "asan_global4_fail.go", memoryAccessError: "global-buffer-overflow", errorLocation: "asan_global4_fail.go:21"},
 		{src: "asan_global5.go"},
+		{src: "asan_global_asm"},
+		{src: "asan_global_asm2_fail", memoryAccessError: "global-buffer-overflow", errorLocation: "main.go:17"},
 		{src: "arena_fail.go", memoryAccessError: "use-after-poison", errorLocation: "arena_fail.go:26", experiments: []string{"arenas"}},
 	}
 	for _, tc := range cases {

src/cmd/cgo/internal/testsanitizers/cc_test.go

@@ -554,7 +554,7 @@ func (c *config) checkRuntime() (skip bool, err error) {
 
 // srcPath returns the path to the given file relative to this test's source tree.
 func srcPath(path string) string {
-	return filepath.Join("testdata", path)
+	return "./testdata/" + path
 }
 
 // A tempDir manages a temporary directory within a test.

src/cmd/cgo/internal/testsanitizers/testdata/asan_global_asm/asm.s

@@ -0,0 +1,8 @@
+// Copyright 2025 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.
+
+#include "textflag.h"
+
+DATA	·x(SB)/8, $123
+GLOBL	·x(SB), NOPTR, $8

src/cmd/cgo/internal/testsanitizers/testdata/asan_global_asm/main.go

@@ -0,0 +1,11 @@
+// Copyright 2025 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 main
+
+var x uint64
+
+func main() {
+	println(x)
+}

src/cmd/cgo/internal/testsanitizers/testdata/asan_global_asm2_fail/asm.s

@@ -0,0 +1,8 @@
+// Copyright 2025 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.
+
+#include "textflag.h"
+
+DATA	·x(SB)/8, $123
+GLOBL	·x(SB), NOPTR, $8

src/cmd/cgo/internal/testsanitizers/testdata/asan_global_asm2_fail/main.go

@@ -0,0 +1,20 @@
+// Copyright 2025 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 main
+
+import "unsafe"
+
+var x uint64
+
+func main() {
+	bar(&x)
+}
+
+func bar(a *uint64) {
+	p := (*uint64)(unsafe.Add(unsafe.Pointer(a), 1*unsafe.Sizeof(uint64(1))))
+	if *p == 10 { // BOOM
+		println("its value is 10")
+	}
+}

src/cmd/compile/internal/escape/escape.go

@@ -545,6 +545,14 @@ func (b *batch) rewriteWithLiterals(n ir.Node, fn *ir.Func) {
 		base.Fatalf("no ReassignOracle for function %v with closure parent %v", fn, fn.ClosureParent)
 	}
 
+	assignTemp := func(n ir.Node, init *ir.Nodes) {
+		// Preserve any side effects of n by assigning it to an otherwise unused temp.
+		pos := n.Pos()
+		tmp := typecheck.TempAt(pos, fn, n.Type())
+		init.Append(typecheck.Stmt(ir.NewDecl(pos, ir.ODCL, tmp)))
+		init.Append(typecheck.Stmt(ir.NewAssignStmt(pos, tmp, n)))
+	}
+
 	switch n.Op() {
 	case ir.OMAKESLICE:
 		// Check if we can replace a non-constant argument to make with
@@ -556,13 +564,17 @@ func (b *batch) rewriteWithLiterals(n ir.Node, fn *ir.Func) {
 			r = &n.Len
 		}
 
-		if s := ro.StaticValue(*r); s.Op() == ir.OLITERAL {
-			lit, ok := s.(*ir.BasicLit)
-			if !ok || lit.Val().Kind() != constant.Int {
-				base.Fatalf("unexpected BasicLit Kind")
-			}
-			if constant.Compare(lit.Val(), token.GEQ, constant.MakeInt64(0)) {
-				*r = lit
+		if (*r).Op() != ir.OLITERAL {
+			if s := ro.StaticValue(*r); s.Op() == ir.OLITERAL {
+				lit, ok := s.(*ir.BasicLit)
+				if !ok || lit.Val().Kind() != constant.Int {
+					base.Fatalf("unexpected BasicLit Kind")
+				}
+				if constant.Compare(lit.Val(), token.GEQ, constant.MakeInt64(0)) {
+					// Preserve any side effects of the original expression, then replace it.
+					assignTemp(*r, n.PtrInit())
+					*r = lit
+				}
 			}
 		}
 	case ir.OCONVIFACE:
@@ -575,6 +587,8 @@ func (b *batch) rewriteWithLiterals(n ir.Node, fn *ir.Func) {
 				if base.Debug.EscapeDebug >= 3 {
 					base.WarnfAt(n.Pos(), "rewriting OCONVIFACE value from %v (%v) to %v (%v)", conv.X, conv.X.Type(), v, v.Type())
 				}
+				// Preserve any side effects of the original expression, then replace it.
+				assignTemp(conv.X, conv.PtrInit())
 				v := v.(*ir.BasicLit)
 				conv.X = ir.NewBasicLit(conv.X.Pos(), conv.X.Type(), v.Val())
 				typecheck.Expr(conv)

src/cmd/go/alldocs.go

@@ -405,6 +405,8 @@
 //
 //	go doc
 //		Show documentation for current package.
+//	go doc -http
+//		Serve HTML documentation over HTTP for the current package.
 //	go doc Foo
 //		Show documentation for Foo in the current package.
 //		(Foo starts with a capital letter so it cannot match
@@ -439,26 +441,28 @@
 //
 // Flags:
 //
-//	-all
-//		Show all the documentation for the package.
-//	-c
-//		Respect case when matching symbols.
-//	-cmd
-//		Treat a command (package main) like a regular package.
-//		Otherwise package main's exported symbols are hidden
-//		when showing the package's top-level documentation.
-//	-short
-//		One-line representation for each symbol.
-//	-src
-//		Show the full source code for the symbol. This will
-//		display the full Go source of its declaration and
-//		definition, such as a function definition (including
-//		the body), type declaration or enclosing const
-//		block. The output may therefore include unexported
-//		details.
-//	-u
-//		Show documentation for unexported as well as exported
-//		symbols, methods, and fields.
+//		-all
+//			Show all the documentation for the package.
+//		-c
+//			Respect case when matching symbols.
+//		-cmd
+//			Treat a command (package main) like a regular package.
+//			Otherwise package main's exported symbols are hidden
+//			when showing the package's top-level documentation.
+//	  	-http
+//			Serve HTML docs over HTTP.
+//		-short
+//			One-line representation for each symbol.
+//		-src
+//			Show the full source code for the symbol. This will
+//			display the full Go source of its declaration and
+//			definition, such as a function definition (including
+//			the body), type declaration or enclosing const
+//			block. The output may therefore include unexported
+//			details.
+//		-u
+//			Show documentation for unexported as well as exported
+//			symbols, methods, and fields.
 //
 // # Print Go environment information
 //

src/cmd/go/internal/doc/doc.go

@@ -75,6 +75,8 @@ different cases. If this occurs, documentation for all matches is printed.
 Examples:
 	go doc
 		Show documentation for current package.
+	go doc -http
+		Serve HTML documentation over HTTP for the current package.
 	go doc Foo
 		Show documentation for Foo in the current package.
 		(Foo starts with a capital letter so it cannot match
@@ -116,6 +118,8 @@ Flags:
 		Treat a command (package main) like a regular package.
 		Otherwise package main's exported symbols are hidden
 		when showing the package's top-level documentation.
+  	-http
+		Serve HTML docs over HTTP.
 	-short
 		One-line representation for each symbol.
 	-src

src/cmd/internal/doc/main.go

@@ -227,8 +227,16 @@ func doPkgsite(urlPath string) error {
 	fields := strings.Fields(vars)
 	if err == nil && len(fields) == 2 {
 		goproxy, gomodcache := fields[0], fields[1]
-		goproxy = "file://" + filepath.Join(gomodcache, "cache", "download") + "," + goproxy
-		env = append(env, "GOPROXY="+goproxy)
+		gomodcache = filepath.Join(gomodcache, "cache", "download")
+		// Convert absolute path to file URL. pkgsite will not accept
+		// Windows absolute paths because they look like a host:path remote.
+		// TODO(golang.org/issue/32456): use url.FromFilePath when implemented.
+		if strings.HasPrefix(gomodcache, "/") {
+			gomodcache = "file://" + gomodcache
+		} else {
+			gomodcache = "file:///" + filepath.ToSlash(gomodcache)
+		}
+		env = append(env, "GOPROXY="+gomodcache+","+goproxy)
 	}
 
 	const version = "v0.0.0-20250608123103-82c52f1754cd"

src/cmd/link/internal/loader/loader.go

@@ -253,6 +253,12 @@ type Loader struct {
 
 	WasmExports []Sym
 
+	// sizeFixups records symbols that we need to fix up the size
+	// after loading. It is very rarely needed, only for a DATA symbol
+	// and a BSS symbol with the same name, and the BSS symbol has
+	// larger size.
+	sizeFixups []symAndSize
+
 	flags uint32
 
 	strictDupMsgs int // number of strict-dup warning/errors, when FlagStrictDups is enabled
@@ -469,18 +475,17 @@ func (st *loadState) addSym(name string, ver int, r *oReader, li uint32, kind in
 	// In summary, the "overwrite" variable and the final result are
 	//
 	// new sym       old sym       result
-	// ---------------------------------------------
+	// -------------------------------------------------------
 	// TEXT          BSS           new wins
 	// DATA          DATA          ERROR
 	// DATA lg/eq    BSS  sm/eq    new wins
-	// DATA small    BSS  large    ERROR
-	// BSS  large    DATA small    ERROR
+	// DATA small    BSS  large    merge: new with larger size
+	// BSS  large    DATA small    merge: old with larger size
 	// BSS  large    BSS  small    new wins
 	// BSS  sm/eq    D/B  lg/eq    old wins
 	// BSS           TEXT          old wins
 	oldtyp := sym.AbiSymKindToSymKind[objabi.SymKind(oldsym.Type())]
 	newtyp := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type())]
-	oldIsText := oldtyp.IsText()
 	newIsText := newtyp.IsText()
 	oldHasContent := oldr.DataSize(oldli) != 0
 	newHasContent := r.DataSize(li) != 0
@@ -488,12 +493,28 @@ func (st *loadState) addSym(name string, ver int, r *oReader, li uint32, kind in
 	newIsBSS := newtyp.IsData() && !newHasContent
 	switch {
 	case newIsText && oldIsBSS,
-		newHasContent && oldIsBSS && sz >= oldsz,
+		newHasContent && oldIsBSS,
 		newIsBSS && oldIsBSS && sz > oldsz:
 		// new symbol overwrites old symbol.
 		l.objSyms[oldi] = objSym{r.objidx, li}
-	case newIsBSS && (oldsz >= sz || oldIsText):
+		if oldsz > sz {
+			// If the BSS symbol has a larger size, expand the data
+			// symbol's size so access from the BSS side cannot overrun.
+			// It is hard to modify the symbol size until all Go objects
+			// (potentially read-only) are loaded, so we record it in
+			// a fixup table and apply them later. This is very rare.
+			// One case is a global variable with a Go declaration and an
+			// assembly definition, which typically have the same size,
+			// but in ASAN mode the Go declaration has a larger size due
+			// to the inserted red zone.
+			l.sizeFixups = append(l.sizeFixups, symAndSize{oldi, uint32(oldsz)})
+		}
+	case newIsBSS:
 		// old win, just ignore the new symbol.
+		if sz > oldsz {
+			// See the comment above for sizeFixups.
+			l.sizeFixups = append(l.sizeFixups, symAndSize{oldi, uint32(sz)})
+		}
 	default:
 		log.Fatalf("duplicated definition of symbol %s, from %s (type %s size %d) and %s (type %s size %d)", name, r.unit.Lib.Pkg, newtyp, sz, oldr.unit.Lib.Pkg, oldtyp, oldsz)
 	}
@@ -2277,6 +2298,10 @@ func (l *Loader) LoadSyms(arch *sys.Arch) {
 		st.preloadSyms(r, hashedDef)
 		st.preloadSyms(r, nonPkgDef)
 	}
+	for _, sf := range l.sizeFixups {
+		pp := l.cloneToExternal(sf.sym)
+		pp.size = int64(sf.size)
+	}
 	for _, vr := range st.linknameVarRefs {
 		l.checkLinkname(vr.pkg, vr.name, vr.sym)
 	}
@@ -2498,7 +2523,7 @@ func topLevelSym(sname string, skind sym.SymKind) bool {
 // a symbol originally discovered as part of an object file, it's
 // easier to do this if we make the updates to an external symbol
 // payload.
-func (l *Loader) cloneToExternal(symIdx Sym) {
+func (l *Loader) cloneToExternal(symIdx Sym) *extSymPayload {
 	if l.IsExternal(symIdx) {
 		panic("sym is already external, no need for clone")
 	}
@@ -2550,6 +2575,8 @@ func (l *Loader) cloneToExternal(symIdx Sym) {
 	// Some attributes were encoded in the object file. Copy them over.
 	l.SetAttrDuplicateOK(symIdx, r.Sym(li).Dupok())
 	l.SetAttrShared(symIdx, r.Shared())
+
+	return pp
 }
 
 // Copy the payload of symbol src to dst. Both src and dst must be external

src/crypto/hmac/hmac_test.go

@@ -11,6 +11,7 @@ import (
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
+	"errors"
 	"fmt"
 	"hash"
 	"testing"
@@ -583,6 +584,18 @@ func TestHMAC(t *testing.T) {
 	}
 }
 
+func TestNoClone(t *testing.T) {
+	h := New(func() hash.Hash { return justHash{sha256.New()} }, []byte("key"))
+	if _, ok := h.(hash.Cloner); !ok {
+		t.Skip("no Cloner support")
+	}
+	h.Write([]byte("test"))
+	_, err := h.(hash.Cloner).Clone()
+	if !errors.Is(err, errors.ErrUnsupported) {
+		t.Errorf("Clone() = %v, want ErrUnsupported", err)
+	}
+}
+
 func TestNonUniqueHash(t *testing.T) {
 	if boring.Enabled {
 		t.Skip("hash.Hash provided by boringcrypto are not comparable")

src/crypto/internal/fips140/hmac/hmac.go

@@ -130,26 +130,36 @@ func (h *HMAC) Reset() {
 	h.marshaled = true
 }
 
+type errCloneUnsupported struct{}
+
+func (e errCloneUnsupported) Error() string {
+	return "crypto/hmac: hash does not support hash.Cloner"
+}
+
+func (e errCloneUnsupported) Unwrap() error {
+	return errors.ErrUnsupported
+}
+
 // Clone implements [hash.Cloner] if the underlying hash does.
-// Otherwise, it returns [errors.ErrUnsupported].
+// Otherwise, it returns an error wrapping [errors.ErrUnsupported].
 func (h *HMAC) Clone() (hash.Cloner, error) {
 	r := *h
 	ic, ok := h.inner.(hash.Cloner)
 	if !ok {
-		return nil, errors.ErrUnsupported
+		return nil, errCloneUnsupported{}
 	}
 	oc, ok := h.outer.(hash.Cloner)
 	if !ok {
-		return nil, errors.ErrUnsupported
+		return nil, errCloneUnsupported{}
 	}
 	var err error
 	r.inner, err = ic.Clone()
 	if err != nil {
-		return nil, errors.ErrUnsupported
+		return nil, errCloneUnsupported{}
 	}
 	r.outer, err = oc.Clone()
 	if err != nil {
-		return nil, errors.ErrUnsupported
+		return nil, errCloneUnsupported{}
 	}
 	return &r, nil
 }

src/encoding/json/decode.go

@@ -43,11 +43,14 @@ import (
 // and the input is a JSON quoted string, Unmarshal calls
 // [encoding.TextUnmarshaler.UnmarshalText] with the unquoted form of the string.
 //
-// To unmarshal JSON into a struct, Unmarshal matches incoming object
-// keys to the keys used by [Marshal] (either the struct field name or its tag),
-// preferring an exact match but also accepting a case-insensitive match. By
-// default, object keys which don't have a corresponding struct field are
-// ignored (see [Decoder.DisallowUnknownFields] for an alternative).
+// To unmarshal JSON into a struct, Unmarshal matches incoming object keys to
+// the keys used by [Marshal] (either the struct field name or its tag),
+// ignoring case. If multiple struct fields match an object key, an exact case
+// match is preferred over a case-insensitive one.
+//
+// Incoming object members are processed in the order observed. If an object
+// includes duplicate keys, later duplicates will replace or be merged into
+// prior values.
 //
 // To unmarshal JSON into an interface value,
 // Unmarshal stores one of these in the interface value:

src/encoding/json/encode.go

@@ -4,12 +4,44 @@
 
 //go:build !goexperiment.jsonv2
 
-// Package json implements encoding and decoding of JSON as defined in
-// RFC 7159. The mapping between JSON and Go values is described
-// in the documentation for the Marshal and Unmarshal functions.
+// Package json implements encoding and decoding of JSON as defined in RFC 7159.
+// The mapping between JSON and Go values is described in the documentation for
+// the Marshal and Unmarshal functions.
 //
 // See "JSON and Go" for an introduction to this package:
 // https://golang.org/doc/articles/json_and_go.html
+//
+// # Security Considerations
+//
+// The JSON standard (RFC 7159) is lax in its definition of a number of parser
+// behaviors. As such, many JSON parsers behave differently in various
+// scenarios. These differences in parsers mean that systems that use multiple
+// independent JSON parser implementations may parse the same JSON object in
+// differing ways.
+//
+// Systems that rely on a JSON object being parsed consistently for security
+// purposes should be careful to understand the behaviors of this parser, as
+// well as how these behaviors may cause interoperability issues with other
+// parser implementations.
+//
+// Due to the Go Backwards Compatibility promise (https://go.dev/doc/go1compat)
+// there are a number of behaviors this package exhibits that may cause
+// interopability issues, but cannot be changed. In particular the following
+// parsing behaviors may cause issues:
+//
+//   - If a JSON object contains duplicate keys, keys are processed in the order
+//     they are observed, meaning later values will replace or be merged into
+//     prior values, depending on the field type (in particular maps and structs
+//     will have values merged, while other types have values replaced).
+//   - When parsing a JSON object into a Go struct, keys are considered in a
+//     case-insensitive fashion.
+//   - When parsing a JSON object into a Go struct, unknown keys in the JSON
+//     object are ignored (unless a [Decoder] is used and
+//     [Decoder.DisallowUnknownFields] has been called).
+//   - Invalid UTF-8 bytes in JSON strings are replaced by the Unicode
+//     replacement character.
+//   - Large JSON number integers will lose precision when unmarshaled into
+//     floating-point types.
 package json
 
 import (

src/encoding/json/jsontext/encode.go

@@ -74,8 +74,8 @@ type encodeBuffer struct {
 
 	// maxValue is the approximate maximum Value size passed to WriteValue.
 	maxValue int
-	// unusedCache is the buffer returned by the UnusedBuffer method.
-	unusedCache []byte
+	// availBuffer is the buffer returned by the AvailableBuffer method.
+	availBuffer []byte // always has zero length
 	// bufStats is statistics about buffer utilization.
 	// It is only used with pooled encoders in pools.go.
 	bufStats bufferStatistics
@@ -465,9 +465,9 @@ func (e *encoderState) AppendRaw(k Kind, safeASCII bool, appendFn func([]byte) (
 		isVerbatim := safeASCII || !jsonwire.NeedEscape(b[pos+len(`"`):len(b)-len(`"`)])
 		if !isVerbatim {
 			var err error
-			b2 := append(e.unusedCache, b[pos+len(`"`):len(b)-len(`"`)]...)
+			b2 := append(e.availBuffer, b[pos+len(`"`):len(b)-len(`"`)]...)
 			b, err = jsonwire.AppendQuote(b[:pos], string(b2), &e.Flags)
-			e.unusedCache = b2[:0]
+			e.availBuffer = b2[:0]
 			if err != nil {
 				return wrapSyntacticError(e, err, pos, +1)
 			}
@@ -900,20 +900,20 @@ func (e *Encoder) OutputOffset() int64 {
 	return e.s.previousOffsetEnd()
 }
 
-// UnusedBuffer returns a zero-length buffer with a possible non-zero capacity.
+// AvailableBuffer returns a zero-length buffer with a possible non-zero capacity.
 // This buffer is intended to be used to populate a [Value]
 // being passed to an immediately succeeding [Encoder.WriteValue] call.
 //
 // Example usage:
 //
-//	b := d.UnusedBuffer()
+//	b := d.AvailableBuffer()
 //	b = append(b, '"')
 //	b = appendString(b, v) // append the string formatting of v
 //	b = append(b, '"')
 //	... := d.WriteValue(b)
 //
 // It is the user's responsibility to ensure that the value is valid JSON.
-func (e *Encoder) UnusedBuffer() []byte {
+func (e *Encoder) AvailableBuffer() []byte {
 	// NOTE: We don't return e.buf[len(e.buf):cap(e.buf)] since WriteValue would
 	// need to take special care to avoid mangling the data while reformatting.
 	// WriteValue can't easily identify whether the input Value aliases e.buf
@@ -921,10 +921,10 @@ func (e *Encoder) UnusedBuffer() []byte {
 	// Should this ever alias e.buf, we need to consider how it operates with
 	// the specialized performance optimization for bytes.Buffer.
 	n := 1 << bits.Len(uint(e.s.maxValue|63)) // fast approximation for max length
-	if cap(e.s.unusedCache) < n {
-		e.s.unusedCache = make([]byte, 0, n)
+	if cap(e.s.availBuffer) < n {
+		e.s.availBuffer = make([]byte, 0, n)
 	}
-	return e.s.unusedCache
+	return e.s.availBuffer
 }
 
 // StackDepth returns the depth of the state machine for written JSON data.

src/encoding/json/v2/arshal_inlined.go

@@ -113,7 +113,7 @@ func marshalInlinedFallbackAll(enc *jsontext.Encoder, va addressableValue, mo *j
 		mk := newAddressableValue(m.Type().Key())
 		mv := newAddressableValue(m.Type().Elem())
 		marshalKey := func(mk addressableValue) error {
-			b, err := jsonwire.AppendQuote(enc.UnusedBuffer(), mk.String(), &mo.Flags)
+			b, err := jsonwire.AppendQuote(enc.AvailableBuffer(), mk.String(), &mo.Flags)
 			if err != nil {
 				return newMarshalErrorBefore(enc, m.Type().Key(), err)
 			}

src/encoding/json/v2_decode.go

@@ -199,7 +199,7 @@ func (n Number) MarshalJSONTo(enc *jsontext.Encoder) error {
 	}
 	n = cmp.Or(n, "0")
 	var num []byte
-	val := enc.UnusedBuffer()
+	val := enc.AvailableBuffer()
 	if stringify {
 		val = append(val, '"')
 		val = append(val, n...)

src/encoding/json/v2_options.go

@@ -221,7 +221,7 @@ type Options = jsonopts.Options
 //   - [jsontext.AllowInvalidUTF8]
 //   - [jsontext.EscapeForHTML]
 //   - [jsontext.EscapeForJS]
-//   - [jsontext.PreserveRawString]
+//   - [jsontext.PreserveRawStrings]
 //
 // All other boolean options are set to false.
 // All non-boolean options are set to the zero value,

src/hash/hash.go

@@ -57,13 +57,14 @@ type Hash64 interface {
 	Sum64() uint64
 }
 
-// A Cloner is a hash function whose state can be cloned.
+// A Cloner is a hash function whose state can be cloned, returning a value with
+// equivalent and independent state.
 //
 // All [Hash] implementations in the standard library implement this interface,
 // unless GOFIPS140=v1.0.0 is set.
 //
-// If a hash can only determine at runtime if it can be cloned,
-// (e.g., if it wraps another hash), it may return [errors.ErrUnsupported].
+// If a hash can only determine at runtime if it can be cloned (e.g. if it wraps
+// another hash), it may return an error wrapping [errors.ErrUnsupported].
 type Cloner interface {
 	Hash
 	Clone() (Cloner, error)

src/internal/synctest/synctest_test.go

@@ -654,6 +654,17 @@ func TestWaitGroupInBubble(t *testing.T) {
 	})
 }
 
+// https://go.dev/issue/74386
+func TestWaitGroupRacingAdds(t *testing.T) {
+	synctest.Run(func() {
+		var wg sync.WaitGroup
+		for range 100 {
+			wg.Go(func() {})
+		}
+		wg.Wait()
+	})
+}
+
 func TestWaitGroupOutOfBubble(t *testing.T) {
 	var wg sync.WaitGroup
 	wg.Add(1)
@@ -705,29 +716,35 @@ func TestWaitGroupMovedBetweenBubblesWithNonZeroCount(t *testing.T) {
 	})
 }
 
-func TestWaitGroupMovedBetweenBubblesWithZeroCount(t *testing.T) {
+func TestWaitGroupDisassociateInWait(t *testing.T) {
 	var wg sync.WaitGroup
 	synctest.Run(func() {
 		wg.Add(1)
 		wg.Done()
+		// Count and waiters are 0, so Wait disassociates the WaitGroup.
+		wg.Wait()
 	})
 	synctest.Run(func() {
-		// Reusing the WaitGroup is safe, because its count is zero.
+		// Reusing the WaitGroup is safe, because it is no longer bubbled.
 		wg.Add(1)
 		wg.Done()
 	})
 }
 
-func TestWaitGroupMovedBetweenBubblesAfterWait(t *testing.T) {
+func TestWaitGroupDisassociateInAdd(t *testing.T) {
 	var wg sync.WaitGroup
 	synctest.Run(func() {
-		wg.Go(func() {})
-		wg.Wait()
+		wg.Add(1)
+		go wg.Wait()
+		synctest.Wait() // wait for Wait to block
+		// Count is 0 and waiters != 0, so Done wakes the waiters and
+		// disassociates the WaitGroup.
+		wg.Done()
 	})
 	synctest.Run(func() {
-		// Reusing the WaitGroup is safe, because its count is zero.
-		wg.Go(func() {})
-		wg.Wait()
+		// Reusing the WaitGroup is safe, because it is no longer bubbled.
+		wg.Add(1)
+		wg.Done()
 	})
 }
 

src/internal/trace/testdata/testprog/stacks.go

@@ -97,6 +97,11 @@ func main() {
 		rp.Read(data[:])
 		pipeReadDone <- true
 	}()
+	go func() { // func12
+		for {
+			syncPreemptPoint()
+		}
+	}()
 
 	time.Sleep(100 * time.Millisecond)
 	runtime.GC()
@@ -127,3 +132,12 @@ func main() {
 
 	runtime.GOMAXPROCS(oldGoMaxProcs)
 }
+
+//go:noinline
+func syncPreemptPoint() {
+	if never {
+		syncPreemptPoint()
+	}
+}
+
+var never bool

src/internal/trace/trace_test.go

@@ -326,7 +326,8 @@ func TestTraceStacks(t *testing.T) {
 		const mainLine = 21
 		want := []evDesc{
 			{trace.EventStateTransition, "Goroutine Running->Runnable", []frame{
-				{"main.main", mainLine + 82},
+				{"runtime.Gosched", 0},
+				{"main.main", mainLine + 87},
 			}},
 			{trace.EventStateTransition, "Goroutine NotExist->Runnable", []frame{
 				{"main.main", mainLine + 11},
@@ -349,7 +350,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.chansend1", 0},
-				{"main.main", mainLine + 84},
+				{"main.main", mainLine + 89},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"runtime.chansend1", 0},
@@ -357,7 +358,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.chanrecv1", 0},
-				{"main.main", mainLine + 85},
+				{"main.main", mainLine + 90},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"runtime.selectgo", 0},
@@ -365,7 +366,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.selectgo", 0},
-				{"main.main", mainLine + 86},
+				{"main.main", mainLine + 91},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"sync.(*Mutex).Lock", 0},
@@ -382,7 +383,7 @@ func TestTraceStacks(t *testing.T) {
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"sync.(*WaitGroup).Add", 0},
 				{"sync.(*WaitGroup).Done", 0},
-				{"main.main", mainLine + 91},
+				{"main.main", mainLine + 96},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"sync.(*Cond).Wait", 0},
@@ -402,6 +403,10 @@ func TestTraceStacks(t *testing.T) {
 				{"runtime.GOMAXPROCS", 0},
 				{"main.main", 0},
 			}},
+			{trace.EventStateTransition, "Goroutine Running->Runnable", []frame{
+				{"main.syncPreemptPoint", 0},
+				{"main.main.func12", 0},
+			}},
 		}
 		if !stress {
 			// Only check for this stack if !stress because traceAdvance alone could

src/iter/iter.go

@@ -180,7 +180,7 @@ with the extra operations and then provide an iterator over positions.
 For example, a tree implementation might provide:
 
 	// Positions returns an iterator over positions in the sequence.
-	func (t *Tree[V]) Positions() iter.Seq[*Pos]
+	func (t *Tree[V]) Positions() iter.Seq[*Pos[V]]
 
 	// A Pos represents a position in the sequence.
 	// It is only valid during the yield call it is passed to.

src/net/http/roundtrip_js.go

@@ -236,6 +236,14 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 		if !ac.IsUndefined() {
 			// Abort the Fetch request.
 			ac.Call("abort")
+
+			// Wait for fetch promise to be rejected prior to exiting. See
+			// https://github.com/golang/go/issues/57098 for more details.
+			select {
+			case resp := <-respCh:
+				resp.Body.Close()
+			case <-errCh:
+			}
 		}
 		return nil, req.Context().Err()
 	case resp := <-respCh:

src/os/removeall_at.go

@@ -8,6 +8,7 @@ package os
 
 import (
 	"io"
+	"runtime"
 	"syscall"
 )
 
@@ -34,7 +35,15 @@ func removeAll(path string) error {
 	// its parent directory
 	parentDir, base := splitPath(path)
 
-	parent, err := Open(parentDir)
+	flag := O_RDONLY
+	if runtime.GOOS == "windows" {
+		// On Windows, the process might not have read permission on the parent directory,
+		// but still can delete files in it. See https://go.dev/issue/74134.
+		// We can open a file even if we don't have read permission by passing the
+		// O_WRONLY | O_RDWR flag, which is mapped to FILE_READ_ATTRIBUTES.
+		flag = O_WRONLY | O_RDWR
+	}
+	parent, err := OpenFile(parentDir, flag, 0)
 	if IsNotExist(err) {
 		// If parent does not exist, base cannot exist. Fail silently
 		return nil

src/reflect/all_test.go

@@ -8719,6 +8719,11 @@ func TestTypeAssert(t *testing.T) {
 	testTypeAssert(t, any(int(1)), int(1), true)
 	testTypeAssert(t, any(int(1)), byte(0), false)
 	testTypeAssert(t, fmt.Stringer(vv), vv, true)
+
+	testTypeAssert(t, any(nil), any(nil), false)
+	testTypeAssert(t, any(nil), error(nil), false)
+	testTypeAssert(t, error(nil), any(nil), false)
+	testTypeAssert(t, error(nil), error(nil), false)
 }
 
 func testTypeAssert[T comparable, V any](t *testing.T, val V, wantVal T, wantOk bool) {

src/reflect/value.go

@@ -1514,46 +1514,46 @@ func TypeAssert[T any](v Value) (T, bool) {
 	}
 
 	typ := abi.TypeFor[T]()
+
+	// If v is an interface, return the element inside the interface.
+	//
+	// T is a concrete type and v is an interface. For example:
+	//
+	//	var v any = int(1)
+	//	val := ValueOf(&v).Elem()
+	//	TypeAssert[int](val) == val.Interface().(int)
+	//
+	// T is a interface and v is a non-nil interface value. For example:
+	//
+	//	var v any = &someError{}
+	//	val := ValueOf(&v).Elem()
+	//	TypeAssert[error](val) == val.Interface().(error)
+	//
+	// T is a interface and v is a nil interface value. For example:
+	//
+	//	var v error = nil
+	//	val := ValueOf(&v).Elem()
+	//	TypeAssert[error](val) == val.Interface().(error)
+	if v.kind() == Interface {
+		v, ok := packIfaceValueIntoEmptyIface(v).(T)
+		return v, ok
+	}
+
+	// If T is an interface and v is a concrete type. For example:
+	//
+	//	TypeAssert[any](ValueOf(1)) == ValueOf(1).Interface().(any)
+	//	TypeAssert[error](ValueOf(&someError{})) == ValueOf(&someError{}).Interface().(error)
+	if typ.Kind() == abi.Interface {
+		v, ok := packEface(v).(T)
+		return v, ok
+	}
+
+	// Both v and T must be concrete types.
+	// The only way for an type-assertion to match is if the types are equal.
 	if typ != v.typ() {
-		// We can't just return false here:
-		//
-		//	var zero T
-		//	return zero, false
-		//
-		// since this function should work in the same manner as v.Interface().(T) does.
-		// Thus we have to handle two cases specially.
-
-		// Return the element inside the interface.
-		//
-		// T is a concrete type and v is an interface. For example:
-		//
-		// var v any = int(1)
-		// val := ValueOf(&v).Elem()
-		// TypeAssert[int](val) == val.Interface().(int)
-		//
-		// T is a interface and v is an interface, but the iface types are different. For example:
-		//
-		// var v any = &someError{}
-		// val := ValueOf(&v).Elem()
-		// TypeAssert[error](val) == val.Interface().(error)
-		if v.kind() == Interface {
-			v, ok := packIfaceValueIntoEmptyIface(v).(T)
-			return v, ok
-		}
-
-		// T is an interface, v is a concrete type. For example:
-		//
-		// TypeAssert[any](ValueOf(1)) == ValueOf(1).Interface().(any)
-		// TypeAssert[error](ValueOf(&someError{})) == ValueOf(&someError{}).Interface().(error)
-		if typ.Kind() == abi.Interface {
-			v, ok := packEface(v).(T)
-			return v, ok
-		}
-
 		var zero T
 		return zero, false
 	}
-
 	if v.flag&flagIndir == 0 {
 		return *(*T)(unsafe.Pointer(&v.ptr)), true
 	}

src/runtime/proc.go

@@ -1059,6 +1059,28 @@ func (mp *m) becomeSpinning() {
 	sched.needspinning.Store(0)
 }
 
+// Take a snapshot of allp, for use after dropping the P.
+//
+// Must be called with a P, but the returned slice may be used after dropping
+// the P. The M holds a reference on the snapshot to keep the backing array
+// alive.
+//
+//go:yeswritebarrierrec
+func (mp *m) snapshotAllp() []*p {
+	mp.allpSnapshot = allp
+	return mp.allpSnapshot
+}
+
+// Clear the saved allp snapshot. Should be called as soon as the snapshot is
+// no longer required.
+//
+// Must be called after reacquiring a P, as it requires a write barrier.
+//
+//go:yeswritebarrierrec
+func (mp *m) clearAllpSnapshot() {
+	mp.allpSnapshot = nil
+}
+
 func (mp *m) hasCgoOnStack() bool {
 	return mp.ncgo > 0 || mp.isextra
 }
@@ -3307,10 +3329,10 @@ func execute(gp *g, inheritTime bool) {
 		tryRecordGoroutineProfile(gp, nil, osyield)
 	}
 
-	// Assign gp.m before entering _Grunning so running Gs have an
-	// M.
+	// Assign gp.m before entering _Grunning so running Gs have an M.
 	mp.curg = gp
 	gp.m = mp
+	gp.syncSafePoint = false // Clear the flag, which may have been set by morestack.
 	casgstatus(gp, _Grunnable, _Grunning)
 	gp.waitsince = 0
 	gp.preempt = false
@@ -3346,6 +3368,11 @@ func findRunnable() (gp *g, inheritTime, tryWakeP bool) {
 	// an M.
 
 top:
+	// We may have collected an allp snapshot below. The snapshot is only
+	// required in each loop iteration. Clear it to all GC to collect the
+	// slice.
+	mp.clearAllpSnapshot()
+
 	pp := mp.p.ptr()
 	if sched.gcwaiting.Load() {
 		gcstopm()
@@ -3527,7 +3554,11 @@ top:
 	// which can change underfoot once we no longer block
 	// safe-points. We don't need to snapshot the contents because
 	// everything up to cap(allp) is immutable.
-	allpSnapshot := allp
+	//
+	// We clear the snapshot from the M after return via
+	// mp.clearAllpSnapshop (in schedule) and on each iteration of the top
+	// loop.
+	allpSnapshot := mp.snapshotAllp()
 	// Also snapshot masks. Value changes are OK, but we can't allow
 	// len to change out from under us.
 	idlepMaskSnapshot := idlepMask
@@ -3668,6 +3699,9 @@ top:
 		pollUntil = checkTimersNoP(allpSnapshot, timerpMaskSnapshot, pollUntil)
 	}
 
+	// We don't need allp anymore at this pointer, but can't clear the
+	// snapshot without a P for the write barrier..
+
 	// Poll network until next timer.
 	if netpollinited() && (netpollAnyWaiters() || pollUntil != 0) && sched.lastpoll.Swap(0) != 0 {
 		sched.pollUntil.Store(pollUntil)
@@ -4103,6 +4137,11 @@ top:
 
 	gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available
 
+	// findRunnable may have collected an allp snapshot. The snapshot is
+	// only required within findRunnable. Clear it to all GC to collect the
+	// slice.
+	mp.clearAllpSnapshot()
+
 	if debug.dontfreezetheworld > 0 && freezing.Load() {
 		// See comment in freezetheworld. We don't want to perturb
 		// scheduler state, so we didn't gcstopm in findRunnable, but

src/runtime/runtime-gdb_test.go

@@ -528,11 +528,12 @@ func TestGdbBacktrace(t *testing.T) {
 	got, err := cmd.CombinedOutput()
 	t.Logf("gdb output:\n%s", got)
 	if err != nil {
+		noProcessRE := regexp.MustCompile(`Couldn't get [a-zA-Z_ -]* ?registers: No such process\.`)
 		switch {
 		case bytes.Contains(got, []byte("internal-error: wait returned unexpected status 0x0")):
 			// GDB bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28551
 			testenv.SkipFlaky(t, 43068)
-		case bytes.Contains(got, []byte("Couldn't get registers: No such process.")),
+		case noProcessRE.Match(got),
 			bytes.Contains(got, []byte("Unable to fetch general registers.: No such process.")),
 			bytes.Contains(got, []byte("reading register pc (#64): No such process.")):
 			// GDB bug: https://sourceware.org/bugzilla/show_bug.cgi?id=9086

src/runtime/runtime2.go

@@ -466,6 +466,7 @@ type g struct {
 	runnableTime    int64 // the amount of time spent runnable, cleared when running, only used when tracking
 	lockedm         muintptr
 	fipsIndicator   uint8
+	syncSafePoint   bool // set if g is stopped at a synchronous safe point.
 	runningCleanups atomic.Bool
 	sig             uint32
 	writebuf        []byte
@@ -568,6 +569,7 @@ type m struct {
 	needextram      bool
 	g0StackAccurate bool // whether the g0 stack has accurate bounds
 	traceback       uint8
+	allpSnapshot    []*p          // Snapshot of allp for use after dropping P in findRunnable, nil otherwise.
 	ncgocall        uint64        // number of cgo calls in total
 	ncgo            int32         // number of cgo calls currently in progress
 	cgoCallersUse   atomic.Uint32 // if non-zero, cgoCallers in use temporarily

src/runtime/stack.go

@@ -1115,6 +1115,9 @@ func newstack() {
 			shrinkstack(gp)
 		}
 
+		// Set a flag indicated that we've been synchronously preempted.
+		gp.syncSafePoint = true
+
 		if gp.preemptStop {
 			preemptPark(gp) // never returns
 		}

src/runtime/testdata/testprogcgo/needmdeadlock.go

@@ -70,8 +70,6 @@ import "C"
 
 import (
 	"fmt"
-	"os"
-	"time"
 )
 
 func init() {
@@ -84,12 +82,8 @@ func GoNeedM() {
 
 func NeedmDeadlock() {
 	// The failure symptom is that the program hangs because of a
-	// deadlock in needm, so set an alarm.
-	go func() {
-		time.Sleep(5 * time.Second)
-		fmt.Println("Hung for 5 seconds")
-		os.Exit(1)
-	}()
+	// deadlock in needm. Instead of using an arbitrary timeout,
+	// we let the test deadline expire if it deadlocks.
 
 	C.runNeedmSignalThread()
 	fmt.Println("OK")

src/runtime/traceruntime.go

@@ -457,7 +457,7 @@ func (tl traceLocker) GoPreempt() {
 
 // GoStop emits a GoStop event with the provided reason.
 func (tl traceLocker) GoStop(reason traceGoStopReason) {
-	tl.eventWriter(tracev2.GoRunning, tracev2.ProcRunning).event(tracev2.EvGoStop, traceArg(trace.goStopReasons[tl.gen%2][reason]), tl.stack(1))
+	tl.eventWriter(tracev2.GoRunning, tracev2.ProcRunning).event(tracev2.EvGoStop, traceArg(trace.goStopReasons[tl.gen%2][reason]), tl.stack(0))
 }
 
 // GoPark emits a GoBlock event with the provided reason.

src/runtime/tracestack.go

@@ -109,7 +109,22 @@ func traceStack(skip int, gp *g, gen uintptr) uint64 {
 				nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.syscallbp), pcBuf[2:])
 			} else {
 				pcBuf[1] = gp.sched.pc
-				nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[2:])
+				if gp.syncSafePoint {
+					// We're stopped in morestack, which is an odd state because gp.sched.bp
+					// refers to our parent frame, since we haven't had the chance to push our
+					// frame pointer to the stack yet. If we just start walking from gp.sched.bp,
+					// we'll skip a frame as a result. Luckily, we can find the PC we want right
+					// at gp.sched.sp on non-LR platforms, and we have it directly on LR platforms.
+					// See issue go.dev/issue/68090.
+					if usesLR {
+						pcBuf[2] = gp.sched.lr
+					} else {
+						pcBuf[2] = *(*uintptr)(unsafe.Pointer(gp.sched.sp))
+					}
+					nstk += 2 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[3:])
+				} else {
+					nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[2:])
+				}
 			}
 		}
 	}

src/sync/waitgroup.go

@@ -120,13 +120,6 @@ func (wg *WaitGroup) Add(delta int) {
 	if w != 0 && delta > 0 && v == int32(delta) {
 		panic("sync: WaitGroup misuse: Add called concurrently with Wait")
 	}
-	if v == 0 && bubbled {
-		// Disassociate the WaitGroup from its bubble.
-		synctest.Disassociate(wg)
-		if w == 0 {
-			wg.state.Store(0)
-		}
-	}
 	if v > 0 || w == 0 {
 		return
 	}
@@ -140,6 +133,11 @@ func (wg *WaitGroup) Add(delta int) {
 	}
 	// Reset waiters count to 0.
 	wg.state.Store(0)
+	if bubbled {
+		// Adds must not happen concurrently with wait when counter is 0,
+		// so we can safely disassociate wg from its current bubble.
+		synctest.Disassociate(wg)
+	}
 	for ; w != 0; w-- {
 		runtime_Semrelease(&wg.sema, false, 0)
 	}
@@ -166,13 +164,20 @@ func (wg *WaitGroup) Wait() {
 	for {
 		state := wg.state.Load()
 		v := int32(state >> 32)
-		w := uint32(state)
+		w := uint32(state & 0x7fffffff)
 		if v == 0 {
 			// Counter is 0, no need to wait.
 			if race.Enabled {
 				race.Enable()
 				race.Acquire(unsafe.Pointer(wg))
 			}
+			if w == 0 && state&waitGroupBubbleFlag != 0 && synctest.IsAssociated(wg) {
+				// Adds must not happen concurrently with wait when counter is 0,
+				// so we can disassociate wg from its current bubble.
+				if wg.state.CompareAndSwap(state, 0) {
+					synctest.Disassociate(wg)
+				}
+			}
 			return
 		}
 		// Increment waiters count.

test/fixedbugs/issue74379.go

@@ -0,0 +1,30 @@
+// run
+
+// Copyright 2025 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 main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+func crashOnErr(err error) bool {
+	if err != nil {
+		panic(err)
+	}
+	return false
+}
+
+func main() {
+	defer func() {
+		if recover() == nil {
+			fmt.Println("failed to have expected panic")
+			os.Exit(1)
+		}
+	}()
+	fmt.Println(crashOnErr(errors.New("test error")))
+}

test/fixedbugs/issue74379b.go

@@ -0,0 +1,32 @@
+// run
+
+// Copyright 2025 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 main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+func crashOnErr(err error) int {
+	if err != nil {
+		panic(err)
+	}
+	return 10
+}
+
+func main() {
+	defer func() {
+		if recover() == nil {
+			fmt.Println("failed to have expected panic")
+			os.Exit(1)
+		}
+	}()
+
+	s := make([]int, crashOnErr(errors.New("test error")))
+	println("unreachable: len(s) =", len(s))
+}

test/fixedbugs/issue74379c.go

@@ -0,0 +1,54 @@
+// run
+
+// Copyright 2025 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 main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+)
+
+type S struct{ a, b int }
+
+func crashOnErr1(err error) S {
+	if err != nil {
+		panic(err)
+	}
+	return S{} // zero value struct
+}
+
+func f1() {
+	defer func() {
+		if recover() == nil {
+			fmt.Println("failed to have expected panic")
+			os.Exit(1)
+		}
+	}()
+	fmt.Println(crashOnErr1(errors.New("test error")))
+}
+
+func crashOnErr2(err error) S {
+	if err != nil {
+		panic(err)
+	}
+	return S{1, 2} // not zero value struct
+}
+
+func f2() {
+	defer func() {
+		if recover() == nil {
+			fmt.Println("failed to have expected panic")
+			os.Exit(1)
+		}
+	}()
+	fmt.Println(crashOnErr2(errors.New("test error")))
+}
+
+func main() {
+	f1()
+	f2()
+}