[release-branch.go1.21] all: merge master (2639a17) into release-branch.go1.21

Change-Id: I316578aec6c2b618c840d43a65ef87b8d2168ac0

19 files changed, 217 insertions, 112 deletions

diff --git a/doc/go1.21.html b/doc/go1.21.html
index 6c58cb0590..97d73720f2 100644
--- a/doc/go1.21.html
+++ b/doc/go1.21.html
@@ -328,7 +328,7 @@ Do not send CLs removing the interior tags from such phrases.
 <h2 id="linker">Linker</h2>
 
 <p><!-- https://go.dev/issue/57302, CL 461749, CL 457455 -->
-  On Windows AMD64, the linker (with help from the compiler) now emits
+  On windows/amd64, the linker (with help from the compiler) now emits
   SEH unwinding data by default, which improves the integration
   of Go applications with Windows debuggers and other tools.
 </p>
@@ -346,8 +346,8 @@ Do not send CLs removing the interior tags from such phrases.
 <h3 id="slog">New log/slog package</h3>
 
 <p><!-- https://go.dev/issue/59060, https://go.dev/issue/59141, https://go.dev/issue/59204, https://go.dev/issue/59280,
-        https://go.dev/issue/59282, https://go.dev/issue/59339, https://go.dev/issue/59345,
-        CL 477295, CL 484096, CL 486376, CL 486415, CL 487855 -->
+        https://go.dev/issue/59282, https://go.dev/issue/59339, https://go.dev/issue/59345, https://go.dev/issue/61200,
+        CL 477295, CL 484096, CL 486376, CL 486415, CL 487855, CL 508195 -->
   The new <a href="/pkg/log/slog">log/slog</a> package provides structured logging with levels.
   Structured logging emits key-value pairs
   to enable fast, accurate processing of large amounts of log data.
@@ -367,7 +367,8 @@ Do not send CLs removing the interior tags from such phrases.
   <!-- https://go.dev/issue/45955, https://go.dev/issue/54768 -->
   <!-- https://go.dev/issue/57348, https://go.dev/issue/57433 -->
   <!-- https://go.dev/issue/58565, https://go.dev/issue/60091 -->
-  <!-- CL 467417, CL 468855, CL 483175, CL 496078, CL 498175 -->
+  <!-- https://go.dev/issue/60546 -->
+  <!-- CL 467417, CL 468855, CL 483175, CL 496078, CL 498175, CL 502955 -->
   The new <a href="/pkg/slices">slices</a> package provides many common
   operations on slices, using generic functions that work with slices
   of any element type.
@@ -755,6 +756,14 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl><!-- go/token -->
 
+<dl id="go/types"><dt><a href="/pkg/go/types/">go/types</a></dt>
+  <dd>
+    <p><!-- https://go.dev/issue/61175, CL 507975 -->
+      TODO: <a href="https://go.dev/cl/507975">https://go.dev/cl/507975</a>: go/types: record Config.GoVersion for reporting in Package.GoVersion method; modified api/go1.21.txt
+    </p>
+  </dd>
+</dl><!-- go/types -->
+
 <dl id="hash/maphash"><dt><a href="/pkg/hash/maphash/">hash/maphash</a></dt>
   <dd>
     <p><!-- https://go.dev/issue/47342, CL 468795 -->
@@ -1235,18 +1244,21 @@ Do not send CLs removing the interior tags from such phrases.
   <code>c-archive</code>, <code>c-shared</code>, <code>shared</code>, <code>pie</code>, <code>plugin</code>.
 </p>
 
-
 <!-- proposals for x repos that don't need to be mentioned here but
      are picked up by the relnote tool. -->
 <!-- https://go.dev/issue/54232 -->
+<!-- https://go.dev/issue/57051 -->
 <!-- https://go.dev/issue/57792 -->
 <!-- https://go.dev/issue/57906 -->
 <!-- https://go.dev/issue/58668 -->
+<!-- https://go.dev/issue/59016 -->
 <!-- https://go.dev/issue/59676 -->
+<!-- https://go.dev/issue/60409 -->
+<!-- https://go.dev/issue/61176 -->
 
 <!-- changes to cmd/api that don't need release notes. -->
 <!-- CL 469115, CL 469135, CL 499981 -->
 
-<!-- proposals that don't need release enotes. -->
+<!-- proposals that don't need release notes. -->
 <!-- https://go.dev/issue/10275 -->
 <!-- https://go.dev/issue/59719 -->
diff --git a/src/bytes/compare_test.go b/src/bytes/compare_test.go
index ac39f880f4..067530b6d8 100644
--- a/src/bytes/compare_test.go
+++ b/src/bytes/compare_test.go
@@ -7,7 +7,6 @@ package bytes_test
 import (
 	. "bytes"
 	"fmt"
-	"internal/testenv"
 	"testing"
 )
 
@@ -73,7 +72,7 @@ func TestCompareBytes(t *testing.T) {
 	}
 	lengths = append(lengths, 256, 512, 1024, 1333, 4095, 4096, 4097)
 
-	if !testing.Short() || testenv.Builder() != "" {
+	if !testing.Short() {
 		lengths = append(lengths, 65535, 65536, 65537, 99999)
 	}
 
diff --git a/src/cmd/compile/internal/types2/const.go b/src/cmd/compile/internal/types2/const.go
index 9be578c647..af27c727dd 100644
--- a/src/cmd/compile/internal/types2/const.go
+++ b/src/cmd/compile/internal/types2/const.go
@@ -73,7 +73,6 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 
 	sizeof := func(T Type) int64 {
 		s := conf.sizeof(T)
-		assert(s == 4 || s == 8)
 		return s
 	}
 
diff --git a/src/cmd/covdata/doc.go b/src/cmd/covdata/doc.go
index 924a742ed5..1836bb833c 100644
--- a/src/cmd/covdata/doc.go
+++ b/src/cmd/covdata/doc.go
@@ -3,82 +3,78 @@
 // license that can be found in the LICENSE file.
 
 /*
-//
-// Covdata is a program for manipulating and generating reports
-// from 2nd-generation coverage testing output files, those produced
-// from running applications or integration tests. E.g.
-//
-//		$ mkdir ./profiledir
-//		$ go build -cover -o myapp.exe .
-//		$ GOCOVERDIR=./profiledir ./myapp.exe <arguments>
-//		$ ls ./profiledir
-//		covcounters.cce1b350af34b6d0fb59cc1725f0ee27.821598.1663006712821344241
-//		covmeta.cce1b350af34b6d0fb59cc1725f0ee27
-//		$
-//
-// Run covdata via "go tool covdata <mode>", where 'mode' is a subcommand
-// selecting a specific reporting, merging, or data manipulation operation.
-// Descriptions on the various modes (run "go tool cover <mode> -help" for
-// specifics on usage of a given mode:
-//
-// 1. Report percent of statements covered in each profiled package
-//
-//		$ go tool covdata percent -i=profiledir
-//		cov-example/p	coverage: 41.1% of statements
-//		main	coverage: 87.5% of statements
-//      $
-//
-//
-// 2. Report import paths of packages profiled
-//
-//		$ go tool covdata pkglist -i=profiledir
-//		cov-example/p
-//		main
-//      $
-//
-// 3. Report percent statements covered by function:
-//
-//		$ go tool covdata func -i=profiledir
-//		cov-example/p/p.go:12:		emptyFn			0.0%
-//		cov-example/p/p.go:32:		Small			100.0%
-//		cov-example/p/p.go:47:		Medium			90.9%
-//      ...
-//      $
-//
-// 4. Convert coverage data to legacy textual format:
-//
-//		$ go tool covdata textfmt -i=profiledir -o=cov.txt
-//      $ head cov.txt
-//      mode: set
-//      cov-example/p/p.go:12.22,13.2 0 0
-//      cov-example/p/p.go:15.31,16.2 1 0
-//      cov-example/p/p.go:16.3,18.3 0 0
-//      cov-example/p/p.go:19.3,21.3 0 0
-//      ...
-//      $ go tool cover -html=cov.txt
-//      $
-//
-// 5. Merge profiles together:
-//
-//		$ go tool covdata merge -i=indir1,indir2 -o=outdir -modpaths=github.com/go-delve/delve
-//      $
-//
-// 6. Subtract one profile from another
-//
-//		$ go tool covdata subtract -i=indir1,indir2 -o=outdir
-//      $
-//
-// 7. Intersect profiles
-//
-//		$ go tool covdata intersect -i=indir1,indir2 -o=outdir
-//      $
-//
-// 8. Dump a profile for debugging purposes.
-//
-//		$ go tool covdata debugdump -i=indir
-//      <human readable output>
-//      $
-//
-*/
+Covdata is a program for manipulating and generating reports
+from 2nd-generation coverage testing output files, those produced
+from running applications or integration tests. E.g.
+
+	$ mkdir ./profiledir
+	$ go build -cover -o myapp.exe .
+	$ GOCOVERDIR=./profiledir ./myapp.exe <arguments>
+	$ ls ./profiledir
+	covcounters.cce1b350af34b6d0fb59cc1725f0ee27.821598.1663006712821344241
+	covmeta.cce1b350af34b6d0fb59cc1725f0ee27
+	$
+
+Run covdata via "go tool covdata <mode>", where 'mode' is a subcommand
+selecting a specific reporting, merging, or data manipulation operation.
+Descriptions on the various modes (run "go tool cover <mode> -help" for
+specifics on usage of a given mode:
+
+1. Report percent of statements covered in each profiled package
+
+	$ go tool covdata percent -i=profiledir
+	cov-example/p	coverage: 41.1% of statements
+	main	coverage: 87.5% of statements
+	$
+
+2. Report import paths of packages profiled
+
+	$ go tool covdata pkglist -i=profiledir
+	cov-example/p
+	main
+	$
+
+3. Report percent statements covered by function:
+
+	$ go tool covdata func -i=profiledir
+	cov-example/p/p.go:12:		emptyFn			0.0%
+	cov-example/p/p.go:32:		Small			100.0%
+	cov-example/p/p.go:47:		Medium			90.9%
+	...
+	$
+
+4. Convert coverage data to legacy textual format:
 
+	$ go tool covdata textfmt -i=profiledir -o=cov.txt
+	$ head cov.txt
+	mode: set
+	cov-example/p/p.go:12.22,13.2 0 0
+	cov-example/p/p.go:15.31,16.2 1 0
+	cov-example/p/p.go:16.3,18.3 0 0
+	cov-example/p/p.go:19.3,21.3 0 0
+	...
+	$ go tool cover -html=cov.txt
+	$
+
+5. Merge profiles together:
+
+	$ go tool covdata merge -i=indir1,indir2 -o=outdir -modpaths=github.com/go-delve/delve
+	$
+
+6. Subtract one profile from another
+
+	$ go tool covdata subtract -i=indir1,indir2 -o=outdir
+	$
+
+7. Intersect profiles
+
+	$ go tool covdata intersect -i=indir1,indir2 -o=outdir
+	$
+
+8. Dump a profile for debugging purposes.
+
+	$ go tool covdata debugdump -i=indir
+	<human readable output>
+	$
+*/
 package main
diff --git a/src/cmd/go/scriptconds_test.go b/src/cmd/go/scriptconds_test.go
index 641f69f312..8dd9b0d1cd 100644
--- a/src/cmd/go/scriptconds_test.go
+++ b/src/cmd/go/scriptconds_test.go
@@ -49,6 +49,7 @@ func scriptConditions() map[string]script.Cond {
 	add("git", lazyBool("the 'git' executable exists and provides the standard CLI", hasWorkingGit))
 	add("GODEBUG", script.PrefixCondition("GODEBUG contains <suffix>", hasGodebug))
 	add("GOEXPERIMENT", script.PrefixCondition("GOEXPERIMENT <suffix> is enabled", hasGoexperiment))
+	add("go-builder", script.BoolCondition("GO_BUILDER_NAME is non-empty", testenv.Builder() != ""))
 	add("link", lazyBool("testenv.HasLink()", testenv.HasLink))
 	add("mismatched-goroot", script.Condition("test's GOROOT_FINAL does not match the real GOROOT", isMismatchedGoroot))
 	add("msan", sysCondition("-msan", platform.MSanSupported, true))
diff --git a/src/cmd/go/testdata/script/README b/src/cmd/go/testdata/script/README
index b7215e8f4f..792a158760 100644
--- a/src/cmd/go/testdata/script/README
+++ b/src/cmd/go/testdata/script/README
@@ -398,6 +398,8 @@ The available conditions are:
 	GOOS/GOARCH supports -fuzz with instrumentation
 [git]
 	the 'git' executable exists and provides the standard CLI
+[go-builder]
+	GO_BUILDER_NAME is non-empty
 [link]
 	testenv.HasLink()
 [mismatched-goroot]
diff --git a/src/cmd/go/testdata/script/gotoolchain_net.txt b/src/cmd/go/testdata/script/gotoolchain_net.txt
index 72bb2b7252..35f6696454 100644
--- a/src/cmd/go/testdata/script/gotoolchain_net.txt
+++ b/src/cmd/go/testdata/script/gotoolchain_net.txt
@@ -43,11 +43,13 @@ env GOSUMDB=$oldsumdb
 # Test a real GOTOOLCHAIN
 [short] skip
 [!net:golang.org] skip
+[!net:sum.golang.org] skip
 [!GOOS:darwin] [!GOOS:windows] [!GOOS:linux] skip
 [!GOARCH:amd64] [!GOARCH:arm64] skip
 
 env GOPROXY=
-env GOSUMDB=
+[go-builder] env GOSUMDB=
+[!go-builder] env GOSUMDB=sum.golang.org  # Set explicitly in case GOROOT/go.env is modified.
 env GOTOOLCHAIN=go1.20.1
 
 	# Avoid resolving a "go1.20.1" from the user's real $PATH.
diff --git a/src/cmd/go/testdata/script/gotoolchain_version.txt b/src/cmd/go/testdata/script/gotoolchain_version.txt
index ba1bde6671..e0736ff980 100644
--- a/src/cmd/go/testdata/script/gotoolchain_version.txt
+++ b/src/cmd/go/testdata/script/gotoolchain_version.txt
@@ -1,6 +1,15 @@
-[!net:golang.org] skip
+[!net:proxy.golang.org] skip
 
-env GOPROXY=
+	# In the Go project's official release GOPROXY defaults to proxy.golang.org,
+	# but it may be changed in GOROOT/go.env (such as in third-party
+	# distributions).
+	#
+	# Make sure it is in use here, because the server for releases not served
+	# through the proxy (https://golang.org/toolchain?go-get=1) currently only
+	# serves the latest patch release for each of the supported stable releases.
+
+[go-builder] env GOPROXY=
+[!go-builder] env GOPROXY=https://proxy.golang.org
 
 go list -m -versions go
 stdout 1.20.1 # among others
diff --git a/src/cmd/go/testdata/script/mod_prefer_compatible.txt b/src/cmd/go/testdata/script/mod_prefer_compatible.txt
index 57036b95be..4d583ff5f7 100644
--- a/src/cmd/go/testdata/script/mod_prefer_compatible.txt
+++ b/src/cmd/go/testdata/script/mod_prefer_compatible.txt
@@ -10,9 +10,9 @@ env GOPROXY=
 env GOSUMDB=
 
 # github.com/russross/blackfriday v2.0.0+incompatible exists,
-# and should be resolved if we ask for v2.0 explicitly.
+# and should be resolved if we ask for it explicitly.
 
-go list -m github.com/russross/blackfriday@v2.0
+go list -m github.com/russross/blackfriday@v2.0.0+incompatible
 stdout '^github.com/russross/blackfriday v2\.0\.0\+incompatible$'
 
 # blackfriday v1.5.2 has a go.mod file, so v1.5.2 should be preferred over
@@ -27,6 +27,7 @@ stdout '^github.com/russross/blackfriday v1\.'
 ! go list -m github.com/russross/blackfriday@patch
 stderr '^go: github.com/russross/blackfriday@patch: can''t query version "patch" of module github.com/russross/blackfriday: no existing version is required$'
 
+
 # If we're fetching directly from version control, ignored +incompatible
 # versions should also be omitted by 'go list'.
 
@@ -38,10 +39,23 @@ stderr '^go: github.com/russross/blackfriday@patch: can''t query version "patch"
 [!git] stop
 env GOPROXY=direct
 
-go list -versions -m github.com/russross/blackfriday github.com/russross/blackfriday
+go list -versions -m github.com/russross/blackfriday
 stdout '^github.com/russross/blackfriday v1\.5\.1 v1\.5\.2' # and possibly others
 ! stdout ' v2\.'
 
+# For this module, v2.1.0 exists and has a go.mod file.
+# 'go list -m github.com/russross/blackfriday@v2.0' will check
+# the latest v2.0 tag, discover that it isn't the right module, and stop there
+# (instead of spending the time to check O(N) previous tags).
+
+! go list -m github.com/russross/blackfriday@v2.0
+stderr '^go: module github.com/russross/blackfriday: no matching versions for query "v2\.0\"'
+
+# (But asking for exactly v2.0.0+incompatible should still succeed.)
+go list -m github.com/russross/blackfriday@v2.0.0+incompatible
+stdout '^github.com/russross/blackfriday v2\.0\.0\+incompatible$'
+
+
 # However, if the latest compatible version does not include a go.mod file,
 # +incompatible versions should still be listed, as they may still reflect the
 # intent of the module author.
diff --git a/src/cmd/go/testdata/script/mod_sumdb_file_path.txt b/src/cmd/go/testdata/script/mod_sumdb_file_path.txt
index c95a667bfd..2f42cb54f5 100644
--- a/src/cmd/go/testdata/script/mod_sumdb_file_path.txt
+++ b/src/cmd/go/testdata/script/mod_sumdb_file_path.txt
@@ -1,7 +1,9 @@
 [!net:proxy.golang.org] skip
+[!net:sum.golang.org] skip
 
 env GO111MODULE=on
-env GOSUMDB=
+[go-builder] env GOSUMDB=
+[!go-builder] env GOSUMDB=sum.golang.org  # Set explicitly in case GOROOT/go.env is modified.
 env GOPATH=$WORK/gopath1
 
 # With a file-based proxy with an empty checksum directory,
diff --git a/src/cmd/go/testdata/script/mod_sumdb_golang.txt b/src/cmd/go/testdata/script/mod_sumdb_golang.txt
index 8698412f78..067e2e3b31 100644
--- a/src/cmd/go/testdata/script/mod_sumdb_golang.txt
+++ b/src/cmd/go/testdata/script/mod_sumdb_golang.txt
@@ -1,13 +1,13 @@
 # Test default GOPROXY and GOSUMDB
-env GOPROXY=
-env GOSUMDB=
-go env GOPROXY
-stdout '^https://proxy.golang.org,direct$'
-go env GOSUMDB
-stdout '^sum.golang.org$'
-env GOPROXY=https://proxy.golang.org
-go env GOSUMDB
-stdout '^sum.golang.org$'
+[go-builder] env GOPROXY=
+[go-builder] env GOSUMDB=
+[go-builder] go env GOPROXY
+[go-builder] stdout '^https://proxy.golang.org,direct$'
+[go-builder] go env GOSUMDB
+[go-builder] stdout '^sum.golang.org$'
+[go-builder] env GOPROXY=https://proxy.golang.org
+[go-builder] go env GOSUMDB
+[go-builder] stdout '^sum.golang.org$'
 
 # Download direct from github.
 
@@ -26,8 +26,8 @@ cp go.sum saved.sum
 # files not listed in go.sum.
 
 go clean -modcache
-env GOSUMDB=
-env GOPROXY=
+env GOSUMDB=sum.golang.org
+env GOPROXY=https://proxy.golang.org,direct
 
 go list -x -m all  # Download go.mod files.
 ! stderr github
diff --git a/src/go/types/const.go b/src/go/types/const.go
index 66fa60804f..bffea146a0 100644
--- a/src/go/types/const.go
+++ b/src/go/types/const.go
@@ -74,7 +74,6 @@ func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *c
 
 	sizeof := func(T Type) int64 {
 		s := conf.sizeof(T)
-		assert(s == 4 || s == 8)
 		return s
 	}
 
diff --git a/src/log/slog/handler.go b/src/log/slog/handler.go
index e479ca8a4c..a73983cda3 100644
--- a/src/log/slog/handler.go
+++ b/src/log/slog/handler.go
@@ -193,7 +193,7 @@ type commonHandler struct {
 	groupPrefix string
 	groups      []string // all groups started from WithGroup
 	nOpenGroups int      // the number of groups opened in preformattedAttrs
-	mu          sync.Mutex
+	mu          *sync.Mutex
 	w           io.Writer
 }
 
@@ -207,6 +207,7 @@ func (h *commonHandler) clone() *commonHandler {
 		groups:            slices.Clip(h.groups),
 		nOpenGroups:       h.nOpenGroups,
 		w:                 h.w,
+		mu:                h.mu, // mutex shared among all clones of this handler
 	}
 }
 
@@ -252,6 +253,8 @@ func (h *commonHandler) withGroup(name string) *commonHandler {
 	return h2
 }
 
+// handle is the internal implementation of Handler.Handle
+// used by TextHandler and JSONHandler.
 func (h *commonHandler) handle(r Record) error {
 	state := h.newHandleState(buffer.New(), true, "")
 	defer state.free()
diff --git a/src/log/slog/handler_test.go b/src/log/slog/handler_test.go
index 3fb7360fc2..4f10ee5028 100644
--- a/src/log/slog/handler_test.go
+++ b/src/log/slog/handler_test.go
@@ -16,6 +16,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -106,6 +107,52 @@ func TestDefaultHandle(t *testing.T) {
 	}
 }
 
+func TestConcurrentWrites(t *testing.T) {
+	ctx := context.Background()
+	count := 1000
+	for _, handlerType := range []string{"text", "json"} {
+		t.Run(handlerType, func(t *testing.T) {
+			var buf bytes.Buffer
+			var h Handler
+			switch handlerType {
+			case "text":
+				h = NewTextHandler(&buf, nil)
+			case "json":
+				h = NewJSONHandler(&buf, nil)
+			default:
+				t.Fatalf("unexpected handlerType %q", handlerType)
+			}
+			sub1 := h.WithAttrs([]Attr{Bool("sub1", true)})
+			sub2 := h.WithAttrs([]Attr{Bool("sub2", true)})
+			var wg sync.WaitGroup
+			for i := 0; i < count; i++ {
+				sub1Record := NewRecord(time.Time{}, LevelInfo, "hello from sub1", 0)
+				sub1Record.AddAttrs(Int("i", i))
+				sub2Record := NewRecord(time.Time{}, LevelInfo, "hello from sub2", 0)
+				sub2Record.AddAttrs(Int("i", i))
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					if err := sub1.Handle(ctx, sub1Record); err != nil {
+						t.Error(err)
+					}
+					if err := sub2.Handle(ctx, sub2Record); err != nil {
+						t.Error(err)
+					}
+				}()
+			}
+			wg.Wait()
+			for i := 1; i <= 2; i++ {
+				want := "hello from sub" + strconv.Itoa(i)
+				n := strings.Count(buf.String(), want)
+				if n != count {
+					t.Fatalf("want %d occurrences of %q, got %d", count, want, n)
+				}
+			}
+		})
+	}
+}
+
 // Verify the common parts of TextHandler and JSONHandler.
 func TestJSONAndTextHandlers(t *testing.T) {
 	// remove all Attrs
diff --git a/src/log/slog/json_handler.go b/src/log/slog/json_handler.go
index cebcfba45a..1c51ab05ff 100644
--- a/src/log/slog/json_handler.go
+++ b/src/log/slog/json_handler.go
@@ -13,6 +13,7 @@ import (
 	"io"
 	"log/slog/internal/buffer"
 	"strconv"
+	"sync"
 	"time"
 	"unicode/utf8"
 )
@@ -35,6 +36,7 @@ func NewJSONHandler(w io.Writer, opts *HandlerOptions) *JSONHandler {
 			json: true,
 			w:    w,
 			opts: *opts,
+			mu:   &sync.Mutex{},
 		},
 	}
 }
diff --git a/src/log/slog/text_handler.go b/src/log/slog/text_handler.go
index 75b66b716f..58edb2f66d 100644
--- a/src/log/slog/text_handler.go
+++ b/src/log/slog/text_handler.go
@@ -11,6 +11,7 @@ import (
 	"io"
 	"reflect"
 	"strconv"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 )
@@ -33,6 +34,7 @@ func NewTextHandler(w io.Writer, opts *HandlerOptions) *TextHandler {
 			json: false,
 			w:    w,
 			opts: *opts,
+			mu:   &sync.Mutex{},
 		},
 	}
 }
diff --git a/src/math/huge_test.go b/src/math/huge_test.go
index bc28c6ff69..568b0c85eb 100644
--- a/src/math/huge_test.go
+++ b/src/math/huge_test.go
@@ -81,6 +81,10 @@ func TestHugeCos(t *testing.T) {
 		if !close(f1, f2) {
 			t.Errorf("Cos(%g) = %g, want %g", trigHuge[i], f2, f1)
 		}
+		f3 := Cos(-trigHuge[i])
+		if !close(f1, f3) {
+			t.Errorf("Cos(%g) = %g, want %g", -trigHuge[i], f3, f1)
+		}
 	}
 }
 
@@ -91,6 +95,10 @@ func TestHugeSin(t *testing.T) {
 		if !close(f1, f2) {
 			t.Errorf("Sin(%g) = %g, want %g", trigHuge[i], f2, f1)
 		}
+		f3 := Sin(-trigHuge[i])
+		if !close(-f1, f3) {
+			t.Errorf("Sin(%g) = %g, want %g", -trigHuge[i], f3, -f1)
+		}
 	}
 }
 
@@ -101,6 +109,10 @@ func TestHugeSinCos(t *testing.T) {
 		if !close(f1, f2) || !close(g1, g2) {
 			t.Errorf("Sincos(%g) = %g, %g, want %g, %g", trigHuge[i], f2, g2, f1, g1)
 		}
+		f3, g3 := Sincos(-trigHuge[i])
+		if !close(-f1, f3) || !close(g1, g3) {
+			t.Errorf("Sincos(%g) = %g, %g, want %g, %g", -trigHuge[i], f3, g3, -f1, g1)
+		}
 	}
 }
 
@@ -111,5 +123,9 @@ func TestHugeTan(t *testing.T) {
 		if !close(f1, f2) {
 			t.Errorf("Tan(%g) = %g, want %g", trigHuge[i], f2, f1)
 		}
+		f3 := Tan(-trigHuge[i])
+		if !close(-f1, f3) {
+			t.Errorf("Tan(%g) = %g, want %g", -trigHuge[i], f3, -f1)
+		}
 	}
 }
diff --git a/src/net/rpc/server.go b/src/net/rpc/server.go
index 109ebba541..5cea2cc507 100644
--- a/src/net/rpc/server.go
+++ b/src/net/rpc/server.go
@@ -86,9 +86,9 @@ The server calls (for HTTP service):
 	arith := new(Arith)
 	rpc.Register(arith)
 	rpc.HandleHTTP()
-	l, e := net.Listen("tcp", ":1234")
-	if e != nil {
-		log.Fatal("listen error:", e)
+	l, err := net.Listen("tcp", ":1234")
+	if err != nil {
+		log.Fatal("listen error:", err)
 	}
 	go http.Serve(l, nil)
 
diff --git a/src/net/rpc/server_test.go b/src/net/rpc/server_test.go
index dc5f5decc7..6a94d6ebe8 100644
--- a/src/net/rpc/server_test.go
+++ b/src/net/rpc/server_test.go
@@ -110,9 +110,9 @@ func (BuiltinTypes) Array(args *Args, reply *[2]int) error {
 }
 
 func listenTCP() (net.Listener, string) {
-	l, e := net.Listen("tcp", "127.0.0.1:0") // any available address
-	if e != nil {
-		log.Fatalf("net.Listen tcp :0: %v", e)
+	l, err := net.Listen("tcp", "127.0.0.1:0") // any available address
+	if err != nil {
+		log.Fatalf("net.Listen tcp :0: %v", err)
 	}
 	return l, l.Addr().String()
 }