Revert "testing: add TB.SetGOMAXPROCS function"

This reverts CL 519235.

Reason for revert: Proposal is still in incoming.

For #62020

Change-Id: Icccb930209f36097f5d930c01eda6b5042bdddc1
Reviewed-on: https://go-review.googlesource.com/c/go/+/573516
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

api/next/62020.txt

@@ -1,4 +0,0 @@
-pkg testing, type TB interface, SetGOMAXPROCS(int) #62020
-pkg testing, method (*T) SetGOMAXPROCS(int) #62020
-pkg testing, method (*B) SetGOMAXPROCS(int) #62020
-pkg testing, method (*F) SetGOMAXPROCS(int) #62020

doc/next/6-stdlib/99-minor/testing/62020.md

@@ -1 +0,0 @@
-The [`SetGOMAXPROCS`](/pkg/testing#T.SetGOMAXPROCS) method changes GOMAXPROCS for the duration of a single test.

src/testing/testing.go

@@ -890,7 +890,6 @@ type TB interface {
 	Logf(format string, args ...any)
 	Name() string
 	Setenv(key, value string)
-	SetGOMAXPROCS(n int)
 	Skip(args ...any)
 	SkipNow()
 	Skipf(format string, args ...any)
@@ -917,9 +916,8 @@ var _ TB = (*B)(nil)
 // may be called simultaneously from multiple goroutines.
 type T struct {
 	common
-	isEnvSet        bool
+	isEnvSet bool
-	isGOMAXPROCSSet bool
+	context  *testContext // For running tests and subtests.
-	context         *testContext // For running tests and subtests.
 }
 
 func (c *common) private() {}
@@ -1308,19 +1306,6 @@ func (c *common) Setenv(key, value string) {
 	}
 }
 
-// SetGOMAXPROCS calls runtime.GOMAXPROCS(n) and uses Cleanup to
-// restore the value of GOMAXPROCS after the test.
-//
-// Because GOMAXPROCS affects the whole process, it cannot be used
-// in parallel tests or tests with parallel ancestors.
-func (c *common) SetGOMAXPROCS(n int) {
-	c.checkFuzzFn("SetGOMAXPROCS")
-	prev := runtime.GOMAXPROCS(n)
-	c.Cleanup(func() {
-		runtime.GOMAXPROCS(prev)
-	})
-}
-
 // panicHanding controls the panic handling used by runCleanup.
 type panicHandling int
 
@@ -1461,9 +1446,6 @@ func (t *T) Parallel() {
 	if t.isEnvSet {
 		panic("testing: t.Parallel called after t.Setenv; cannot set environment variables in parallel tests")
 	}
-	if t.isGOMAXPROCSSet {
-		panic("testing: t.Parallel called after t.SetGOMAXPROCS; cannot set GOMAXPROCS in parallel tests")
-	}
 	t.isParallel = true
 	if t.parent.barrier == nil {
 		// T.Parallel has no effect when fuzzing.
@@ -1545,33 +1527,6 @@ func (t *T) Setenv(key, value string) {
 	t.common.Setenv(key, value)
 }
 
-// SetGOMAXPROCS calls runtime.GOMAXPROCS(n) and uses Cleanup to
-// restore the value of GOMAXPROCS after the test.
-//
-// Because GOMAXPROCS affects the whole process, it cannot be used
-// in parallel tests or tests with parallel ancestors.
-func (t *T) SetGOMAXPROCS(n int) {
-	// Non-parallel subtests that have parallel ancestors may still
-	// run in parallel with other tests: they are only non-parallel
-	// with respect to the other subtests of the same parent.
-	// Since SetGOMAXPROCS affects the whole process, we need to disallow it
-	// if the current test or any parent is parallel.
-	isParallel := false
-	for c := &t.common; c != nil; c = c.parent {
-		if c.isParallel {
-			isParallel = true
-			break
-		}
-	}
-	if isParallel {
-		panic("testing: t.SetGOMAXPROCS called after t.Parallel; cannot set GOMAXPROCS in parallel tests")
-	}
-
-	t.isGOMAXPROCSSet = true
-
-	t.common.SetGOMAXPROCS(n)
-}
-
 // InternalTest is an internal type but exported because it is cross-package;
 // it is part of the implementation of the "go test" command.
 type InternalTest struct {

src/testing/testing_test.go

@@ -13,7 +13,6 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
-	"runtime"
 	"slices"
 	"strings"
 	"sync"
@@ -259,102 +258,6 @@ func TestSetenvWithParallelGrandParentBeforeSetenv(t *testing.T) {
 	})
 }
 
-func TestSetGOMAXPROCS(t *testing.T) {
-	if runtime.GOARCH == "wasm" {
-		t.Skip("not supported on wasm yet")
-	}
-	tests := []struct {
-		name string
-		newP int
-	}{
-		{
-			name: "overriding value",
-			newP: 1,
-		},
-	}
-
-	for _, test := range tests {
-		p := runtime.GOMAXPROCS(0)
-		t.Run(test.name, func(t *testing.T) {
-			t.SetGOMAXPROCS(test.newP + 1)
-			if runtime.GOMAXPROCS(0) != test.newP+1 {
-				t.Fatalf("unexpected value after t.SetGOMAXPROCS: got %d, want %d", runtime.GOMAXPROCS(0), test.newP+1)
-			}
-		})
-		if runtime.GOMAXPROCS(0) != p {
-			t.Fatalf("unexpected value after t.SetGOMAXPROCS cleanup: got %d, want %d", runtime.GOMAXPROCS(0), p)
-		}
-	}
-}
-
-func TestSetGOMAXPROCSWithParallelAfterSetGOMAXPROCS(t *testing.T) {
-	if runtime.GOARCH == "wasm" {
-		t.Skip("not supported on wasm yet")
-	}
-	defer func() {
-		want := "testing: t.Parallel called after t.SetGOMAXPROCS; cannot set GOMAXPROCS in parallel tests"
-		if got := recover(); got != want {
-			t.Fatalf("expected panic; got %#v want %q", got, want)
-		}
-	}()
-	p := runtime.GOMAXPROCS(0)
-	t.SetGOMAXPROCS(p + 1)
-	t.Parallel()
-}
-
-func TestSetGOMAXPROCSWithParallelBeforeSetGOMAXPROCS(t *testing.T) {
-	if runtime.GOARCH == "wasm" {
-		t.Skip("not supported on wasm yet")
-	}
-	defer func() {
-		want := "testing: t.SetGOMAXPROCS called after t.Parallel; cannot set GOMAXPROCS in parallel tests"
-		if got := recover(); got != want {
-			t.Fatalf("expected panic; got %#v want %q", got, want)
-		}
-	}()
-	t.Parallel()
-	p := runtime.GOMAXPROCS(0)
-	t.SetGOMAXPROCS(p + 1)
-}
-
-func TestSetGOMAXPROCSWithParallelParentBeforeSetGOMAXPROCS(t *testing.T) {
-	if runtime.GOARCH == "wasm" {
-		t.Skip("not supported on wasm yet")
-	}
-	t.Parallel()
-	t.Run("child", func(t *testing.T) {
-		defer func() {
-			want := "testing: t.SetGOMAXPROCS called after t.Parallel; cannot set GOMAXPROCS in parallel tests"
-			if got := recover(); got != want {
-				t.Fatalf("expected panic; got %#v want %q", got, want)
-			}
-		}()
-
-		p := runtime.GOMAXPROCS(0)
-		t.SetGOMAXPROCS(p + 1)
-	})
-}
-
-func TestSetGOMAXPROCSWithParallelGrandParentBeforeSetGOMAXPROCS(t *testing.T) {
-	if runtime.GOARCH == "wasm" {
-		t.Skip("not supported on wasm yet")
-	}
-	t.Parallel()
-	t.Run("child", func(t *testing.T) {
-		t.Run("grand-child", func(t *testing.T) {
-			defer func() {
-				want := "testing: t.SetGOMAXPROCS called after t.Parallel; cannot set GOMAXPROCS in parallel tests"
-				if got := recover(); got != want {
-					t.Fatalf("expected panic; got %#v want %q", got, want)
-				}
-			}()
-
-			p := runtime.GOMAXPROCS(0)
-			t.SetGOMAXPROCS(p + 1)
-		})
-	})
-}
-
 // testingTrueInInit is part of TestTesting.
 var testingTrueInInit = false