cmd/go: enable GOCACHEPROG by default, without GOEXPERIMENT

Fixes #64876

Change-Id: I2c0e1ed22f8e13d00dfb5fededbc84038cd7ff8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/626035
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Sam Thanawalla <samthanawalla@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>

doc/next/3-tools.md

@@ -20,3 +20,11 @@ non-existent identifiers. Some of these mistakes may cause tests not
 to run.
 
 This analyzer is among the subset of analyzers that are run by `go test`.
+
+### GOCACHEPROG
+
+The `cmd/go` internal binary and test caching mechanism can now be implemented
+by child processes implementing a JSON protocol between the `cmd/go` tool
+and the child process named by the `GOCACHEPROG` environment variable.
+This was previously behind a GOEXPERIMENT.
+For protocol details, see [#59719](/issue/59719).

src/cmd/go/internal/cache/default.go

@@ -12,7 +12,6 @@ import (
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
-	"internal/goexperiment"
 )
 
 // Default returns the default cache to use.
@@ -55,7 +54,7 @@ func initDefaultCache() Cache {
 		base.Fatalf("failed to initialize build cache at %s: %s\n", dir, err)
 	}
 
-	if v := cfg.Getenv("GOCACHEPROG"); v != "" && goexperiment.CacheProg {
+	if v := cfg.Getenv("GOCACHEPROG"); v != "" {
 		return startCacheProg(v, diskCache)
 	}
 

src/cmd/go/internal/cache/prog.go

@@ -14,6 +14,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"internal/goexperiment"
 	"io"
 	"log"
 	"os"
@@ -91,8 +92,11 @@ type ProgRequest struct {
 	// ActionID is non-nil for get and puts.
 	ActionID []byte `json:",omitempty"` // or nil if not used
 
-	// ObjectID is set for Type "put" and "output-file".
+	// OutputID is set for Type "put".
-	ObjectID []byte `json:",omitempty"` // or nil if not used
+	//
+	// Prior to Go 1.24, when GOCACHEPROG was still an experiment, this was
+	// accidentally named ObjectID. It was renamed to OutputID in Go 1.24.
+	OutputID []byte `json:",omitempty"` // or nil if not used
 
 	// Body is the body for "put" requests. It's sent after the JSON object
 	// as a base64-encoded JSON string when BodySize is non-zero.
@@ -104,6 +108,14 @@ type ProgRequest struct {
 
 	// BodySize is the number of bytes of Body. If zero, the body isn't written.
 	BodySize int64 `json:",omitempty"`
+
+	// ObjectID is the accidental spelling of OutputID that was used prior to Go
+	// 1.24.
+	//
+	// Deprecated: use OutputID. This field is only populated temporarily for
+	// backwards compatibility with Go 1.23 and earlier when
+	// GOEXPERIMENT=gocacheprog is set. It will be removed in Go 1.25.
+	ObjectID []byte `json:",omitempty"`
 }
 
 // ProgResponse is the JSON response from the child process to cmd/go.
@@ -302,8 +314,8 @@ func (c *ProgCache) writeToChild(req *ProgRequest, resc chan<- *ProgResponse) (e
 			return nil
 		}
 		if wrote != req.BodySize {
-			return fmt.Errorf("short write writing body to GOCACHEPROG for action %x, object %x: wrote %v; expected %v",
+			return fmt.Errorf("short write writing body to GOCACHEPROG for action %x, output %x: wrote %v; expected %v",
-				req.ActionID, req.ObjectID, wrote, req.BodySize)
+				req.ActionID, req.OutputID, wrote, req.BodySize)
 		}
 		if _, err := c.bw.WriteString("\"\n"); err != nil {
 			return err
@@ -388,10 +400,18 @@ func (c *ProgCache) Put(a ActionID, file io.ReadSeeker) (_ OutputID, size int64,
 		return out, size, nil
 	}
 
+	// For compatibility with Go 1.23/1.24 GOEXPERIMENT=gocacheprog users, also
+	// populate the deprecated ObjectID field. This will be removed in Go 1.25.
+	var deprecatedValue []byte
+	if goexperiment.CacheProg {
+		deprecatedValue = out[:]
+	}
+
 	res, err := c.send(c.ctx, &ProgRequest{
 		Command:  cmdPut,
 		ActionID: a[:],
-		ObjectID: out[:],
+		OutputID: out[:],
+		ObjectID: deprecatedValue, // TODO(bradfitz): remove in Go 1.25
 		Body:     file,
 		BodySize: size,
 	})