cmd/go: introduce GOROOT/go.env and move proxy/sumdb config there

Various Linux distributions edit cmd/go/internal/cfg/cfg.go to change
the default settings of GOPROXY and GOSUMDB. Make it possible for
them to do this without editing the go command source code by
introducing GOROOT/go.env and moving those defaults there.

With the upcoming changes for reproducible builds (#24904),
this should mean that Linux distributions distribute binaries
that are bit-for-bit identical to the Go distribution binaries,
even when rebuilding the distribution themselves.

Fixes #57179.

Change-Id: Ib2ecc61e6d036f97db6fd47dca757c94fdea5629
Reviewed-on: https://go-review.googlesource.com/c/go/+/462198
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

diff --git a/go.env b/go.env
new file mode 100644 (file)
index 0000000..8261922
--- /dev/null
+++ b/go.env
@@ -0,0 +1,8 @@
+# This file contains the initial defaults for go command configuration.
+# Values set by 'go env -w' and written to the user's go/env file override these.
+# The environment overrides everything else.
+
+# Use the Go module mirror and checksum database by default.
+# See https://proxy.golang.org for details.
+GOPROXY=https://proxy.golang.org,direct
+GOSUMDB=sum.golang.org

diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 3257140515030b593b5b1f0e57c1dd724ded9a72..563335220b69cd347fb8e027672b7cb2737560ac 100644 (file)
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -179,7 +179,7 @@ func defaultContext() build.Context {
 }
 
 func init() {
-       SetGOROOT(findGOROOT(), false)
+       SetGOROOT(Getenv("GOROOT"), false)
        BuildToolchainCompiler = func() string { return "missing-compiler" }
        BuildToolchainLinker = func() string { return "missing-linker" }
 }
@@ -303,7 +303,22 @@ func EnvFile() (string, error) {
 
 func initEnvCache() {
        envCache.m = make(map[string]string)
-       file, _ := EnvFile()
+       if file, _ := EnvFile(); file != "" {
+               readEnvFile(file, "user")
+       }
+       goroot := findGOROOT(envCache.m["GOROOT"])
+       if goroot != "" {
+               readEnvFile(filepath.Join(goroot, "go.env"), "GOROOT")
+       }
+
+       // Save the goroot for func init calling SetGOROOT,
+       // and also overwrite anything that might have been in go.env.
+       // It makes no sense for GOROOT/go.env to specify
+       // a different GOROOT.
+       envCache.m["GOROOT"] = goroot
+}
+
+func readEnvFile(file string, source string) {
        if file == "" {
                return
        }
@@ -325,13 +340,21 @@ func initEnvCache() {
                i = bytes.IndexByte(line, '=')
                if i < 0 || line[0] < 'A' || 'Z' < line[0] {
                        // Line is missing = (or empty) or a comment or not a valid env name. Ignore.
-                       // (This should not happen, since the file should be maintained almost
+                       // This should not happen in the user file, since the file should be maintained almost
                        // exclusively by "go env -w", but better to silently ignore than to make
                        // the go command unusable just because somehow the env file has
-                       // gotten corrupted.)
+                       // gotten corrupted.
+                       // In the GOROOT/go.env file, we expect comments.
                        continue
                }
                key, val := line[:i], line[i+1:]
+
+               if source == "GOROOT" {
+                       // In the GOROOT/go.env file, do not overwrite fields loaded from the user's go/env file.
+                       if _, ok := envCache.m[string(key)]; ok {
+                               continue
+                       }
+               }
                envCache.m[string(key)] = string(val)
        }
 }
@@ -383,8 +406,8 @@ var (
        GOPPC64  = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", buildcfg.GOPPC64))
        GOWASM   = envOr("GOWASM", fmt.Sprint(buildcfg.GOWASM))
 
-       GOPROXY    = envOr("GOPROXY", "https://proxy.golang.org,direct")
-       GOSUMDB    = envOr("GOSUMDB", "sum.golang.org")
+       GOPROXY    = envOr("GOPROXY", "")
+       GOSUMDB    = envOr("GOSUMDB", "")
        GOPRIVATE  = Getenv("GOPRIVATE")
        GONOPROXY  = envOr("GONOPROXY", GOPRIVATE)
        GONOSUMDB  = envOr("GONOSUMDB", GOPRIVATE)
@@ -437,8 +460,14 @@ func envOr(key, def string) string {
 // with from runtime.GOROOT().
 //
 // There is a copy of this code in x/tools/cmd/godoc/goroot.go.
-func findGOROOT() string {
-       if env := Getenv("GOROOT"); env != "" {
+func findGOROOT(env string) string {
+       if env == "" {
+               // Not using Getenv because findGOROOT is called
+               // to find the GOROOT/go.env file. initEnvCache
+               // has passed in the setting from the user go/env file.
+               env = os.Getenv("GOROOT")
+       }
+       if env != "" {
                return filepath.Clean(env)
        }
        def := ""