1 files changed, 108 insertions, 0 deletions
diff --git a/src/cmd/go/internal/gover/toolchain.go b/src/cmd/go/internal/gover/toolchain.go
new file mode 100644
index 0000000..43b117e
--- /dev/null
+++ b/src/cmd/go/internal/gover/toolchain.go
@@ -0,0 +1,108 @@
+// Copyright 2023 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 gover
+
+import (
+	"cmd/go/internal/base"
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// FromToolchain returns the Go version for the named toolchain,
+// derived from the name itself (not by running the toolchain).
+// A toolchain is named "goVERSION".
+// A suffix after the VERSION introduced by a -, space, or tab is removed.
+// Examples:
+//
+//	FromToolchain("go1.2.3") == "1.2.3"
+//	FromToolchain("go1.2.3-bigcorp") == "1.2.3"
+//	FromToolchain("invalid") == ""
+func FromToolchain(name string) string {
+	if strings.ContainsAny(name, "\\/") {
+		// The suffix must not include a path separator, since that would cause
+		// exec.LookPath to resolve it from a relative directory instead of from
+		// $PATH.
+		return ""
+	}
+
+	var v string
+	if strings.HasPrefix(name, "go") {
+		v = name[2:]
+	} else {
+		return ""
+	}
+	// Some builds use custom suffixes; strip them.
+	if i := strings.IndexAny(v, " \t-"); i >= 0 {
+		v = v[:i]
+	}
+	if !IsValid(v) {
+		return ""
+	}
+	return v
+}
+
+func maybeToolchainVersion(name string) string {
+	if IsValid(name) {
+		return name
+	}
+	return FromToolchain(name)
+}
+
+// ToolchainMax returns the maximum of x and y interpreted as toolchain names,
+// compared using Compare(FromToolchain(x), FromToolchain(y)).
+// If x and y compare equal, Max returns x.
+func ToolchainMax(x, y string) string {
+	if Compare(FromToolchain(x), FromToolchain(y)) < 0 {
+		return y
+	}
+	return x
+}
+
+// Startup records the information that went into the startup-time version switch.
+// It is initialized by switchGoToolchain.
+var Startup struct {
+	GOTOOLCHAIN   string // $GOTOOLCHAIN setting
+	AutoFile      string // go.mod or go.work file consulted
+	AutoGoVersion string // go line found in file
+	AutoToolchain string // toolchain line found in file
+}
+
+// A TooNewError explains that a module is too new for this version of Go.
+type TooNewError struct {
+	What      string
+	GoVersion string
+	Toolchain string // for callers if they want to use it, but not printed
+}
+
+func (e *TooNewError) Error() string {
+	var explain string
+	if Startup.GOTOOLCHAIN != "" && Startup.GOTOOLCHAIN != "auto" {
+		explain = "; GOTOOLCHAIN=" + Startup.GOTOOLCHAIN
+	}
+	if Startup.AutoFile != "" && (Startup.AutoGoVersion != "" || Startup.AutoToolchain != "") {
+		explain += fmt.Sprintf("; %s sets ", base.ShortPath(Startup.AutoFile))
+		if Startup.AutoToolchain != "" {
+			explain += "toolchain " + Startup.AutoToolchain
+		} else {
+			explain += "go " + Startup.AutoGoVersion
+		}
+	}
+	return fmt.Sprintf("%v requires go >= %v (running go %v%v)", e.What, e.GoVersion, Local(), explain)
+}
+
+var ErrTooNew = errors.New("module too new")
+
+func (e *TooNewError) Is(err error) bool {
+	return err == ErrTooNew
+}
+
+// A Switcher provides the ability to switch to a new toolchain in response to TooNewErrors.
+// See [cmd/go/internal/toolchain.Switcher] for documentation.
+type Switcher interface {
+	Error(err error)
+	Switch(ctx context.Context)
+}