nogo: set std language version from std go.mod

This change is a no-op, as we already used the toolchain language
version.

PiperOrigin-RevId: 926779620

tools/bazeldefs/go.bzl

@@ -182,6 +182,11 @@ def go_context(ctx, goos = None, goarch = None):
     if go_ctx.mode.msan:
         nogo_args = nogo_args + ["-msan"]
 
+    stdlib_mods = [f for f in go_ctx.sdk.srcs.to_list() if f.path.endswith("/src/go.mod")]
+    if len(stdlib_mods) != 1:
+        fail("expect exactly one stdlib src/go.mod in %s, found %s" % (go_ctx.sdk.srcs, stdlib_mods))
+    stdlib_mod = stdlib_mods[0]
+
     return struct(
         env = dict(go_ctx.env, CGO_ENABLED = "0"),
         go = go_ctx.go,
@@ -192,6 +197,7 @@ def go_context(ctx, goos = None, goarch = None):
         nogo_args = nogo_args,
         runfiles = depset([go_ctx.go] + go_ctx.sdk.srcs.to_list() + go_ctx.sdk.tools.to_list() + go_ctx.stdlib.libs.to_list()),
         stdlib_srcs = go_ctx.sdk.srcs,
+        stdlib_mod = stdlib_mod,
     )
 
 def select_goarch():

tools/nogo/cli/cli.go

@@ -18,6 +18,7 @@ package cli
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"go/format"
 	"io"
@@ -512,6 +513,32 @@ func (r *Render) Execute(ctx context.Context, fs *flag.FlagSet, args ...any) sub
 	return subcommands.ExitSuccess
 }
 
+// goVersionRe matches a `go VERSION` line in go.mod, capturing VERSION.
+var goVersionRe = regexp.MustCompile(`^go\s+(\S+)`)
+
+// resolveGOVERSION sets flags.GOVERSION from flags.GOVERSIONModFile, if necessary.
+func resolveGOVERSION() error {
+	if flags.GOVERSIONModFile == "" {
+		// Nothing to do.
+		return nil
+	}
+	if flags.GOVERSION != "" {
+		return errors.New("only one of -GOVERSION or -GOVERSION-mod-file may be set")
+	}
+
+	b, err := os.ReadFile(flags.GOVERSIONModFile)
+	if err != nil {
+		return err
+	}
+
+	m := goVersionRe.FindStringSubmatch(string(b))
+	if len(m) != 2 {
+		return fmt.Errorf("go line not found in go.mod:\n%s", string(b))
+	}
+	flags.GOVERSION = m[1]
+	return nil
+}
+
 // Main is the main entrypoint.
 func Main() {
 	subcommands.Register(&Check{}, "")
@@ -521,5 +548,8 @@ func Main() {
 	subcommands.Register(subcommands.HelpCommand(), "")
 	subcommands.Register(subcommands.FlagsCommand(), "")
 	flag.CommandLine.Parse(os.Args[1:])
+	if err := resolveGOVERSION(); err != nil {
+		failure("error resolving GOVERSION: %v", err)
+	}
 	os.Exit(int(subcommands.Execute(context.Background())))
 }

tools/nogo/defs.bzl

@@ -69,6 +69,9 @@ def _nogo_stdlib_impl(ctx):
     # Build the configuration for the stdlib.
     go_ctx, args, inputs, raw_findings = _nogo_config(ctx, deps = [])
 
+    # GOVERSION of std is set by the std go.mod.
+    args.append("-GOVERSION-mod-file=%s" % go_ctx.stdlib_mod)
+
     # Build the analyzer command.
     facts_file = ctx.actions.declare_file(ctx.label.name + ".facts")
     findings_file = ctx.actions.declare_file(ctx.label.name + ".raw_findings")
@@ -170,7 +173,6 @@ def _nogo_config(ctx, deps):
         "-go=%s" % go_ctx.go.path,
         "-GOOS=%s" % go_ctx.goos,
         "-GOARCH=%s" % go_ctx.goarch,
-        "-GOVERSION=%s" % go_ctx.lang_version,
         "-tags=%s" % (",".join(go_ctx.gotags)),
     ]
     inputs = []
@@ -214,6 +216,9 @@ def _nogo_package_config(ctx, deps, importpath = None, target = None):
     # Returns (go_ctx, args, inputs, raw_findings).
     go_ctx, args, inputs, raw_findings = _nogo_config(ctx, deps)
 
+    # GOVERSION of packages are set by the project language version.
+    args.append("-GOVERSION=%s" % go_ctx.lang_version)
+
     # Add the module itself, for the type sanity check. This applies only to
     # the libraries, and not binaries or tests.
     binaries = []

tools/nogo/flags/flags.go

@@ -41,6 +41,12 @@ var (
 	// GOVERSION defines the Go version for analysis.
 	GOVERSION string
 
+	// GOVERSIONModFile is the path to a go.mod to extract the Go version from.
+	//
+	// Only one of GOVERSION or GOVERSIONModFile may be set. cli.Main will
+	// set GOVERSION from this mod file.
+	GOVERSIONModFile string
+
 	// BuildTags defines the set of build tags for analysis. Note that
 	// while this may also be a StringList, it is kept as an explicit
 	// comma-separated list in order to build the standard flag.
@@ -71,6 +77,7 @@ func init() {
 	flag.StringVar(&GOOS, "GOOS", runtime.GOOS, "GOOS for analysis")
 	flag.StringVar(&GOARCH, "GOARCH", runtime.GOARCH, "GOARCH for analysis")
 	flag.StringVar(&GOVERSION, "GOVERSION", "", "GOVERSION for analysis")
+	flag.StringVar(&GOVERSIONModFile, "GOVERSION-mod-file", "", "Path to go.mod containing the GOVERSION for analysis")
 	flag.StringVar(&BuildTags, "tags", "", "comma-separated build tags")
 	flag.BoolVar(&Race, "race", false, "-race build")
 	flag.BoolVar(&MSAN, "msan", false, "-msan build")