internal/lsp/cache: set types.Config.GoVersion

Set the language version from the controlling go.mod file's go version,
if any. Also verify that we properly surface a diagnostic if the version
is invalid.

I didn't add any quick fixes.

Fixes golang/go#50688.

Change-Id: Ic472502d1224a1decb5b989d51110b837020e998
Reviewed-on: https://go-review.googlesource.com/c/tools/+/383394
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

gopls/internal/regtest/diagnostics/diagnostics_test.go

@@ -2138,3 +2138,22 @@ func main() {
 		)
 	})
 }
+
+func TestLangVersion(t *testing.T) {
+	testenv.NeedsGo1Point(t, 18) // Requires types.Config.GoVersion, new in 1.18.
+	const files = `
+-- go.mod --
+module mod.com
+
+go 1.12
+-- main.go --
+package main
+
+const C = 0b10
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.Await(env.DiagnosticAtRegexpWithMessage("main.go", `0b10`, "go1.13 or later"))
+		env.WriteWorkspaceFile("go.mod", "module mod.com \n\ngo 1.13\n")
+		env.Await(EmptyDiagnostics("main.go"))
+	})
+}

gopls/internal/regtest/modfile/modfile_test.go

@@ -1120,3 +1120,20 @@ func main() {
 		)
 	})
 }
+
+func TestInvalidGoVersion(t *testing.T) {
+	testenv.NeedsGo1Point(t, 14) // Times out on 1.13 for reasons unclear. Not worth worrying about.
+	const files = `
+-- go.mod --
+module mod.com
+
+go foo
+-- main.go --
+package main
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.Await(env.DiagnosticAtRegexpWithMessage("go.mod", `go foo`, "invalid go version"))
+		env.WriteWorkspaceFile("go.mod", "module mod.com \n\ngo 1.12\n")
+		env.Await(EmptyDiagnostics("go.mod"))
+	})
+}

internal/lsp/cache/check.go

@@ -12,6 +12,7 @@ import (
 	"go/types"
 	"path"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strings"
 	"sync"
@@ -420,6 +421,8 @@ func typeCheck(ctx context.Context, snapshot *snapshot, m *Metadata, mode source
 	return pkg, nil
 }
 
+var goVersionRx = regexp.MustCompile(`^go([1-9][0-9]*)\.(0|[1-9][0-9]*)$`)
+
 func doTypeCheck(ctx context.Context, snapshot *snapshot, m *Metadata, mode source.ParseMode, deps map[PackagePath]*packageHandle, astFilter *unexportedFilter) (*pkg, error) {
 	ctx, done := event.Start(ctx, "cache.typeCheck", tag.Package.Of(string(m.ID)))
 	defer done()
@@ -515,6 +518,15 @@ func doTypeCheck(ctx context.Context, snapshot *snapshot, m *Metadata, mode sour
 			return depPkg.types, nil
 		}),
 	}
+	if pkg.m.Module != nil && pkg.m.Module.GoVersion != "" {
+		goVersion := "go" + pkg.m.Module.GoVersion
+		// types.NewChecker panics if GoVersion is invalid. An unparsable mod
+		// file should probably stop us before we get here, but double check
+		// just in case.
+		if goVersionRx.MatchString(goVersion) {
+			typesinternal.SetGoVersion(cfg, goVersion)
+		}
+	}
 
 	if mode != source.ParseFull {
 		cfg.DisableUnusedImportCheck = true

internal/typesinternal/types.go

@@ -48,3 +48,5 @@ func ReadGo116ErrorData(err types.Error) (code ErrorCode, start, end token.Pos,
 	}
 	return ErrorCode(data[0]), token.Pos(data[1]), token.Pos(data[2]), true
 }
+
+var SetGoVersion = func(conf *types.Config, version string) bool { return false }

internal/typesinternal/types_118.go

@@ -0,0 +1,19 @@
+// Copyright 2021 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.
+
+//go:build go1.18
+// +build go1.18
+
+package typesinternal
+
+import (
+	"go/types"
+)
+
+func init() {
+	SetGoVersion = func(conf *types.Config, version string) bool {
+		conf.GoVersion = version
+		return true
+	}
+}