internal/lsp: support Check For Upgrades in vendor mode

Essentially the same bug, and fix, as golang/go#38711.

Fixes golang/go#44756.

Change-Id: Ib4aaa73c2036e23f7afd7e48b685096039759ef9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/311909
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

gopls/internal/regtest/codelens/codelens_test.go

@@ -5,6 +5,7 @@
 package codelens
 
 import (
+	"fmt"
 	"runtime"
 	"strings"
 	"testing"
@@ -103,7 +104,7 @@ var Goodbye error
 -- go.mod --
 module mod.com
 
-go 1.12
+go 1.14
 
 require golang.org/x/hello v1.2.3
 -- go.sum --
@@ -121,7 +122,7 @@ func main() {
 
 	const wantGoMod = `module mod.com
 
-go 1.12
+go 1.14
 
 require golang.org/x/hello v1.3.3
 `
@@ -159,20 +160,25 @@ require golang.org/x/hello v1.3.3
 			})
 		})
 	}
-	t.Run("Upgrade individual dependency", func(t *testing.T) {
-		WithOptions(ProxyFiles(proxyWithLatest)).Run(t, shouldUpdateDep, func(t *testing.T, env *Env) {
-			env.OpenFile("go.mod")
-			env.ExecuteCodeLensCommand("go.mod", command.CheckUpgrades)
-			d := &protocol.PublishDiagnosticsParams{}
-			env.Await(OnceMet(env.DiagnosticAtRegexpWithMessage("go.mod", `require`, "can be upgraded"),
-				ReadDiagnostics("go.mod", d)))
-			env.ApplyQuickFixes("go.mod", d.Diagnostics)
-			env.Await(env.DoneWithChangeWatchedFiles())
-			if got := env.Editor.BufferText("go.mod"); got != wantGoMod {
-				t.Fatalf("go.mod upgrade failed:\n%s", tests.Diff(t, wantGoMod, got))
-			}
+	for _, vendoring := range []bool{false, true} {
+		t.Run(fmt.Sprintf("Upgrade individual dependency vendoring=%v", vendoring), func(t *testing.T) {
+			WithOptions(ProxyFiles(proxyWithLatest)).Run(t, shouldUpdateDep, func(t *testing.T, env *Env) {
+				if vendoring {
+					env.RunGoCommand("mod", "vendor")
+				}
+				env.OpenFile("go.mod")
+				env.ExecuteCodeLensCommand("go.mod", command.CheckUpgrades)
+				d := &protocol.PublishDiagnosticsParams{}
+				env.Await(OnceMet(env.DiagnosticAtRegexpWithMessage("go.mod", `require`, "can be upgraded"),
+					ReadDiagnostics("go.mod", d)))
+				env.ApplyQuickFixes("go.mod", d.Diagnostics)
+				env.Await(env.DoneWithChangeWatchedFiles())
+				if got := env.Editor.BufferText("go.mod"); got != wantGoMod {
+					t.Fatalf("go.mod upgrade failed:\n%s", tests.Diff(t, wantGoMod, got))
+				}
+			})
 		})
-	})
+	}
 }
 
 func TestUnusedDependenciesCodelens(t *testing.T) {

internal/lsp/cache/snapshot.go

@@ -351,22 +351,25 @@ func (s *snapshot) goCommandInvocation(ctx context.Context, flags source.Invocat
 		return "", nil, cleanup, err
 	}
 
-	mutableModFlag := ""
-	if s.view.goversion >= 16 {
-		mutableModFlag = "mod"
-	}
+	// If the mod flag isn't set, populate it based on the mode and workspace.
+	if inv.ModFlag == "" {
+		mutableModFlag := ""
+		if s.view.goversion >= 16 {
+			mutableModFlag = "mod"
+		}
 
-	switch mode {
-	case source.LoadWorkspace, source.Normal:
-		if vendorEnabled {
-			inv.ModFlag = "vendor"
-		} else if !allowModfileModificationOption {
-			inv.ModFlag = "readonly"
-		} else {
+		switch mode {
+		case source.LoadWorkspace, source.Normal:
+			if vendorEnabled {
+				inv.ModFlag = "vendor"
+			} else if !allowModfileModificationOption {
+				inv.ModFlag = "readonly"
+			} else {
+				inv.ModFlag = mutableModFlag
+			}
+		case source.UpdateUserModFile, source.WriteTemporaryModFile:
 			inv.ModFlag = mutableModFlag
 		}
-	case source.UpdateUserModFile, source.WriteTemporaryModFile:
-		inv.ModFlag = mutableModFlag
 	}
 
 	wantTempMod := mode != source.UpdateUserModFile

internal/lsp/command.go

@@ -584,6 +584,7 @@ func (s *Server) getUpgrades(ctx context.Context, snapshot source.Snapshot, uri
 		Verb:       "list",
 		Args:       append([]string{"-m", "-u", "-json"}, modules...),
 		WorkingDir: filepath.Dir(uri.Filename()),
+		ModFlag:    "readonly",
 	})
 	if err != nil {
 		return nil, err