internal/lsp: fix concurrent map read/write for missingmodules

This change fixes an issue with concurrent map reads and writes that occurred when determining if an import is missing the corresponding dependency in the go.mod file.

Change-Id: Ic5cf3a620b4fd84eb4a377d0e4c22edbc8f37540
Reviewed-on: https://go-review.googlesource.com/c/tools/+/221897
Run-TryBot: Rohan Challa <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>
(cherry picked from commit 115860e)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/222980
Reviewed-by: Heschi Kreinick <[email protected]>

Author: ridersofrohan

internal/lsp/source/diagnostics.go

@@ -61,10 +61,10 @@ func Diagnostics(ctx context.Context, snapshot Snapshot, ph PackageHandle, missi
 		warn = true
 	}
 
-	isMissingModule := false
+	missing := make(map[string]*modfile.Require)
 	for _, imp := range pkg.Imports() {
-		if _, ok := missingModules[imp.PkgPath()]; ok {
-			isMissingModule = true
+		if req, ok := missingModules[imp.PkgPath()]; ok {
+			missing[imp.PkgPath()] = req
 			continue
 		}
 		for dep, req := range missingModules {
@@ -77,8 +77,7 @@ func Diagnostics(ctx context.Context, snapshot Snapshot, ph PackageHandle, missi
 			// )
 			// They both are related to the same module: "golang.org/x/tools"
 			if req != nil && strings.HasPrefix(imp.PkgPath(), dep) {
-				missingModules[imp.PkgPath()] = req
-				isMissingModule = true
+				missing[imp.PkgPath()] = req
 				break
 			}
 		}
@@ -90,8 +89,8 @@ func Diagnostics(ctx context.Context, snapshot Snapshot, ph PackageHandle, missi
 		if err := clearReports(snapshot, reports, fh.File().Identity().URI); err != nil {
 			return nil, warn, err
 		}
-		if isMissingModule {
-			if err := missingModulesDiagnostics(ctx, snapshot, reports, missingModules, fh.File().Identity().URI); err != nil {
+		if len(missing) > 0 {
+			if err := missingModulesDiagnostics(ctx, snapshot, reports, missing, fh.File().Identity().URI); err != nil {
 				return nil, warn, err
 			}
 		}