internal/lsp: don't reload invalid build configurations unconditionally

Previously, we would always reload views with invalid build
configurations on every call to reloadWorkspace, even if the metadata
had no reason to be treated as invalid.

Fixes golang/go#42813

Change-Id: I9e0e493228916262908b81bc1b1ab1eb4e4eca9e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/274443
Trust: Rebecca Stambler <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: stamblerre

gopls/internal/regtest/diagnostics_test.go

@@ -1627,3 +1627,22 @@ package b
 		)
 	})
 }
+
+func TestAdHocPackagesReloading(t *testing.T) {
+	const nomod = `
+-- main.go --
+package main
+
+func main() {}
+`
+	run(t, nomod, func(t *testing.T, env *Env) {
+		env.OpenFile("main.go")
+		env.RegexpReplace("main.go", "{}", "{ var x int; }") // simulate typing
+		env.Await(
+			OnceMet(
+				CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidChange), 1),
+				NoLogMatching(protocol.Info, "packages=1"),
+			),
+		)
+	})
+}

internal/lsp/cache/snapshot.go

@@ -966,29 +966,34 @@ func (s *snapshot) AwaitInitialized(ctx context.Context) {
 
 // reloadWorkspace reloads the metadata for all invalidated workspace packages.
 func (s *snapshot) reloadWorkspace(ctx context.Context) error {
-	// If the view's build configuration is invalid, we cannot reload by
-	// package path. Just reload the directory instead.
-	if !s.ValidBuildConfiguration() {
-		return s.load(ctx, viewLoadScope("LOAD_INVALID_VIEW"))
-	}
-
 	// See which of the workspace packages are missing metadata.
 	s.mu.Lock()
+	missingMetadata := len(s.workspacePackages) == 0 || len(s.metadata) == 0
 	pkgPathSet := map[packagePath]struct{}{}
 	for id, pkgPath := range s.workspacePackages {
+		if s.metadata[id] != nil {
+			continue
+		}
+		missingMetadata = true
+
 		// Don't try to reload "command-line-arguments" directly.
 		if pkgPath == "command-line-arguments" {
 			continue
 		}
-		if s.metadata[id] == nil {
-			pkgPathSet[pkgPath] = struct{}{}
-		}
+		pkgPathSet[pkgPath] = struct{}{}
 	}
 	s.mu.Unlock()
 
+	// If the view's build configuration is invalid, we cannot reload by
+	// package path. Just reload the directory instead.
+	if missingMetadata && !s.ValidBuildConfiguration() {
+		return s.load(ctx, viewLoadScope("LOAD_INVALID_VIEW"))
+	}
+
 	if len(pkgPathSet) == 0 {
 		return nil
 	}
+
 	var pkgPaths []interface{}
 	for pkgPath := range pkgPathSet {
 		pkgPaths = append(pkgPaths, pkgPath)