gopls/internal/lsp/work: don't crash when hovering over broken mod dir

Guard against modfiles without a module directive.

Fixes golang/go#60821

Change-Id: I91661b2abea916db55a81323fc26dcd4f2f0516c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/503436
gopls-CI: kokoro <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: findleyr

gopls/internal/lsp/cache/mod.go

@@ -400,7 +400,7 @@ func (s *snapshot) matchErrorToModule(ctx context.Context, pm *source.ParsedModu
 		// Show the error on the module declaration, if one exists, or
 		// just the first line of the file.
 		var start, end int
-		if pm.File.Module != nil {
+		if pm.File.Module != nil && pm.File.Module.Syntax != nil {
 			syntax := pm.File.Module.Syntax
 			start, end = syntax.Start.Byte, syntax.End.Byte
 		}

gopls/internal/lsp/mod/diagnostics.go

@@ -331,7 +331,13 @@ func ModVulnerabilityDiagnostics(ctx context.Context, snapshot source.Snapshot,
 	// TODO(hyangah): place this diagnostic on the `go` directive or `toolchain` directive
 	// after https://go.dev/issue/57001.
 	const diagnoseStdLib = false
-	if diagnoseStdLib {
+
+	// If diagnosing the stdlib, add standard library vulnerability diagnostics
+	// on the module declaration.
+	//
+	// Only proceed if we have a valid module declaration on which to position
+	// the diagnostics.
+	if diagnoseStdLib && pm.File.Module != nil && pm.File.Module.Syntax != nil {
 		// Add standard library vulnerabilities.
 		stdlibVulns := vulnsByModule["stdlib"]
 		if len(stdlibVulns) == 0 {

gopls/internal/lsp/work/hover.go

@@ -52,6 +52,9 @@ func Hover(ctx context.Context, snapshot source.Snapshot, fh source.FileHandle,
 	if err != nil {
 		return nil, fmt.Errorf("getting modfile handle: %w", err)
 	}
+	if pm.File.Module == nil {
+		return nil, fmt.Errorf("modfile has no module declaration")
+	}
 	mod := pm.File.Module.Mod
 
 	// Get the range to highlight for the hover.

gopls/internal/regtest/misc/hover_test.go

@@ -415,3 +415,23 @@ func TestHoverLinknameDirective(t *testing.T) {
 		}
 	})
 }
+
+func TestHoverGoWork_Issue60821(t *testing.T) {
+	const files = `
+-- go.work --
+go 1.19
+
+use (
+	moda
+	modb
+)
+-- moda/go.mod --
+
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("go.work")
+		// Neither of the requests below should crash gopls.
+		_, _, _ = env.Editor.Hover(env.Ctx, env.RegexpSearch("go.work", "moda"))
+		_, _, _ = env.Editor.Hover(env.Ctx, env.RegexpSearch("go.work", "modb"))
+	})
+}