internal/lsp: return an error from {Narrowest,Widest}CheckPackageHandle

This will prevent us from panicking in cases with errors.

Fixes golang/go#34824

Change-Id: I02c20655f6926ec00c1591a905ff5a107cc44192
Reviewed-on: https://go-review.googlesource.com/c/tools/+/200300
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/cache/gofile.go

@@ -110,7 +110,10 @@ func (v *view) GetActiveReverseDeps(ctx context.Context, f source.File) (results
 		if err != nil {
 			continue
 		}
-		cph := source.WidestCheckPackageHandle(cphs)
+		cph, err := source.WidestCheckPackageHandle(cphs)
+		if err != nil {
+			continue
+		}
 		for _, ph := range cph.Files() {
 			seen[ph.File().Identity().URI] = struct{}{}
 		}

internal/lsp/code_action.go

@@ -213,7 +213,10 @@ func quickFixes(ctx context.Context, view source.View, f source.File, diagnostic
 	}
 	// We get the package that source.Diagnostics would've used. This is hack.
 	// TODO(golang/go#32443): The correct solution will be to cache diagnostics per-file per-snapshot.
-	cph := source.WidestCheckPackageHandle(cphs)
+	cph, err := source.WidestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Cached(ctx)
 	if err != nil {
 		return nil, err

internal/lsp/source/completion.go

@@ -393,7 +393,10 @@ func Completion(ctx context.Context, view View, f File, pos protocol.Position, o
 	if err != nil {
 		return nil, nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, nil, err

internal/lsp/source/diagnostics.go

@@ -45,7 +45,10 @@ func Diagnostics(ctx context.Context, view View, f File, disabledAnalyses map[st
 	if err != nil {
 		return nil, "", err
 	}
-	cph := WidestCheckPackageHandle(cphs)
+	cph, err := WidestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, "", err
+	}
 
 	// If we are missing dependencies, it may because the user's workspace is
 	// not correctly configured. Report errors, if possible.
@@ -220,7 +223,10 @@ func toDiagnostic(ctx context.Context, view View, diag analysis.Diagnostic, cate
 	if err != nil {
 		return Diagnostic{}, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return Diagnostic{}, err
+	}
 	pkg, err := cph.Cached(ctx)
 	if err != nil {
 		return Diagnostic{}, err

internal/lsp/source/format.go

@@ -28,7 +28,10 @@ func Format(ctx context.Context, view View, f File) ([]protocol.TextEdit, error)
 	if err != nil {
 		return nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, err
@@ -91,7 +94,10 @@ func Imports(ctx context.Context, view View, f File) ([]protocol.TextEdit, error
 	if err != nil {
 		return nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, err
@@ -154,7 +160,10 @@ func AllImportsFixes(ctx context.Context, view View, f File) (edits []protocol.T
 	if err != nil {
 		return nil, nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, nil, err

internal/lsp/source/identifier.go

@@ -53,7 +53,10 @@ func Identifier(ctx context.Context, view View, f File, pos protocol.Position) (
 	if err != nil {
 		return nil, err
 	}
-	cph := WidestCheckPackageHandle(cphs)
+	cph, err := WidestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, err

internal/lsp/source/signature_help.go

@@ -35,7 +35,10 @@ func SignatureHelp(ctx context.Context, view View, f File, pos protocol.Position
 	if err != nil {
 		return nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, err

internal/lsp/source/symbols.go

@@ -22,7 +22,10 @@ func DocumentSymbols(ctx context.Context, view View, f File) ([]protocol.Documen
 	if err != nil {
 		return nil, err
 	}
-	cph := NarrowestCheckPackageHandle(cphs)
+	cph, err := NarrowestCheckPackageHandle(cphs)
+	if err != nil {
+		return nil, err
+	}
 	pkg, err := cph.Check(ctx)
 	if err != nil {
 		return nil, err

internal/lsp/source/util.go

@@ -56,9 +56,9 @@ func (s mappedRange) URI() span.URI {
 // By "narrowest" package, we mean the package with the fewest number of files
 // that includes the given file. This solves the problem of test variants,
 // as the test will have more files than the non-test package.
-func NarrowestCheckPackageHandle(handles []CheckPackageHandle) CheckPackageHandle {
+func NarrowestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
 	if len(handles) < 1 {
-		return nil
+		return nil, errors.Errorf("no CheckPackageHandles")
 	}
 	result := handles[0]
 	for _, handle := range handles[1:] {
@@ -66,16 +66,19 @@ func NarrowestCheckPackageHandle(handles []CheckPackageHandle) CheckPackageHandl
 			result = handle
 		}
 	}
-	return result
+	if result == nil {
+		return nil, errors.Errorf("nil CheckPackageHandles have been returned")
+	}
+	return result, nil
 }
 
 // WidestCheckPackageHandle returns the CheckPackageHandle containing the most files.
 //
 // This is useful for something like diagnostics, where we'd prefer to offer diagnostics
 // for as many files as possible.
-func WidestCheckPackageHandle(handles []CheckPackageHandle) CheckPackageHandle {
+func WidestCheckPackageHandle(handles []CheckPackageHandle) (CheckPackageHandle, error) {
 	if len(handles) < 1 {
-		return nil
+		return nil, errors.Errorf("no CheckPackageHandles")
 	}
 	result := handles[0]
 	for _, handle := range handles[1:] {
@@ -83,7 +86,10 @@ func WidestCheckPackageHandle(handles []CheckPackageHandle) CheckPackageHandle {
 			result = handle
 		}
 	}
-	return result
+	if result == nil {
+		return nil, errors.Errorf("nil CheckPackageHandles have been returned")
+	}
+	return result, nil
 }
 
 func IsGenerated(ctx context.Context, view View, uri span.URI) bool {