gopls/internal/lsp: tolerate missing end position in RelatedInformation

Fix the panic reported in #56270, allowing RelatedInformation.End to be
missing.

Fixes golang/go#56270

Change-Id: I5f2dc27cf149c324f39ddbb056862434fe38f730
Reviewed-on: https://go-review.googlesource.com/c/tools/+/443337
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>

go/analysis/diagnostic.go

@@ -37,7 +37,7 @@ type Diagnostic struct {
 // declaration.
 type RelatedInformation struct {
 	Pos     token.Pos
-	End     token.Pos
+	End     token.Pos // optional
 	Message string
 }
 

gopls/internal/lsp/cache/errors.go

@@ -334,7 +334,11 @@ func relatedInformation(pkg *pkg, fset *token.FileSet, diag *analysis.Diagnostic
 		if tokFile == nil {
 			return nil, bug.Errorf("no file for %q diagnostic position", diag.Category)
 		}
-		spn, err := span.NewRange(tokFile, related.Pos, related.End).Span()
+		end := related.End
+		if !end.IsValid() {
+			end = related.Pos
+		}
+		spn, err := span.NewRange(tokFile, related.Pos, end).Span()
 		if err != nil {
 			return nil, err
 		}

gopls/internal/lsp/regtest/env.go

@@ -11,9 +11,9 @@ import (
 	"sync"
 	"testing"
 
-	"golang.org/x/tools/internal/jsonrpc2/servertest"
 	"golang.org/x/tools/gopls/internal/lsp/fake"
 	"golang.org/x/tools/gopls/internal/lsp/protocol"
+	"golang.org/x/tools/internal/jsonrpc2/servertest"
 )
 
 // Env holds the building blocks of an editor testing environment, providing
@@ -119,7 +119,7 @@ func (s State) String() string {
 	for name, params := range s.diagnostics {
 		fmt.Fprintf(&b, "\t%s (version %d):\n", name, int(params.Version))
 		for _, d := range params.Diagnostics {
-			fmt.Fprintf(&b, "\t\t(%d, %d): %s\n", int(d.Range.Start.Line), int(d.Range.Start.Character), d.Message)
+			fmt.Fprintf(&b, "\t\t(%d, %d) [%s]: %s\n", int(d.Range.Start.Line), int(d.Range.Start.Character), d.Source, d.Message)
 		}
 	}
 	b.WriteString("\n")

gopls/internal/lsp/source/options.go

@@ -1306,8 +1306,8 @@ func (r *OptionResult) asBoolMap() map[string]bool {
 	}
 	m := make(map[string]bool)
 	for a, enabled := range all {
-		if enabled, ok := enabled.(bool); ok {
-			m[a] = enabled
+		if e, ok := enabled.(bool); ok {
+			m[a] = e
 		} else {
 			r.parseErrorf("invalid type %T for map key %q", enabled, a)
 			return m

gopls/internal/regtest/misc/staticcheck_test.go

@@ -74,3 +74,40 @@ var FooErr error = errors.New("foo")
 		)
 	})
 }
+
+// Test for golang/go#56270: an analysis with related info should not panic if
+// analysis.RelatedInformation.End is not set.
+func TestStaticcheckRelatedInfo(t *testing.T) {
+	testenv.NeedsGo1Point(t, 17) // staticcheck is only supported at Go 1.17+
+	const files = `
+-- go.mod --
+module mod.test
+
+go 1.18
+-- p.go --
+package p
+
+import (
+	"fmt"
+)
+
+func Foo(enabled interface{}) {
+	if enabled, ok := enabled.(bool); ok {
+	} else {
+		_ = fmt.Sprintf("invalid type %T", enabled) // enabled is always bool here
+	}
+}
+`
+
+	WithOptions(
+		Settings{"staticcheck": true},
+	).Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("p.go")
+		env.Await(
+			OnceMet(
+				env.DoneWithOpen(),
+				env.DiagnosticAtRegexpFromSource("p.go", ", (enabled)", "SA9008"),
+			),
+		)
+	})
+}

gopls/internal/span/token.go

@@ -19,7 +19,9 @@ type Range struct {
 	Start, End token.Pos   // both IsValid()
 }
 
-// NewRange creates a new Range from a token.File and two valid positions within it.
+// NewRange creates a new Range from a token.File and two positions within it.
+// The given start position must be valid; if end is invalid, start is used as
+// the end position.
 //
 // (If you only have a token.FileSet, use file = fset.File(start). But
 // most callers know exactly which token.File they're dealing with and
@@ -33,7 +35,7 @@ func NewRange(file *token.File, start, end token.Pos) Range {
 		panic("invalid start token.Pos")
 	}
 	if !end.IsValid() {
-		panic("invalid end token.Pos")
+		end = start
 	}
 
 	// TODO(adonovan): ideally we would make this stronger assertion: