[gopls-release-branch.0.3] internal/lsp/cache: handle invalid analysis Pos

The nilness analysis gives us diagnostics with invalid start Pos. We can
just ignore those and log them.

Add a missing error check while I'm in here.

Change-Id: I4a205f253a9e47ec1513ff6299479f52e414a48c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/216724
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
(cherry picked from commit e1fd582)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/216845

Author: heschi

internal/lsp/cache/analysis.go

@@ -19,6 +19,7 @@ import (
 	"golang.org/x/tools/internal/lsp/telemetry"
 	"golang.org/x/tools/internal/memoize"
 	"golang.org/x/tools/internal/telemetry/log"
+	"golang.org/x/tools/internal/telemetry/tag"
 	errors "golang.org/x/xerrors"
 )
 
@@ -319,13 +320,15 @@ func runAnalysis(ctx context.Context, fset *token.FileSet, analyzer *analysis.An
 		return data
 	}
 	data.result, data.err = pass.Analyzer.Run(pass)
-	if data.err == nil {
-		if got, want := reflect.TypeOf(data.result), pass.Analyzer.ResultType; got != want {
-			data.err = errors.Errorf(
-				"internal error: on package %s, analyzer %s returned a result of type %v, but declared ResultType %v",
-				pass.Pkg.Path(), pass.Analyzer, got, want)
-			return data
-		}
+	if data.err != nil {
+		return data
+	}
+
+	if got, want := reflect.TypeOf(data.result), pass.Analyzer.ResultType; got != want {
+		data.err = errors.Errorf(
+			"internal error: on package %s, analyzer %s returned a result of type %v, but declared ResultType %v",
+			pass.Pkg.Path(), pass.Analyzer, got, want)
+		return data
 	}
 
 	// disallow calls after Run
@@ -339,8 +342,8 @@ func runAnalysis(ctx context.Context, fset *token.FileSet, analyzer *analysis.An
 	for _, diag := range diagnostics {
 		srcErr, err := sourceError(ctx, fset, pkg, diag)
 		if err != nil {
-			data.err = err
-			return data
+			log.Error(ctx, "unable to compute analysis error position", err, tag.Of("category", diag.Category), telemetry.Package.Of(pkg.ID()))
+			continue
 		}
 		data.diagnostics = append(data.diagnostics, srcErr)
 	}

internal/span/token.go

@@ -61,6 +61,9 @@ func (r Range) IsPoint() bool {
 // It will fill in all the members of the Span, calculating the line and column
 // information.
 func (r Range) Span() (Span, error) {
+	if !r.Start.IsValid() {
+		return Span{}, fmt.Errorf("start pos is not valid")
+	}
 	f := r.FileSet.File(r.Start)
 	if f == nil {
 		return Span{}, fmt.Errorf("file not found in FileSet")