gopls/internal: don't bug.Report when given an invalid position

It's possible that the client sent us a bad protocol.Range:
that shouldn't trigger a bug report. (It's also possible that
AST fixing is perturbing positions so as to cause a valid
range not to match a parameter, but we can't easily distinguish
that case.)

Fixes golang/go#64544

Change-Id: I28f29716e8c98cf57d44cddfad5b46b1311808bb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/548738
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/internal/lsp/source/change_quote.go

@@ -27,8 +27,7 @@ import (
 func ConvertStringLiteral(pgf *ParsedGoFile, fh file.Handle, rng protocol.Range) (protocol.CodeAction, bool) {
 	startPos, endPos, err := pgf.RangePos(rng)
 	if err != nil {
-		bug.Reportf("(file=%v).RangePos(%v) failed: %v", pgf.URI, rng, err)
-		return protocol.CodeAction{}, false
+		return protocol.CodeAction{}, false // e.g. invalid range
 	}
 	path, _ := astutil.PathEnclosingInterval(pgf.File, startPos, endPos)
 	lit, ok := path[0].(*ast.BasicLit)

gopls/internal/lsp/source/change_signature.go

@@ -55,9 +55,9 @@ func RemoveUnusedParameter(ctx context.Context, fh file.Handle, rng protocol.Ran
 		return nil, fmt.Errorf("can't change signatures for packages with parse or type errors: (e.g. %s)", sample)
 	}
 
-	info := FindParam(pgf, rng)
-	if info.Decl == nil {
-		return nil, fmt.Errorf("failed to find declaration")
+	info, err := FindParam(pgf, rng)
+	if err != nil {
+		return nil, err // e.g. invalid range
 	}
 	if info.Decl.Recv != nil {
 		return nil, fmt.Errorf("can't change signature of methods (yet)")
@@ -242,20 +242,18 @@ func rewriteSignature(fset *token.FileSet, declIdx int, src0 []byte, newDecl *as
 
 // ParamInfo records information about a param identified by a position.
 type ParamInfo struct {
-	Decl       *ast.FuncDecl // enclosing func decl, or nil
+	Decl       *ast.FuncDecl // enclosing func decl (non-nil)
 	FieldIndex int           // index of Field in Decl.Type.Params, or -1
-	Field      *ast.Field    // enclosing field of Decl, or nil
+	Field      *ast.Field    // enclosing field of Decl, or nil if range not among parameters
 	NameIndex  int           // index of Name in Field.Names, or nil
 	Name       *ast.Ident    // indicated name (either enclosing, or Field.Names[0] if len(Field.Names) == 1)
 }
 
 // FindParam finds the parameter information spanned by the given range.
-func FindParam(pgf *ParsedGoFile, rng protocol.Range) ParamInfo {
-	info := ParamInfo{FieldIndex: -1, NameIndex: -1}
+func FindParam(pgf *ParsedGoFile, rng protocol.Range) (*ParamInfo, error) {
 	start, end, err := pgf.RangePos(rng)
 	if err != nil {
-		bug.Reportf("(file=%v).RangePos(%v) failed: %v", pgf.URI, rng, err)
-		return info
+		return nil, err
 	}
 
 	path, _ := astutil.PathEnclosingInterval(pgf.File, start, end)
@@ -278,9 +276,13 @@ func FindParam(pgf *ParsedGoFile, rng protocol.Range) ParamInfo {
 	}
 	// Check the conditions described in the docstring.
 	if decl == nil {
-		return info
+		return nil, fmt.Errorf("range is not within a function declaration")
+	}
+	info := &ParamInfo{
+		FieldIndex: -1,
+		NameIndex:  -1,
+		Decl:       decl,
 	}
-	info.Decl = decl
 	for fi, f := range decl.Type.Params.List {
 		if f == field {
 			info.FieldIndex = fi
@@ -299,7 +301,7 @@ func FindParam(pgf *ParsedGoFile, rng protocol.Range) ParamInfo {
 			break
 		}
 	}
-	return info
+	return info, nil
 }
 
 // signatureRewrite defines a rewritten function signature.

gopls/internal/lsp/source/fix.go

@@ -165,7 +165,7 @@ func addEmbedImport(ctx context.Context, snapshot *cache.Snapshot, fh file.Handl
 	for _, e := range protoEdits {
 		start, end, err := pgf.RangePos(e.Range)
 		if err != nil {
-			return nil, fmt.Errorf("map range: %w", err)
+			return nil, err // e.g. invalid range
 		}
 		edits = append(edits, analysis.TextEdit{
 			Pos:     start,

gopls/internal/lsp/source/inline_all.go

@@ -113,7 +113,7 @@ func inlineAllCalls(ctx context.Context, logf func(string, ...any), snapshot *ca
 		}
 		start, end, err := pgf.RangePos(ref.Range)
 		if err != nil {
-			return nil, bug.Errorf("RangePos(ref): %v", err)
+			return nil, err // e.g. invalid range
 		}
 
 		// Look for the surrounding call expression.

gopls/internal/server/code_action.go

@@ -543,15 +543,16 @@ func refactorRewrite(snapshot *cache.Snapshot, pkg *cache.Package, pgf *source.P
 //   - [start, end) is contained within an unused field or parameter name
 //   - ... of a non-method function declaration.
 func canRemoveParameter(pkg *cache.Package, pgf *source.ParsedGoFile, rng protocol.Range) bool {
-	info := source.FindParam(pgf, rng)
-	if info.Decl == nil || info.Field == nil {
-		return false
+	info, err := source.FindParam(pgf, rng)
+	if err != nil {
+		return false // e.g. invalid range
+	}
+	if info.Field == nil {
+		return false // range does not span a parameter
 	}
-
 	if info.Decl.Body == nil {
 		return false // external function
 	}
-
 	if len(info.Field.Names) == 0 {
 		return true // no names => field is unused
 	}

gopls/internal/server/semantic.go

@@ -97,7 +97,7 @@ func (s *server) semanticTokens(ctx context.Context, td protocol.TextDocumentIde
 		var err error
 		start, end, err = pgf.RangePos(*rng)
 		if err != nil {
-			return nil, fmt.Errorf("range span (%w) error for %s", err, pgf.File.Name)
+			return nil, err // e.g. invalid range
 		}
 	} else {
 		tok := pgf.Tok