internal/lsp: allow narrower scope for convenience CodeActions

Code actions that apply convenience fixes were filtered by the start
line so it wasn't possible to narrow the scope to a specific range.

This change allows clients to send a specific range (or cursor position)
to filter all fixes where the range doesn't intersect with the provided
range. It also widens the diagnostic returned by fillstruct analysis.

The idea is to provide a way to narrow the scope without breaking
clients that do want to ask for code actions using the entire line.

Updates golang/go#40438

Change-Id: Ifd984a092a4a3bf0b3a2a5426d3e65023ba4eebc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/244519
Run-TryBot: Pontus Leitzler <leitzler@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

Author: leitzler

internal/lsp/analysis/fillstruct/fillstruct.go

@@ -115,8 +115,8 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		}
 		pass.Report(analysis.Diagnostic{
 			Message: fmt.Sprintf("Fill %s with default values", name),
-			Pos:     expr.Lbrace,
-			End:     expr.Rbrace,
+			Pos:     expr.Pos(),
+			End:     expr.End(),
 		})
 	})
 	return nil, nil

internal/lsp/code_action.go

@@ -364,7 +364,8 @@ func convenienceFixes(ctx context.Context, snapshot source.Snapshot, ph source.P
 		if d.URI != uri {
 			continue
 		}
-		if d.Range.Start.Line != rng.Start.Line {
+
+		if !protocol.Intersect(d.Range, rng) {
 			continue
 		}
 		action, err := diagnosticToCommandCodeAction(ctx, snapshot, d, nil, protocol.RefactorRewrite)

internal/lsp/protocol/span.go

@@ -130,6 +130,14 @@ func ComparePosition(a, b Position) int {
 	return 0
 }
 
+func Intersect(a, b Range) bool {
+	if a.Start.Line > b.End.Line || a.End.Line < b.Start.Line {
+		return false
+	}
+	return !((a.Start.Line == b.End.Line) && a.Start.Character > b.End.Character ||
+		(a.End.Line == b.Start.Line) && a.End.Character < b.Start.Character)
+}
+
 func (r Range) Format(f fmt.State, _ rune) {
 	fmt.Fprintf(f, "%v:%v-%v:%v", r.Start.Line, r.Start.Character, r.End.Line, r.End.Character)
 }