cmd/govim: use visual positions for diagnostics

When displaying diagnostics, the position must be visible to the user
within Vim. Some diagnostics have start/end positions that are beyond
the visible content, i.e. they are after the final \n. The user, however
will not be able to see/understand such a position. So we adjust such
positions to be before the final \n.

cmd/govim/diagnostics.go

@@ -48,12 +48,12 @@ func (v *vimstate) diagnostics() []types.Diagnostic {
 			buf = types.NewBuffer(-1, fn, byts, false)
 		}
 		for _, d := range lspDiags {
-			s, err := types.PointFromPosition(buf, d.Range.Start)
+			s, err := types.VisualPointFromPosition(buf, d.Range.Start)
 			if err != nil {
 				v.Logf("redefineDiagnostics: failed to resolve start position: %v", err)
 				continue
 			}
-			e, err := types.PointFromPosition(buf, d.Range.End)
+			e, err := types.VisualPointFromPosition(buf, d.Range.End)
 			if err != nil {
 				v.Logf("redefineDiagnostics: failed to resolve end position: %v", err)
 				continue

cmd/govim/internal/types/types.go

@@ -178,6 +178,25 @@ func PointFromPosition(b *Buffer, pos protocol.Position) (Point, error) {
 	return res, nil
 }
 
+func VisualPointFromPosition(b *Buffer, pos protocol.Position) (Point, error) {
+	p, err := PointFromPosition(b, pos)
+	if err != nil {
+		return p, err
+	}
+	c := b.Contents()
+	l := len(c)
+	if p.Offset() == l && l > 0 && c[l-1] == '\n' {
+		cc := b.tokenConvertor()
+		var newLine, newCol int
+		newLine, newCol, err = cc.ToPosition(l - 1)
+		if err != nil {
+			return p, err
+		}
+		p, err = PointFromVim(b, newLine, newCol)
+	}
+	return p, err
+}
+
 // Line refers to the 1-indexed line in the buffer. This is how Vim refers to
 // line numbers.
 func (p Point) Line() int {

cmd/govim/testdata/scenario_default/quickfix_eof.txt

@@ -17,4 +17,4 @@ package main
 
 var _ *
 -- errors.golden --
-main.go|4 col 1| expected ';', found 'EOF'
+main.go|3 col 8| expected ';', found 'EOF'