Spreadsheet+LibSyntax: Never insert spans directly

Function `CellSyntaxHighlighter::rehighlight()` direct inserted spans
to TextDocument `m_span` vector missing out important reordering and
merging operation carried out by `TextDocument::set_spans()`.

This caused overlapping spans for a cell with only a `=` symbol
(one for the actual token and one for the highlighting) to
miscalculate `start` and `end` value and a `length` value (of
`size_t` type) with a `0-1` substraction (result: 18446744073709551615)
causing `Utf32View::substring_view()` to fail the
`!Checked<size_t>::addition_would_overflow(offset, length)` assertion

This remove the possibility to directly alter `TextDocument`'s spans
thus forcing the utilization of `HighlighterClient::do_set_spans()`
interface function.

Proper refactor have been applied to
`CellSyntaxHighlighter::rehighlight()` function

Userland/Applications/Spreadsheet/CellSyntaxHighlighter.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2022, the SerenityOS developers.
+ * Copyright (c) 2023, Matteo benetti <matteo.benetti@proton.me>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -13,17 +14,16 @@ namespace Spreadsheet {
 
 void CellSyntaxHighlighter::rehighlight(Palette const& palette)
 {
-    auto text = m_client->get_text();
+    m_client->clear_spans();
-    m_client->spans().clear();
+
-    if (!text.starts_with('=')) {
+    if (m_client->get_text().starts_with('=')) {
-        m_client->do_update();
-        return;
-    }
 
         JS::SyntaxHighlighter::rehighlight(palette);
 
+        auto spans = m_client->spans();
+
         // Highlight the '='
-    m_client->spans().empend(
+        spans.empend(
             GUI::TextRange { { 0, 0 }, { 0, 1 } },
             Gfx::TextAttributes {
                 palette.syntax_keyword(),
@@ -36,21 +36,24 @@ void CellSyntaxHighlighter::rehighlight(Palette const& palette)
         if (m_cell && m_cell->thrown_value().has_value()) {
             if (auto value = m_cell->thrown_value().value(); value.is_object() && is<JS::Error>(value.as_object())) {
                 auto& error = static_cast<JS::Error const&>(value.as_object());
-            auto& traceback = error.traceback();
+                auto& range = error.traceback().first().source_range;
-            auto& range = traceback.first().source_range;
+
-            GUI::TextRange text_range { { range.start.line - 1, range.start.column }, { range.end.line - 1, range.end.column } };
+                spans.prepend({
-            m_client->spans().prepend(
+                    GUI::TextRange { { range.start.line - 1, range.start.column }, { range.end.line - 1, range.end.column } },
-                GUI::TextDocumentSpan {
-                    text_range,
                     Gfx::TextAttributes {
                         Color::Black,
                         Color::Red,
                         false,
                     },
                     (u64)-1,
-                    false });
+                    false,
+                });
             }
         }
+
+        m_client->do_set_spans(move(spans));
+    }
+
     m_client->do_update();
 }
 }

Userland/Libraries/LibGUI/TextEditor.h

@@ -306,7 +306,6 @@ private:
     virtual void document_did_update_undo_stack() override;
 
     // ^Syntax::HighlighterClient
-    virtual Vector<TextDocumentSpan>& spans() final { return document().spans(); }
     virtual Vector<TextDocumentSpan> const& spans() const final { return document().spans(); }
     virtual void set_span_at_index(size_t index, TextDocumentSpan span) final { document().set_span_at_index(index, move(span)); }
     virtual Vector<GUI::TextDocumentFoldingRegion>& folding_regions() final { return document().folding_regions(); };

Userland/Libraries/LibSyntax/Highlighter.h

@@ -125,7 +125,6 @@ public:
     }
 
 private:
-    virtual Vector<GUI::TextDocumentSpan>& spans() override { return m_spans; }
     virtual Vector<GUI::TextDocumentSpan> const& spans() const override { return m_spans; }
     virtual void set_span_at_index(size_t index, GUI::TextDocumentSpan span) override { m_spans.at(index) = move(span); }
 

Userland/Libraries/LibSyntax/HighlighterClient.h

@@ -17,9 +17,9 @@ class HighlighterClient {
 public:
     virtual ~HighlighterClient() = default;
 
-    virtual Vector<GUI::TextDocumentSpan>& spans() = 0;
     virtual Vector<GUI::TextDocumentSpan> const& spans() const = 0;
     virtual void set_span_at_index(size_t index, GUI::TextDocumentSpan span) = 0;
+    virtual void clear_spans() { do_set_spans({}); };
 
     virtual Vector<GUI::TextDocumentFoldingRegion>& folding_regions() = 0;
     virtual Vector<GUI::TextDocumentFoldingRegion> const& folding_regions() const = 0;