Fixes for code block background painting, and add line numbers to Code Editor dialog

bouquin/code_block_editor_dialog.py

@@ -1,5 +1,8 @@
 from __future__ import annotations
 
+from PySide6.QtCore import QSize, QRect, Qt
+from PySide6.QtGui import QPainter, QPalette, QColor, QFont, QFontMetrics
+
 from PySide6.QtWidgets import (
     QDialog,
     QVBoxLayout,
@@ -7,11 +10,126 @@ from PySide6.QtWidgets import (
     QDialogButtonBox,
     QComboBox,
     QLabel,
+    QWidget,
 )
 
 from . import strings
 
 
+class _LineNumberArea(QWidget):
+    def __init__(self, editor: "CodeEditorWithLineNumbers"):
+        super().__init__(editor)
+        self._editor = editor
+
+    def sizeHint(self) -> QSize:  # type: ignore[override]
+        return QSize(self._editor.line_number_area_width(), 0)
+
+    def paintEvent(self, event):  # type: ignore[override]
+        self._editor.line_number_area_paint_event(event)
+
+
+class CodeEditorWithLineNumbers(QPlainTextEdit):
+    """QPlainTextEdit with a non-selectable line-number gutter on the left."""
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self._line_number_area = _LineNumberArea(self)
+
+        self.blockCountChanged.connect(self._update_line_number_area_width)
+        self.updateRequest.connect(self._update_line_number_area)
+        self.cursorPositionChanged.connect(self._line_number_area.update)
+
+        self._update_line_number_area_width()
+
+    # ---- layout / sizing -------------------------------------------------
+
+    def line_number_area_width(self) -> int:
+        # Enough digits for large-ish code blocks.
+        digits = max(2, len(str(max(1, self.blockCount()))))
+        fm = QFontMetrics(self._line_number_font())
+        return fm.horizontalAdvance("9" * digits) + 8
+
+    def _line_number_font(self) -> QFont:
+        """Font to use for line numbers (slightly smaller than main text)."""
+        font = self.font()
+        if font.pointSize() > 0:
+            font.setPointSize(font.pointSize() - 1)
+        else:
+            # fallback for pixel-sized fonts
+            font.setPointSizeF(font.pointSizeF() * 0.9)
+        return font
+
+    def _update_line_number_area_width(self) -> None:
+        margin = self.line_number_area_width()
+        self.setViewportMargins(margin, 0, 0, 0)
+
+    def resizeEvent(self, event):  # type: ignore[override]
+        super().resizeEvent(event)
+        cr = self.contentsRect()
+        self._line_number_area.setGeometry(
+            QRect(cr.left(), cr.top(), self.line_number_area_width(), cr.height())
+        )
+
+    def _update_line_number_area(self, rect, dy) -> None:
+        if dy:
+            self._line_number_area.scroll(0, dy)
+        else:
+            self._line_number_area.update(
+                0, rect.y(), self._line_number_area.width(), rect.height()
+            )
+
+        if rect.contains(self.viewport().rect()):
+            self._update_line_number_area_width()
+
+    # ---- painting --------------------------------------------------------
+
+    def line_number_area_paint_event(self, event) -> None:
+        painter = QPainter(self._line_number_area)
+        painter.fillRect(event.rect(), self.palette().base())
+
+        # Use a slightly smaller font for numbers
+        painter.setFont(self._line_number_font())
+
+        # Faded colour: same blend used for completed-task text in
+        # MarkdownHighlighter (text colour towards background).
+        pal = self.palette()
+        text_fg = pal.color(QPalette.Text)
+        text_bg = pal.color(QPalette.Base)
+        t = 0.55  # same factor as completed_task_format
+        faded = QColor(
+            int(text_fg.red() * (1.0 - t) + text_bg.red() * t),
+            int(text_fg.green() * (1.0 - t) + text_bg.green() * t),
+            int(text_fg.blue() * (1.0 - t) + text_bg.blue() * t),
+        )
+        painter.setPen(faded)
+
+        block = self.firstVisibleBlock()
+        block_number = block.blockNumber()
+        top = self.blockBoundingGeometry(block).translated(self.contentOffset()).top()
+        bottom = top + self.blockBoundingRect(block).height()
+        fm = self.fontMetrics()
+        line_height = fm.height()
+        right_margin = self._line_number_area.width() - 4
+
+        while block.isValid() and top <= event.rect().bottom():
+            if block.isVisible() and bottom >= event.rect().top():
+                number = str(block_number + 1)
+                painter.setPen(self.palette().text().color())
+                painter.drawText(
+                    0,
+                    int(top),
+                    right_margin,
+                    line_height,
+                    Qt.AlignRight | Qt.AlignVCenter,
+                    number,
+                )
+
+            block = block.next()
+            top = bottom
+            bottom = top + self.blockBoundingRect(block).height()
+            block_number += 1
+
+
 class CodeBlockEditorDialog(QDialog):
     def __init__(
         self, code: str, language: str | None, parent=None, allow_delete: bool = False
@@ -20,7 +138,7 @@ class CodeBlockEditorDialog(QDialog):
         self.setWindowTitle(strings._("edit_code_block"))
 
         self.setMinimumSize(650, 650)
-        self._code_edit = QPlainTextEdit(self)
+        self._code_edit = CodeEditorWithLineNumbers(self)
         self._code_edit.setPlainText(code)
 
         # Track whether the user clicked "Delete"