Fixed rule conflict management. Added User guide for formatting

tests/core/formatting/test_dsl_parser.py

@@ -11,6 +11,7 @@ from myfasthtml.core.formatting.dataclasses import (
   BooleanFormatter,
   TextFormatter,
   EnumFormatter,
+  ConstantFormatter,
 )
 from myfasthtml.core.formatting.dsl import (
   parse_dsl,
@@ -342,11 +343,23 @@ column status:
     format.enum(source={"draft": "Brouillon", "published": "Publie"})
 """
     rules = parse_dsl(dsl)
-    
+
     formatter = rules[0].rule.formatter
     assert isinstance(formatter, EnumFormatter)
     assert formatter.source == {"draft": "Brouillon", "published": "Publie"}
 
+  def test_i_can_parse_format_constant(self):
+    """Test parsing format.constant with fixed value."""
+    dsl = """
+column placeholder:
+    format.constant(value="N/A")
+"""
+    rules = parse_dsl(dsl)
+
+    formatter = rules[0].rule.formatter
+    assert isinstance(formatter, ConstantFormatter)
+    assert formatter.value == "N/A"
+
 
 # =============================================================================
 # Condition Tests
@@ -379,9 +392,9 @@ column amount:
     assert condition is not None
     assert condition.operator == operator
   
-  @pytest.mark.parametrize("unary_op", ["isempty", "isnotempty"])
+  @pytest.mark.parametrize("unary_op", ["isempty", "isnotempty", "isnan"])
   def test_i_can_parse_unary_conditions(self, unary_op):
-    """Test parsing unary conditions (isempty, isnotempty)."""
+    """Test parsing unary conditions (isempty, isnotempty, isnan)."""
     dsl = f"""
 column name:
     style("neutral") if value {unary_op}

tests/core/formatting/test_engine.py

@@ -215,6 +215,75 @@ class TestConflictResolution:
 
         assert "color: red" in css
 
+    def test_style_and_formatter_fusion(self):
+        """
+        Test that style and formatter can come from different rules.
+
+        Scenario:
+        - Rule 1: format("EUR") - unconditional formatter
+        - Rule 2: style("secondary") if value > col.X - conditional style
+
+        When condition is met:
+        - Style from Rule 2 (higher specificity for style)
+        - Formatter from Rule 1 (only rule with formatter)
+        - Both should be applied (fusion)
+        """
+        engine = FormattingEngine()
+        rules = [
+            FormatRule(formatter=NumberFormatter(precision=2, suffix=" €")),  # unconditional
+            FormatRule(
+                condition=Condition(operator=">", value={"col": "budget"}),
+                style=Style(preset="secondary")  # conditional
+            ),
+        ]
+        row_data = {"budget": 100}
+
+        # Case 1: Condition met (value > budget)
+        css, formatted = engine.apply_format(rules, cell_value=150, row_data=row_data)
+
+        assert css is not None
+        assert "var(--color-secondary)" in css  # Style from Rule 2
+        assert formatted == "150.00 €"  # Formatter from Rule 1
+
+        # Case 2: Condition not met (value <= budget)
+        css, formatted = engine.apply_format(rules, cell_value=50, row_data=row_data)
+
+        assert css is None  # No style (Rule 2 doesn't match)
+        assert formatted == "50.00 €"  # Formatter from Rule 1 still applies
+
+    def test_multiple_styles_and_formatters_highest_specificity_wins(self):
+        """
+        Test that style and formatter are resolved independently with specificity.
+
+        Rules:
+        - Rule 1: style("neutral") - unconditional
+        - Rule 2: format("EUR") - unconditional
+        - Rule 3: style("error") if value < 0 - conditional style
+        - Rule 4: format.number(precision=0) if value < 0 - conditional formatter
+
+        When value < 0:
+        - Style from Rule 3 (higher specificity)
+        - Formatter from Rule 4 (higher specificity)
+        """
+        engine = FormattingEngine()
+        rules = [
+            FormatRule(style=Style(preset="neutral")),
+            FormatRule(formatter=NumberFormatter(precision=2, suffix=" €")),
+            FormatRule(
+                condition=Condition(operator="<", value=0),
+                style=Style(preset="error")
+            ),
+            FormatRule(
+                condition=Condition(operator="<", value=0),
+                formatter=NumberFormatter(precision=0, suffix=" €")
+            ),
+        ]
+
+        css, formatted = engine.apply_format(rules, cell_value=-5.67)
+
+        assert "var(--color-error)" in css  # Rule 3 wins for style
+        assert formatted == "-6 €"  # Rule 4 wins for formatter (precision=0)
+
 
 class TestWithRowData:
     def test_condition_with_column_reference(self):