Add default-style parameter to math.equation

crates/typst-layout/src/math/text.rs

@@ -4,7 +4,7 @@ use ecow::EcoString;
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain, SymbolElem};
 use typst_library::layout::{Abs, Size};
-use typst_library::math::{EquationElem, MathSize, MathVariant};
+use typst_library::math::{EquationElem, MathSize, MathStyle, MathVariant};
 use typst_library::text::{
     BottomEdge, BottomEdgeMetric, TextElem, TopEdge, TopEdgeMetric,
 };
@@ -187,14 +187,21 @@ fn styled_char(styles: StyleChain, c: char, auto_italic: bool) -> char {
 
     let variant = EquationElem::variant_in(styles);
     let bold = EquationElem::bold_in(styles);
+    let default_style = EquationElem::default_style_in(styles);
+    let default_italic = match c {
+        'a'..='z' | 'ħ' | 'ı' | 'ȷ' | 
+        'α'..='ω' | 'ϵ' | 'ϑ' | 'ϰ' | 'ϕ' | 'ϱ' | 'ϖ' => 
+            matches!(default_style, MathStyle::Iso | MathStyle::Tex | MathStyle::French),
+        'A'..='Z' => 
+            matches!(default_style, MathStyle::Iso | MathStyle::Tex),
+        'Α'..='Ω' => 
+            matches!(default_style, MathStyle::Iso),
+        '∂' => 
+            matches!(default_style, MathStyle::Tex | MathStyle::French),
+        _ => false
+    };
     let italic = EquationElem::italic_in(styles).unwrap_or(
-        auto_italic
+        auto_italic && default_italic && matches!(variant, Sans | Serif),
-            && matches!(
-                c,
-                'a'..='z' | 'ħ' | 'ı' | 'ȷ' | 'A'..='Z' |
-                'α'..='ω' | '∂' | 'ϵ' | 'ϑ' | 'ϰ' | 'ϕ' | 'ϱ' | 'ϖ'
-            )
-            && matches!(variant, Sans | Serif),
     );
 
     if let Some(c) = basic_exception(c) {

crates/typst-library/src/math/equation.rs

@@ -14,7 +14,7 @@ use crate::layout::{
     AlignElem, Alignment, BlockElem, InlineElem, OuterHAlignment, SpecificAlignment,
     VAlignment,
 };
-use crate::math::{MathSize, MathVariant};
+use crate::math::{MathSize, MathStyle, MathVariant};
 use crate::model::{Numbering, Outlinable, ParLine, Refable, Supplement};
 use crate::text::{FontFamily, FontList, FontWeight, LocalName, TextElem};
 
@@ -52,6 +52,10 @@ pub struct EquationElem {
     #[default(false)]
     pub block: bool,
 
+    /// The rule determining which letters and symbols are italic by default.
+    #[default(MathStyle::Tex)]
+    pub default_style: MathStyle,
+
     /// How to [number]($numbering) block-level equations.
     ///
     /// ```example

crates/typst-library/src/math/style.rs

@@ -252,3 +252,19 @@ pub enum MathVariant {
     Mono,
     Bb,
 }
+
+
+/// A rule describing which letters and symbols are italic by default.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Cast, Hash)]
+// #[derive(Serialize, Deserialize, Cast)]
+// #[serde(rename_all = "kebab-case")]
+pub enum MathStyle {
+    // Every latin or greek letter italic, [partial] upright.
+    Iso,
+    // Everything but capital greek letters italic.
+    Tex,
+    // Lowercase letters and [partial] italic.
+    French,
+    // Everything upright.
+    Upright
+}

tests/suite/math/style.typ

@@ -1,7 +1,16 @@
 // Test text styling in math.
 
 --- math-style-italic-default ---
-// Test italic defaults.
+// Test italic defaults for all `default-style`s.
+$a, A, delta, ϵ, partial, Delta, ϴ$
+
+#set math.equation(default-style: "iso")
+$a, A, delta, ϵ, partial, Delta, ϴ$
+
+#set math.equation(default-style: "french")
+$a, A, delta, ϵ, partial, Delta, ϴ$
+
+#set math.equation(default-style: "upright")
 $a, A, delta, ϵ, partial, Delta, ϴ$
 
 --- math-style ---