From 6e0f48e192ddbd934d3aadd056810c86bcc3defd Mon Sep 17 00:00:00 2001
From: Igor Khanin <igor@khanin.biz>
Date: Wed, 28 May 2025 16:05:10 +0300
Subject: [PATCH] More precise math font autocomplete suggestions (#6316)

---
 crates/typst-ide/src/complete.rs           | 45 ++++++++++++++++++++--
 crates/typst-ide/src/tooltip.rs            |  2 +-
 crates/typst-ide/src/utils.rs              | 11 ++----
 crates/typst-library/src/text/font/book.rs |  3 ++
 4 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/crates/typst-ide/src/complete.rs b/crates/typst-ide/src/complete.rs
index 91fa53f9a..15b4296eb 100644
--- a/crates/typst-ide/src/complete.rs
+++ b/crates/typst-ide/src/complete.rs
@@ -15,7 +15,7 @@ use typst::syntax::{
     ast, is_id_continue, is_id_start, is_ident, FileId, LinkedNode, Side, Source,
     SyntaxKind,
 };
-use typst::text::RawElem;
+use typst::text::{FontFlags, RawElem};
 use typst::visualize::Color;
 use unscanny::Scanner;
 
@@ -1081,6 +1081,24 @@ fn code_completions(ctx: &mut CompletionContext, hash: bool) {
     }
 }
 
+/// See if the AST node is somewhere within a show rule applying to equations
+fn is_in_equation_show_rule(leaf: &LinkedNode<'_>) -> bool {
+    let mut node = leaf;
+    while let Some(parent) = node.parent() {
+        if_chain! {
+            if let Some(expr) = parent.get().cast::<ast::Expr>();
+            if let ast::Expr::ShowRule(show) = expr;
+            if let Some(ast::Expr::FieldAccess(field)) = show.selector();
+            if field.field().as_str() == "equation";
+            then {
+                return true;
+            }
+        }
+        node = parent;
+    }
+    false
+}
+
 /// Context for autocompletion.
 struct CompletionContext<'a> {
     world: &'a (dyn IdeWorld + 'a),
@@ -1152,10 +1170,12 @@ impl<'a> CompletionContext<'a> {
 
     /// Add completions for all font families.
     fn font_completions(&mut self) {
-        let equation = self.before_window(25).contains("equation");
+        let equation = is_in_equation_show_rule(self.leaf);
         for (family, iter) in self.world.book().families() {
-            let detail = summarize_font_family(iter);
-            if !equation || family.contains("Math") {
+            let variants: Vec<_> = iter.collect();
+            let is_math = variants.iter().any(|f| f.flags.contains(FontFlags::MATH));
+            let detail = summarize_font_family(variants);
+            if !equation || is_math {
                 self.str_completion(
                     family,
                     Some(CompletionKind::Font),
@@ -1790,4 +1810,21 @@ mod tests {
             .must_include(["r", "dashed"])
             .must_exclude(["cases"]);
     }
+
+    #[test]
+    fn test_autocomplete_fonts() {
+        test("#text(font:)", -1)
+            .must_include(["\"Libertinus Serif\"", "\"New Computer Modern Math\""]);
+
+        test("#show link: set text(font: )", -1)
+            .must_include(["\"Libertinus Serif\"", "\"New Computer Modern Math\""]);
+
+        test("#show math.equation: set text(font: )", -1)
+            .must_include(["\"New Computer Modern Math\""])
+            .must_exclude(["\"Libertinus Serif\""]);
+
+        test("#show math.equation: it => { set text(font: )\nit }", -6)
+            .must_include(["\"New Computer Modern Math\""])
+            .must_exclude(["\"Libertinus Serif\""]);
+    }
 }
diff --git a/crates/typst-ide/src/tooltip.rs b/crates/typst-ide/src/tooltip.rs
index 2638ce51b..e5e4cc19a 100644
--- a/crates/typst-ide/src/tooltip.rs
+++ b/crates/typst-ide/src/tooltip.rs
@@ -269,7 +269,7 @@ fn font_tooltip(world: &dyn IdeWorld, leaf: &LinkedNode) -> Option<Tooltip> {
             .find(|&(family, _)| family.to_lowercase().as_str() == lower.as_str());
 
         then {
-            let detail = summarize_font_family(iter);
+            let detail = summarize_font_family(iter.collect());
             return Some(Tooltip::Text(detail));
         }
     };
diff --git a/crates/typst-ide/src/utils.rs b/crates/typst-ide/src/utils.rs
index d5d584e2b..887e851f9 100644
--- a/crates/typst-ide/src/utils.rs
+++ b/crates/typst-ide/src/utils.rs
@@ -77,23 +77,20 @@ pub fn plain_docs_sentence(docs: &str) -> EcoString {
 }
 
 /// Create a short description of a font family.
-pub fn summarize_font_family<'a>(
-    variants: impl Iterator<Item = &'a FontInfo>,
-) -> EcoString {
-    let mut infos: Vec<_> = variants.collect();
-    infos.sort_by_key(|info| info.variant);
+pub fn summarize_font_family(mut variants: Vec<&FontInfo>) -> EcoString {
+    variants.sort_by_key(|info| info.variant);
 
     let mut has_italic = false;
     let mut min_weight = u16::MAX;
     let mut max_weight = 0;
-    for info in &infos {
+    for info in &variants {
         let weight = info.variant.weight.to_number();
         has_italic |= info.variant.style == FontStyle::Italic;
         min_weight = min_weight.min(weight);
         max_weight = min_weight.max(weight);
     }
 
-    let count = infos.len();
+    let count = variants.len();
     let mut detail = eco_format!("{count} variant{}.", if count == 1 { "" } else { "s" });
 
     if min_weight == max_weight {
diff --git a/crates/typst-library/src/text/font/book.rs b/crates/typst-library/src/text/font/book.rs
index 9f8acce87..cd90a08fe 100644
--- a/crates/typst-library/src/text/font/book.rs
+++ b/crates/typst-library/src/text/font/book.rs
@@ -194,6 +194,8 @@ bitflags::bitflags! {
         const MONOSPACE = 1 << 0;
         /// Glyphs have short strokes at their stems.
         const SERIF = 1 << 1;
+        /// Font face has a MATH table
+        const MATH = 1 << 2;
     }
 }
 
@@ -272,6 +274,7 @@ impl FontInfo {
 
         let mut flags = FontFlags::empty();
         flags.set(FontFlags::MONOSPACE, ttf.is_monospaced());
+        flags.set(FontFlags::MATH, ttf.tables().math.is_some());
 
         // Determine whether this is a serif or sans-serif font.
         if let Some(panose) = ttf