Obey alignment in matrices (#892)

library/src/math/matrix.rs

@@ -272,8 +272,10 @@ fn layout_mat_body(ctx: &mut MathContext, rows: &[Vec<Content>]) -> SourceResult
         let mut y = Abs::zero();
         for ((cell, &ascent), &descent) in col.into_iter().zip(&ascents).zip(&descents) {
             let cell = cell.into_aligned_frame(ctx, &points, Align::Center);
-            let pos =
-                Point::new(x + (rcol - cell.width()) / 2.0, y + ascent - cell.ascent());
+            let pos = Point::new(
+                if points.is_empty() { x + (rcol - cell.width()) / 2.0 } else { x },
+                y + ascent - cell.ascent(),
+            );
             frame.push_frame(pos, cell);
             y += ascent + descent + row_gap;
         }

tests/typ/math/alignment.typ

@@ -2,9 +2,8 @@
 
 ---
 // Test alignment step functions.
-#set page(width: 300pt)
 $
-"abc" &= c \
+"a" &= c \
 &= c + 1 & "By definition" \
 &= d + 100 + 1000 \
 &= x && "Even longer" \
@@ -12,17 +11,83 @@ $
 
 ---
 // Test post-fix alignment.
-#set page(width: 300pt)
 $
 & "right" \
 "a very long line" \
+"left" \
+$
+
+---
+// Test no alignment.
+$
+"right" \
+"a very long line" \
+"left" \
 $
 
 ---
 // Test alternating alignment.
-#set page(width: 300pt)
 $
-"abc" & "abc abc abc" & "abc abc" \
-"abc abc" & "abc abc" & "abc" \
-"abc abc abc" & "abc" & "abc abc abc" \
+"a" & "a a a" & "a a" \
+"a a" & "a a" & "a" \
+"a a a" & "a" & "a a a" \
 $
+
+---
+// Test alternating alignment in a vector.
+$ vec(
+  "a" & "a a a" & "a a",
+  "a a" & "a a" & "a",
+  "a a a" & "a" & "a a a",
+) $
+
+---
+// Test alternating explicit alignment in a matrix.
+$ mat(
+  "a" & "a a a" & "a a";
+  "a a" & "a a" & "a";
+  "a a a" & "a" & "a a a";
+) $
+
+---
+// Test alignment in a matrix.
+$ mat(
+  "a", "a a a", "a a";
+  "a a", "a a", "a";
+  "a a a", "a", "a a a";
+) $
+
+---
+// Test explicit left alignment in a matrix.
+$ mat(
+  &"a", &"a a a", &"a a";
+  &"a a", &"a a", &"a";
+  &"a a a", &"a", &"a a a";
+) $
+
+---
+// Test explicit right alignment in a matrix.
+$ mat(
+  "a"&, "a a a"&, "a a"&;
+  "a a"&, "a a"&, "a"&;
+  "a a a"&, "a"&, "a a a"&;
+) $
+
+---
+// Test #460 equations.
+$
+a &=b & quad c&=d \
+e &=f & g&=h
+$
+
+$ mat(&a+b,c;&d, e) $
+$ mat(&a+b&,c;&d&, e) $
+$ mat(&&&a+b,c;&&&d, e) $
+$ mat(.&a+b&.,c;.....&d&....., e) $
+
+---
+// Test #454 equations.
+$ mat(-1, 1, 1; 1, -1, 1; 1, 1, -1) $
+$ mat(-1&, 1&, 1&; 1&, -1&, 1&; 1&, 1&, -1&) $
+$ mat(-1&, 1&, 1&; 1, -1, 1; 1, 1, -1) $
+$ mat(&-1, &1, &1; 1, -1, 1; 1, 1, -1) $