fix stroke thickness calculation and add tests

It didn't support negative numbers properly before.

src/utilities.typ

@@ -9,7 +9,7 @@
 // Typst 0.9.0 uses a minus sign ("−"; U+2212 MINUS SIGN) for negative numbers.
 // Before that, it used a hyphen minus ("-"; U+002D HYPHEN MINUS), so we use
 // regex alternation to match either of those.
-#let NUMBER-REGEX-STRING = "(−|-)?\\d*\\.?\\d+"
+#let NUMBER-REGEX-STRING = "(?:−|-)?\\d*\\.?\\d+"
 
 // Which positions does a cell occupy
 // (Usually just its own, but increases if colspan / rowspan
@@ -305,15 +305,11 @@
     } else if is-color(stroke) {
         1pt
     } else if type(stroke) == _stroke-type {
-        // support:
-        // - 5
-        // - 5.5
-        let maybe-float-regex = "(?:\\d+(?:\\.\\d+)?)"
         // support:
         // - 2pt / 2em / 2cm / 2in   + color
         // - 2.5pt / 2.5em / ...  + color
         // - 2pt + 3em   + color
-        let len-regex = "(?:" + maybe-float-regex + "(?:em|pt|cm|in|%)(?:\\s+\\+\\s+" + maybe-float-regex + "em)?)"
+        let len-regex = "(?:" + NUMBER-REGEX-STRING + "(?:em|pt|cm|in|%)(?:\\s+\\+\\s+" + NUMBER-REGEX-STRING + "em)?)"
         let r = regex("^" + len-regex)
         let s = repr(stroke).find(r)
 

tablex-test.typ

@@ -1,5 +1,5 @@
 #import "src/common.typ": calc-mod, _length-type
-#import "src/utilities.typ": default-if-auto, convert-length-to-pt
+#import "src/utilities.typ": default-if-auto, convert-length-to-pt, stroke-len
 #import "tablex.typ": *
 
 *Test*
@@ -860,6 +860,42 @@ Combining em and pt (with a stroke object):
 #convert-length-to-pt-test(-0.005% - 0.005pt + 0em, -0.01pt)
 #convert-length-to-pt-test(-0.005% - 0.005pt - 0.005em, -0.015pt)
 
+// Stroke thickness calculation
+#let stroke-thickness-test(
+    value, expected,
+    compare-repr: false,
+) = {
+    set text(size: 1pt)  // Set 1em to 1pt
+    style(styles => {
+        let actual = stroke-len(
+            value,
+            styles: styles,
+        )
+
+        assert(type(actual) == _length-type)
+
+        // Re-assign so we can modify the variable
+        let expected = expected
+        if compare-repr {
+            expected = repr(expected)
+            actual = repr(actual)
+        }
+        assert(expected == actual, message: "Expected " + repr(expected) + ", found " + repr(actual))
+    })
+}
+
+#stroke-thickness-test(2pt, 2pt)
+#stroke-thickness-test(2pt + 1em, 3pt)
+#stroke-thickness-test(2pt + red, 2pt)
+#stroke-thickness-test(2pt + 2em + red, 4pt)
+#stroke-thickness-test(2.2pt - 2.2em + red, 0pt)
+#stroke-thickness-test(0.005em + black, 0.005pt)
+#stroke-thickness-test(red, 1pt)
+#stroke-thickness-test((does-not-specify-thickness: 5), 1pt)
+#stroke-thickness-test((thickness: 5pt + 2em, what: 55%), 7pt)
+#stroke-thickness-test((thickness: 5pt + 2.005em, what: 55%), 7.005pt)
+#stroke-thickness-test(rect(stroke: 2.002pt - 3.003em + red).stroke, -1.001pt, compare-repr: true)
+
 *Line expansion - issue \#74:*
 
 #let wrap-for-linex-expansion-test(tabx) = {