Fix `str.trim(regex,at:end)` when the whole string is matched (#3730)

2 files changed, 31 insertions, 11 deletions

diff --git a/crates/typst/src/foundations/str.rs b/crates/typst/src/foundations/str.rs
index 897ca45b..515a4e21 100644
--- a/crates/typst/src/foundations/str.rs
+++ b/crates/typst/src/foundations/str.rs
@@ -491,11 +491,11 @@ impl Str {
     #[func]
     pub fn trim(
         &self,
-        /// The pattern to search for.
+        /// The pattern to search for. If `{none}`, trims white spaces.
         #[default]
         pattern: Option<StrPattern>,
-        /// Can be `start` or `end` to only trim the start or end of the string.
-        /// If omitted, both sides are trimmed.
+        /// Can be `{start}` or `{end}` to only trim the start or end of the
+        /// string. If omitted, both sides are trimmed.
         #[named]
         at: Option<StrSide>,
         /// Whether to repeatedly removes matches of the pattern or just once.
@@ -535,16 +535,16 @@ impl Str {
             }
             Some(StrPattern::Regex(re)) => {
                 let s = self.as_str();
-                let mut last = 0;
+                let mut last = None;
                 let mut range = 0..s.len();
 
                 for m in re.find_iter(s) {
                     // Does this match follow directly after the last one?
-                    let consecutive = last == m.start();
+                    let consecutive = last == Some(m.start());
 
-                    // As long as we're consecutive and still trimming at the
-                    // start, trim.
-                    start &= consecutive;
+                    // As long as we're at the beginning or in a consecutive run
+                    // of matches, and we're still trimming at the start, trim.
+                    start &= m.start() == 0 || consecutive;
                     if start {
                         range.start = m.end();
                         start &= repeat;
@@ -556,11 +556,11 @@ impl Str {
                         range.end = m.start();
                     }
 
-                    last = m.end();
+                    last = Some(m.end());
                 }
 
                 // Is the last match directly at the end?
-                if last < s.len() {
+                if last.is_some_and(|last| last < s.len()) {
                     range.end = s.len();
                 }
 
diff --git a/tests/typ/compiler/string.typ b/tests/typ/compiler/string.typ
index ed1296a7..949a2154 100644
--- a/tests/typ/compiler/string.typ
+++ b/tests/typ/compiler/string.typ
@@ -180,17 +180,31 @@
 #"123".replace("123", (1, 2, 3))
 
 ---
-// Test the `trim` method.
+// Test the `trim` method; the pattern is not provided.
 #let str = "Typst, LaTeX, Word, InDesign"
 #let array = ("Typst", "LaTeX", "Word", "InDesign")
 #test(str.split(",").map(s => s.trim()), array)
 #test("".trim(), "")
+#test("  ".trim(), "")
+#test("\t".trim(), "")
+#test("\n".trim(), "")
+#test("\t \n".trim(), "")
 #test(" abc ".trim(at: start), "abc ")
+#test("\tabc ".trim(at: start), "abc ")
+#test("abc\n".trim(at: end), "abc")
 #test(" abc ".trim(at: end, repeat: true), " abc")
 #test("  abc".trim(at: start, repeat: false), "abc")
+
+---
+// Test the `trim` method; the pattern is a string.
 #test("aabcaa".trim("a", repeat: false), "abca")
 #test("aabca".trim("a", at: start), "bca")
 #test("aabcaa".trim("a", at: end, repeat: false), "aabca")
+#test(" abc\n".trim("\n"), " abc")
+#test("whole".trim("whole", at: start), "")
+
+---
+// Test the `trim` method; the pattern is a regex.
 #test("".trim(regex(".")), "")
 #test("123abc456".trim(regex("\d")), "abc")
 #test("123abc456".trim(regex("\d"), repeat: false), "23abc45")
@@ -201,6 +215,12 @@
 #test("123abc456".trim(regex("\d+"), at: end, repeat: false), "123abc")
 #test("123abc456".trim(regex("\d{1,2}$"), repeat: false), "123abc4")
 #test("hello world".trim(regex(".")), "")
+#test("12306".trim(regex("\d"), at: start), "")
+#test("12306abc".trim(regex("\d"), at: start), "abc")
+#test("whole".trim(regex("whole"), at: start), "")
+#test("12306".trim(regex("\d"), at: end), "")
+#test("abc12306".trim(regex("\d"), at: end), "abc")
+#test("whole".trim(regex("whole"), at: end), "")
 
 ---
 // Error: 17-21 expected either `start` or `end`