More principled indentation trimming in fixtures

crates/stdx/src/lib.rs

@@ -128,3 +128,85 @@ pub fn split_delim(haystack: &str, delim: char) -> Option<(&str, &str)> {
     let idx = haystack.find(delim)?;
     Some((&haystack[..idx], &haystack[idx + delim.len_utf8()..]))
 }
+
+pub fn trim_indent(mut text: &str) -> String {
+    if text.starts_with('\n') {
+        text = &text[1..];
+    }
+    let indent = text
+        .lines()
+        .filter(|it| !it.trim().is_empty())
+        .map(|it| it.len() - it.trim_start().len())
+        .min()
+        .unwrap_or(0);
+    lines_with_ends(text)
+        .map(
+            |line| {
+                if line.len() <= indent {
+                    line.trim_start_matches(' ')
+                } else {
+                    &line[indent..]
+                }
+            },
+        )
+        .collect()
+}
+
+pub fn lines_with_ends(text: &str) -> LinesWithEnds {
+    LinesWithEnds { text }
+}
+
+pub struct LinesWithEnds<'a> {
+    text: &'a str,
+}
+
+impl<'a> Iterator for LinesWithEnds<'a> {
+    type Item = &'a str;
+    fn next(&mut self) -> Option<&'a str> {
+        if self.text.is_empty() {
+            return None;
+        }
+        let idx = self.text.find('\n').map_or(self.text.len(), |it| it + 1);
+        let (res, next) = self.text.split_at(idx);
+        self.text = next;
+        Some(res)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_trim_indent() {
+        assert_eq!(trim_indent(""), "");
+        assert_eq!(
+            trim_indent(
+                "
+            hello
+            world
+"
+            ),
+            "hello\nworld\n"
+        );
+        assert_eq!(
+            trim_indent(
+                "
+            hello
+            world"
+            ),
+            "hello\nworld"
+        );
+        assert_eq!(trim_indent("    hello\n    world\n"), "hello\nworld\n");
+        assert_eq!(
+            trim_indent(
+                "
+            fn main() {
+                return 92;
+            }
+        "
+            ),
+            "fn main() {\n    return 92;\n}\n"
+        );
+    }
+}