Revert "feat(embedded): Add prefix-char frontmatter syntax support"

This reverts commit b77ce7fa292622c5482047ee428c1ead1f4c3643.

src/cargo/util/toml/embedded.rs

@@ -185,7 +185,7 @@ fn sanitize_name(name: &str) -> String {
 struct Source<'s> {
     shebang: Option<&'s str>,
     info: Option<&'s str>,
-    frontmatter: Option<String>,
+    frontmatter: Option<&'s str>,
     content: &'s str,
 }
 
@@ -234,14 +234,11 @@ fn split_source(input: &str) -> CargoResult<Source<'_>> {
         0 => {
             return Ok(source);
         }
-        1 if tick_char == '#' => {
-            // Attribute
-            return Ok(source);
-        }
-        2 if tick_char == '#' => {
-            return split_prefix_source(source, "##");
-        }
         1 | 2 => {
+            if tick_char == '#' {
+                // Attribute
+                return Ok(source);
+            }
             anyhow::bail!("found {tick_end} `{tick_char}` in rust frontmatter, expected at least 3")
         }
         _ => source.content.split_at(tick_end),
@@ -255,7 +252,7 @@ fn split_source(input: &str) -> CargoResult<Source<'_>> {
     let Some((frontmatter, content)) = source.content.split_once(fence_pattern) else {
         anyhow::bail!("no closing `{fence_pattern}` found for frontmatter");
     };
-    source.frontmatter = Some(frontmatter.to_owned());
+    source.frontmatter = Some(frontmatter);
     source.content = content;
 
     let (line, content) = source
@@ -271,22 +268,6 @@ fn split_source(input: &str) -> CargoResult<Source<'_>> {
     Ok(source)
 }
 
-fn split_prefix_source<'s>(mut source: Source<'s>, prefix: &str) -> CargoResult<Source<'s>> {
-    let mut frontmatter = String::new();
-    while let Some(rest) = source.content.strip_prefix(prefix) {
-        if !rest.is_empty() && !rest.starts_with(' ') {
-            anyhow::bail!("frontmatter must have a space between `##` and the content");
-        }
-        let (line, rest) = rest.split_once('\n').unwrap_or((rest, ""));
-        frontmatter.push_str("  ");
-        frontmatter.push_str(line);
-        frontmatter.push('\n');
-        source.content = rest;
-    }
-    source.frontmatter = Some(frontmatter);
-    Ok(source)
-}
-
 #[cfg(test)]
 mod test_expand {
     use super::*;
@@ -394,7 +375,7 @@ fn main() {}
     }
 
     #[test]
-    fn test_dash_fence() {
+    fn test_dash() {
         snapbox::assert_matches(
             r#"[[bin]]
 name = "test-"
@@ -427,7 +408,7 @@ fn main() {}
     }
 
     #[test]
-    fn test_hash_fence() {
+    fn test_hash() {
         snapbox::assert_matches(
             r#"[[bin]]
 name = "test-"
@@ -455,37 +436,6 @@ strip = true
 time="0.1.25"
 ###
 fn main() {}
-"#),
-        );
-    }
-
-    #[test]
-    fn test_hash_prefix() {
-        snapbox::assert_matches(
-            r#"[[bin]]
-name = "test-"
-path = [..]
-
-[dependencies]
-time = "0.1.25"
-
-[package]
-autobenches = false
-autobins = false
-autoexamples = false
-autotests = false
-build = false
-edition = "2021"
-name = "test-"
-
-[profile.release]
-strip = true
-
-[workspace]
-"#,
-            si!(r#"## [dependencies]
-## time="0.1.25"
-fn main() {}
 "#),
         );
     }