refactor(frontmatter): Track spans for errors

Author: epage

src/cargo/util/frontmatter.rs

@@ -68,17 +68,21 @@ impl<'s> ScriptSource<'s> {
             }
             1 | 2 => {
                 // either not a frontmatter or invalid frontmatter opening
-                return Err(FrontmatterError::new(format!(
-                    "found {fence_length} `{FENCE_CHAR}` in rust frontmatter, expected at least 3"
-                )));
+                return Err(FrontmatterError::new(
+                    format!(
+                        "found {fence_length} `{FENCE_CHAR}` in rust frontmatter, expected at least 3"
+                    ),
+                    open_start..open_end,
+                ));
             }
             _ => {}
         }
         source.open = Some(open_start..open_end);
         let Some(info_nl) = input.find_slice("\n") else {
-            return Err(FrontmatterError::new(format!(
-                "no closing `{fence_pattern}` found for frontmatter"
-            )));
+            return Err(FrontmatterError::new(
+                format!("no closing `{fence_pattern}` found for frontmatter"),
+                open_start..open_end,
+            ));
         };
         let info = input.next_slice(info_nl.start);
         let info = info.trim_matches(is_whitespace);
@@ -91,9 +95,10 @@ impl<'s> ScriptSource<'s> {
         // Ends with a line that starts with a matching number of `-` only followed by whitespace
         let nl_fence_pattern = format!("\n{fence_pattern}");
         let Some(frontmatter_nl) = input.find_slice(nl_fence_pattern.as_str()) else {
-            return Err(FrontmatterError::new(format!(
-                "no closing `{fence_pattern}` found for frontmatter"
-            )));
+            return Err(FrontmatterError::new(
+                format!("no closing `{fence_pattern}` found for frontmatter"),
+                open_start..open_end,
+            ));
         };
         let frontmatter_start = input.current_token_start() + 1; // skip nl from infostring
         let _ = input.next_slice(frontmatter_nl.start + 1);
@@ -113,9 +118,10 @@ impl<'s> ScriptSource<'s> {
         let after_closing_fence = after_closing_fence.trim_matches(is_whitespace);
         if !after_closing_fence.is_empty() {
             // extra characters beyond the original fence pattern, even if they are extra `-`
-            return Err(FrontmatterError::new(format!(
-                "trailing characters found after frontmatter close"
-            )));
+            return Err(FrontmatterError::new(
+                format!("trailing characters found after frontmatter close"),
+                close_end..content_start,
+            ));
         }
 
         source.content = content_start..content_end;
@@ -129,9 +135,12 @@ impl<'s> ScriptSource<'s> {
             .find_map(|(i, c)| (c != FENCE_CHAR).then_some(i))
             .unwrap_or_else(|| input.eof_offset());
         if 0 < fence_length {
-            return Err(FrontmatterError::new(format!(
-                "only one frontmatter is supported"
-            )));
+            let fence_start = input.current_token_start();
+            let fence_end = fence_start + fence_length;
+            return Err(FrontmatterError::new(
+                format!("only one frontmatter is supported"),
+                fence_start..fence_end,
+            ));
         }
 
         Ok(source)
@@ -248,14 +257,24 @@ fn is_whitespace(c: char) -> bool {
 #[derive(Debug)]
 pub struct FrontmatterError {
     message: String,
+    span: Span,
 }
 
 impl FrontmatterError {
-    pub fn new(message: impl Into<String>) -> Self {
+    pub fn new(message: impl Into<String>, span: Span) -> Self {
         Self {
             message: message.into(),
+            span,
         }
     }
+
+    pub fn message(&self) -> &str {
+        self.message.as_str()
+    }
+
+    pub fn span(&self) -> Span {
+        self.span.clone()
+    }
 }
 
 impl std::fmt::Display for FrontmatterError {

src/cargo/util/toml/embedded.rs

@@ -11,13 +11,19 @@ pub(super) fn expand_manifest(content: &str) -> Result<String, FrontmatterError>
             Some("cargo") | None => {}
             Some(other) => {
                 if let Some(remainder) = other.strip_prefix("cargo,") {
-                    return Err(FrontmatterError::new(format!(
-                        "cargo does not support frontmatter infostring attributes like `{remainder}` at this time"
-                    )));
+                    return Err(FrontmatterError::new(
+                        format!(
+                            "cargo does not support frontmatter infostring attributes like `{remainder}` at this time"
+                        ),
+                        source.info_span().unwrap(),
+                    ));
                 } else {
-                    return Err(FrontmatterError::new(format!(
-                        "frontmatter infostring `{other}` is unsupported by cargo; specify `cargo` for embedding a manifest"
-                    )));
+                    return Err(FrontmatterError::new(
+                        format!(
+                            "frontmatter infostring `{other}` is unsupported by cargo; specify `cargo` for embedding a manifest"
+                        ),
+                        source.info_span().unwrap(),
+                    ));
                 }
             }
         }