fix(frontmatter): Add more visible context to errors

Author: epage

src/cargo/util/frontmatter.rs

@@ -72,17 +72,18 @@ impl<'s> ScriptSource<'s> {
                     format!(
                         "found {fence_length} `{FENCE_CHAR}` in rust frontmatter, expected at least 3"
                     ),
-                    open_start..open_end,
-                ));
+                    raw.len()..raw.len(),
+                ).push_visible_span(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!("unclosed frontmatter; expected `{fence_pattern}`"),
-                open_start..open_end,
-            ));
+                raw.len()..raw.len(),
+            )
+            .push_visible_span(open_start..open_end));
         };
         let info = input.next_slice(info_nl.start);
         let info = info.trim_matches(is_whitespace);
@@ -109,12 +110,14 @@ impl<'s> ScriptSource<'s> {
                         "closing code fence has {fewer_dashes} less `-` than the opening fence"
                     ),
                     close_start..close_end,
-                ));
+                )
+                .push_visible_span(open_start..open_end));
             }
             return Err(FrontmatterError::new(
                 format!("unclosed frontmatter; expected `{fence_pattern}`"),
-                open_start..open_end,
-            ));
+                raw.len()..raw.len(),
+            )
+            .push_visible_span(open_start..open_end));
         };
         let frontmatter_start = input.current_token_start() + 1; // skip nl from infostring
         let _ = input.next_slice(frontmatter_nl.start + 1);
@@ -141,15 +144,17 @@ impl<'s> ScriptSource<'s> {
             return Err(FrontmatterError::new(
                 format!("closing code fence has {extra_dashes} more `-` than the opening fence"),
                 extra_start..extra_end,
-            ));
+            )
+            .push_visible_span(open_start..open_end));
         } else {
             let after_closing_fence = after_closing_fence.trim_matches(is_whitespace);
             if !after_closing_fence.is_empty() {
                 // extra characters beyond the original fence pattern
                 return Err(FrontmatterError::new(
                     format!("unexpected characters after frontmatter close"),
                     close_end..content_start,
-                ));
+                )
+                .push_visible_span(open_start..open_end));
             }
         }
 
@@ -169,7 +174,9 @@ impl<'s> ScriptSource<'s> {
             return Err(FrontmatterError::new(
                 format!("only one frontmatter is supported"),
                 fence_start..fence_end,
-            ));
+            )
+            .push_visible_span(open_start..open_end)
+            .push_visible_span(close_start..close_end));
         }
 
         Ok(source)
@@ -287,23 +294,34 @@ fn is_whitespace(c: char) -> bool {
 pub struct FrontmatterError {
     message: String,
     primary_span: Span,
+    visible_spans: Vec<Span>,
 }
 
 impl FrontmatterError {
     pub fn new(message: impl Into<String>, span: Span) -> Self {
         Self {
             message: message.into(),
             primary_span: span,
+            visible_spans: Vec::new(),
         }
     }
 
+    pub fn push_visible_span(mut self, span: Span) -> Self {
+        self.visible_spans.push(span);
+        self
+    }
+
     pub fn message(&self) -> &str {
         self.message.as_str()
     }
 
     pub fn primary_span(&self) -> Span {
         self.primary_span.clone()
     }
+
+    pub fn visible_spans(&self) -> &[Span] {
+        &self.visible_spans
+    }
 }
 
 impl std::fmt::Display for FrontmatterError {

src/cargo/util/toml/embedded.rs

@@ -11,18 +11,20 @@ pub(super) fn expand_manifest(content: &str) -> Result<String, FrontmatterError>
             Some("cargo") | None => {}
             Some(other) => {
                 let info_span = source.info_span().unwrap();
+                let close_span = source.close_span().unwrap();
                 if let Some(remainder) = other.strip_prefix("cargo,") {
                     return Err(FrontmatterError::new(
                         format!("unsupported frontmatter infostring attributes: `{remainder}`"),
                         info_span,
-                    ));
+                    )
+                    .push_visible_span(close_span));
                 } else {
                     return Err(FrontmatterError::new(
                         format!(
                             "unsupported frontmatter infostring `{other}`; specify `cargo` for embedding a manifest"
                         ),
                         info_span,
-                    ));
+                    ).push_visible_span(close_span));
                 }
             }
         }

src/cargo/util/toml/mod.rs

@@ -2793,7 +2793,12 @@ fn emit_frontmatter_diagnostic(
     let group = Group::with_title(Level::ERROR.primary_title(e.message())).element(
         Snippet::source(contents)
             .path(manifest_path)
-            .annotation(AnnotationKind::Primary.span(primary_span)),
+            .annotation(AnnotationKind::Primary.span(primary_span))
+            .annotations(
+                e.visible_spans()
+                    .iter()
+                    .map(|s| AnnotationKind::Visible.span(s.clone())),
+            ),
     );
 
     if let Err(err) = gctx.shell().print_report(&[group], true) {

tests/testsuite/script/rustc_fixtures/dot-in-infostring-leading.stderr

@@ -3,3 +3,6 @@
   |
 1 | ---.toml
   |    ^^^^^
+2 | //~^ ERROR: invalid infostring for frontmatter
+3 | ---
+  |

tests/testsuite/script/rustc_fixtures/dot-in-infostring-non-leading.stderr

@@ -3,3 +3,5 @@
   |
 1 | ---Cargo.toml
   |    ^^^^^^^^^^
+2 | ---
+  |

tests/testsuite/script/rustc_fixtures/extra-after-end.stderr

@@ -1,6 +1,7 @@
 [ERROR] unexpected characters after frontmatter close
  --> script:2:4
   |
+1 |   ---
 2 |   ---cargo
   |  ____^
 3 | | //~^ ERROR: extra characters after frontmatter close are not allowed

tests/testsuite/script/rustc_fixtures/frontmatter-whitespace-2.stderr

@@ -1,5 +1,7 @@
 [ERROR] unclosed frontmatter; expected `---`
- --> script:1:1
-  |
-1 | ---cargo
-  | ^^^
+  --> script:14:56
+   |
+ 1 | ---cargo
+...
+14 | // within them and get treated as a frontmatter close.
+   |                                                       ^

tests/testsuite/script/rustc_fixtures/hyphen-in-infostring-leading.stderr

@@ -3,3 +3,6 @@
   |
 1 | --- -toml
   |     ^^^^^
+2 | //~^ ERROR: invalid infostring for frontmatter
+3 | ---
+  |

tests/testsuite/script/rustc_fixtures/hyphen-in-infostring-non-leading.stderr

@@ -3,3 +3,5 @@
   |
 1 | --- Cargo-toml
   |     ^^^^^^^^^^
+2 | ---
+  |

tests/testsuite/script/rustc_fixtures/infostring-fail.stderr

@@ -3,3 +3,6 @@
   |
 1 | ---cargo,clippy
   |    ^^^^^^^^^^^^
+2 | //~^ ERROR: invalid infostring for frontmatter
+3 | ---
+  |