fix(manifest): Show error source to users

src/cargo/util/frontmatter.rs

@@ -1,5 +1,3 @@
-use crate::CargoResult;
-
 type Span = std::ops::Range<usize>;
 
 #[derive(Debug)]
@@ -22,7 +20,7 @@ pub struct ScriptSource<'s> {
 }
 
 impl<'s> ScriptSource<'s> {
-    pub fn parse(raw: &'s str) -> CargoResult<Self> {
+    pub fn parse(raw: &'s str) -> Result<Self, FrontmatterError> {
         use winnow::stream::FindSlice as _;
         use winnow::stream::Location as _;
         use winnow::stream::Offset as _;
@@ -61,24 +59,30 @@ impl<'s> ScriptSource<'s> {
             .char_indices()
             .find_map(|(i, c)| (c != FENCE_CHAR).then_some(i))
             .unwrap_or_else(|| input.eof_offset());
+        let open_start = input.current_token_start();
+        let fence_pattern = input.next_slice(fence_length);
+        let open_end = input.current_token_start();
         match fence_length {
             0 => {
                 return Ok(source);
             }
             1 | 2 => {
                 // either not a frontmatter or invalid frontmatter opening
-                anyhow::bail!(
-                    "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,
+                ));
             }
             _ => {}
         }
-        let open_start = input.current_token_start();
-        let fence_pattern = input.next_slice(fence_length);
-        let open_end = input.current_token_start();
         source.open = Some(open_start..open_end);
         let Some(info_nl) = input.find_slice("\n") else {
-            anyhow::bail!("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);
@@ -91,7 +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 {
-            anyhow::bail!("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);
@@ -111,14 +118,29 @@ 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 `-`
-            anyhow::bail!("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;
 
-        let repeat = Self::parse(source.content())?;
-        if repeat.frontmatter.is_some() {
-            anyhow::bail!("only one frontmatter is supported");
+        if let Some(nl_end) = strip_ws_lines(input.as_ref()) {
+            let _ = input.next_slice(nl_end);
+        }
+        let fence_length = input
+            .as_ref()
+            .char_indices()
+            .find_map(|(i, c)| (c != FENCE_CHAR).then_some(i))
+            .unwrap_or_else(|| input.eof_offset());
+        if 0 < fence_length {
+            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)
@@ -232,6 +254,37 @@ fn is_whitespace(c: char) -> bool {
     )
 }
 
+#[derive(Debug)]
+pub struct FrontmatterError {
+    message: String,
+    span: Span,
+}
+
+impl FrontmatterError {
+    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 {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.message.fmt(fmt)
+    }
+}
+
+impl std::error::Error for FrontmatterError {}
+
 #[cfg(test)]
 mod test {
     use snapbox::assert_data_eq;

src/cargo/util/toml/embedded.rs

@@ -1,23 +1,29 @@
 use cargo_util_schemas::manifest::PackageName;
 
-use crate::CargoResult;
+use crate::util::frontmatter::FrontmatterError;
 use crate::util::frontmatter::ScriptSource;
 use crate::util::restricted_names;
 
-pub(super) fn expand_manifest(content: &str) -> CargoResult<String> {
+pub(super) fn expand_manifest(content: &str) -> Result<String, FrontmatterError> {
     let source = ScriptSource::parse(content)?;
     if let Some(span) = source.frontmatter_span() {
         match source.info() {
             Some("cargo") | None => {}
             Some(other) => {
                 if let Some(remainder) = other.strip_prefix("cargo,") {
-                    anyhow::bail!(
-                        "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 {
-                    anyhow::bail!(
-                        "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(),
+                    ));
                 }
             }
         }

src/cargo/util/toml/mod.rs

@@ -67,12 +67,11 @@ pub fn read_manifest(
     let mut errors = Default::default();
 
     let is_embedded = is_embedded(path);
-    let contents = read_toml_string(path, is_embedded, gctx)
-        .map_err(|err| ManifestError::new(err, path.into()))?;
-    let document =
-        parse_document(&contents).map_err(|e| emit_diagnostic(e.into(), &contents, path, gctx))?;
+    let contents = read_toml_string(path, is_embedded, gctx)?;
+    let document = parse_document(&contents)
+        .map_err(|e| emit_toml_diagnostic(e.into(), &contents, path, gctx))?;
     let original_toml = deserialize_toml(&document)
-        .map_err(|e| emit_diagnostic(e.into(), &contents, path, gctx))?;
+        .map_err(|e| emit_toml_diagnostic(e.into(), &contents, path, gctx))?;
 
     let mut manifest = (|| {
         let empty = Vec::new();
@@ -152,12 +151,13 @@ pub fn read_manifest(
 
 #[tracing::instrument(skip_all)]
 fn read_toml_string(path: &Path, is_embedded: bool, gctx: &GlobalContext) -> CargoResult<String> {
-    let mut contents = paths::read(path)?;
+    let mut contents = paths::read(path).map_err(|err| ManifestError::new(err, path.into()))?;
     if is_embedded {
         if !gctx.cli_unstable().script {
             anyhow::bail!("parsing `{}` requires `-Zscript`", path.display());
         }
-        contents = embedded::expand_manifest(&contents)?;
+        contents = embedded::expand_manifest(&contents)
+            .map_err(|e| emit_frontmatter_diagnostic(e, &contents, path, gctx))?;
     }
     Ok(contents)
 }
@@ -2777,7 +2777,32 @@ fn lints_to_rustflags(lints: &manifest::TomlLints) -> CargoResult<Vec<String>> {
     Ok(rustflags)
 }
 
-fn emit_diagnostic(
+fn emit_frontmatter_diagnostic(
+    e: crate::util::frontmatter::FrontmatterError,
+    contents: &str,
+    manifest_file: &Path,
+    gctx: &GlobalContext,
+) -> anyhow::Error {
+    let span = e.span();
+
+    // Get the path to the manifest, relative to the cwd
+    let manifest_path = diff_paths(manifest_file, gctx.cwd())
+        .unwrap_or_else(|| manifest_file.to_path_buf())
+        .display()
+        .to_string();
+    let group = Group::with_title(Level::ERROR.primary_title(e.message())).element(
+        Snippet::source(contents)
+            .path(manifest_path)
+            .annotation(AnnotationKind::Primary.span(span)),
+    );
+
+    if let Err(err) = gctx.shell().print_report(&[group], true) {
+        return err.into();
+    }
+    return AlreadyPrintedError::new(e.into()).into();
+}
+
+fn emit_toml_diagnostic(
     e: toml::de::Error,
     contents: &str,
     manifest_file: &Path,

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

@@ -1 +1,5 @@
 [ERROR] frontmatter infostring `.toml` is unsupported by cargo; specify `cargo` for embedding a manifest
+ --> script:1:4
+  |
+1 | ---.toml
+  |    ^^^^^

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

@@ -1 +1,5 @@
 [ERROR] frontmatter infostring `Cargo.toml` is unsupported by cargo; specify `cargo` for embedding a manifest
+ --> script:1:4
+  |
+1 | ---Cargo.toml
+  |    ^^^^^^^^^^

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

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

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

@@ -1 +1,5 @@
 [ERROR] no closing `---` found for frontmatter
+ --> script:1:1
+  |
+1 | ---cargo
+  | ^^^

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

@@ -1 +1,5 @@
 [ERROR] frontmatter infostring `-toml` is unsupported by cargo; specify `cargo` for embedding a manifest
+ --> script:1:5
+  |
+1 | --- -toml
+  |     ^^^^^

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

@@ -1 +1,5 @@
 [ERROR] frontmatter infostring `Cargo-toml` is unsupported by cargo; specify `cargo` for embedding a manifest
+ --> script:1:5
+  |
+1 | --- Cargo-toml
+  |     ^^^^^^^^^^

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

@@ -1 +1,5 @@
 [ERROR] cargo does not support frontmatter infostring attributes like `clippy` at this time
+ --> script:1:4
+  |
+1 | ---cargo,clippy
+  |    ^^^^^^^^^^^^

tests/testsuite/script/rustc_fixtures/mismatch-1.stderr

@@ -1 +1,7 @@
 [ERROR] trailing characters found after frontmatter close
+ --> script:3:4
+  |
+3 |   ----
+  |  ____^
+4 | |
+  | |_^

tests/testsuite/script/rustc_fixtures/mismatch-2.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^

tests/testsuite/script/rustc_fixtures/multifrontmatter.stderr

@@ -1 +1,5 @@
 [ERROR] only one frontmatter is supported
+ --> script:4:1
+  |
+4 | ---
+  | ^^^

tests/testsuite/script/rustc_fixtures/unclosed-1.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^

tests/testsuite/script/rustc_fixtures/unclosed-2.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^

tests/testsuite/script/rustc_fixtures/unclosed-3.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^

tests/testsuite/script/rustc_fixtures/unclosed-4.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^

tests/testsuite/script/rustc_fixtures/unclosed-5.stderr

@@ -1 +1,5 @@
 [ERROR] no closing `----` found for frontmatter
+ --> script:1:1
+  |
+1 | ----cargo
+  | ^^^^