fix(manifest): Show error source to users

Several parts of this are not ideal yet
- Frontmatter close should show the open and show the EOF, instead of
  pointing at the open
- Trailing content on close will usually have a newline
- Multiple frontmatters should show the original frontmatter
- Some content, like supported infostrings, should go in a help
- Ideally we try to recover on no closing and instead point out a
  mismatched open/close

But this is still an improvement over nothing!

Author: epage

src/cargo/util/toml/mod.rs

@@ -67,8 +67,7 @@ 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 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)
@@ -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)
 }
@@ -2777,6 +2777,31 @@ fn lints_to_rustflags(lints: &manifest::TomlLints) -> CargoResult<Vec<String>> {
     Ok(rustflags)
 }
 
+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,

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
+  | ^^^^