fix(manifest): Be more direct in infostring errors

Author: epage

src/cargo/util/toml/embedded.rs

@@ -12,15 +12,13 @@ pub(super) fn expand_manifest(content: &str) -> Result<String, FrontmatterError>
             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"
-                        ),
+                        format!("unsupported frontmatter infostring attributes: `{remainder}`"),
                         source.info_span().unwrap(),
                     ));
                 } else {
                     return Err(FrontmatterError::new(
                         format!(
-                            "frontmatter infostring `{other}` is unsupported by cargo; specify `cargo` for embedding a manifest"
+                            "unsupported frontmatter infostring `{other}`; specify `cargo` for embedding a manifest"
                         ),
                         source.info_span().unwrap(),
                     ));

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

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

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

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

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

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

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

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

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

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