fix(toml): Remove workaround for rustc frontmatter support (#15570)

### What does this PR try to resolve?

With rust-lang/rust#140035 now merged, we can rely on that rather than
dirty hacks

This is part of #12207

### How should we test and review this PR?

### Additional information

Author: weihanglo

src/cargo/core/compiler/mod.rs

@@ -735,6 +735,15 @@ fn prepare_rustc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResult
         .compilation
         .rustc_process(unit, is_primary, is_workspace)?;
     build_base_args(build_runner, &mut base, unit)?;
+    if unit.pkg.manifest().is_embedded() {
+        if !gctx.cli_unstable().script {
+            anyhow::bail!(
+                "parsing `{}` requires `-Zscript`",
+                unit.pkg.manifest_path().display()
+            );
+        }
+        base.arg("-Z").arg("crate-attr=feature(frontmatter)");
+    }
 
     base.inherit_jobserver(&build_runner.jobserver);
     build_deps_args(&mut base, build_runner, unit)?;
@@ -774,6 +783,15 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
     let bcx = build_runner.bcx;
     // script_metadata is not needed here, it is only for tests.
     let mut rustdoc = build_runner.compilation.rustdoc_process(unit, None)?;
+    if unit.pkg.manifest().is_embedded() {
+        if !bcx.gctx.cli_unstable().script {
+            anyhow::bail!(
+                "parsing `{}` requires `-Zscript`",
+                unit.pkg.manifest_path().display()
+            );
+        }
+        rustdoc.arg("-Z").arg("crate-attr=feature(frontmatter)");
+    }
     rustdoc.inherit_jobserver(&build_runner.jobserver);
     let crate_name = unit.target.crate_name();
     rustdoc.arg("--crate-name").arg(&crate_name);

src/cargo/util/toml/embedded.rs

@@ -1,16 +1,9 @@
-use anyhow::Context as _;
-
 use cargo_util_schemas::manifest::PackageName;
 
 use crate::util::restricted_names;
 use crate::CargoResult;
-use crate::GlobalContext;
 
-pub(super) fn expand_manifest(
-    content: &str,
-    path: &std::path::Path,
-    gctx: &GlobalContext,
-) -> CargoResult<String> {
+pub(super) fn expand_manifest(content: &str) -> CargoResult<String> {
     let source = ScriptSource::parse(content)?;
     if let Some(frontmatter) = source.frontmatter() {
         match source.info() {
@@ -24,74 +17,13 @@ pub(super) fn expand_manifest(
             }
         }
 
-        // HACK: until rustc has native support for this syntax, we have to remove it from the
-        // source file
-        use std::fmt::Write as _;
-        let hash = crate::util::hex::short_hash(&path.to_string_lossy());
-        let mut rel_path = std::path::PathBuf::new();
-        rel_path.push("target");
-        rel_path.push(&hash[0..2]);
-        rel_path.push(&hash[2..]);
-        let target_dir = gctx.home().join(rel_path);
-        let hacked_path = target_dir
-            .join(
-                path.file_name()
-                    .expect("always a name for embedded manifests"),
-            )
-            .into_path_unlocked();
-        let mut hacked_source = String::new();
-        if let Some(shebang) = source.shebang() {
-            writeln!(hacked_source, "{shebang}")?;
-        }
-        writeln!(hacked_source)?; // open
-        for _ in 0..frontmatter.lines().count() {
-            writeln!(hacked_source)?;
-        }
-        writeln!(hacked_source)?; // close
-        writeln!(hacked_source, "{}", source.content())?;
-        if let Some(parent) = hacked_path.parent() {
-            cargo_util::paths::create_dir_all(parent)?;
-        }
-        cargo_util::paths::write_if_changed(&hacked_path, hacked_source)?;
-
-        let manifest = inject_bin_path(&frontmatter, &hacked_path)
-            .with_context(|| format!("failed to parse manifest at `{}`", path.display()))?;
-        let manifest = toml::to_string_pretty(&manifest)?;
-        Ok(manifest)
+        Ok(frontmatter.to_owned())
     } else {
         let frontmatter = "";
-        let manifest = inject_bin_path(frontmatter, path)
-            .with_context(|| format!("failed to parse manifest at `{}`", path.display()))?;
-        let manifest = toml::to_string_pretty(&manifest)?;
-        Ok(manifest)
+        Ok(frontmatter.to_owned())
     }
 }
 
-/// HACK: Add a `[[bin]]` table to the `original_toml`
-fn inject_bin_path(manifest: &str, path: &std::path::Path) -> CargoResult<toml::Table> {
-    let mut manifest: toml::Table = toml::from_str(&manifest)?;
-
-    let bin_path = path.to_string_lossy().into_owned();
-    let file_stem = path
-        .file_stem()
-        .ok_or_else(|| anyhow::format_err!("no file name"))?
-        .to_string_lossy();
-    let name = sanitize_name(file_stem.as_ref());
-    let bin_name = name.clone();
-
-    let mut bin = toml::Table::new();
-    bin.insert("name".to_owned(), toml::Value::String(bin_name));
-    bin.insert("path".to_owned(), toml::Value::String(bin_path));
-    manifest
-        .entry("bin")
-        .or_insert_with(|| Vec::<toml::Value>::new().into())
-        .as_array_mut()
-        .ok_or_else(|| anyhow::format_err!("`bin` must be an array"))?
-        .push(toml::Value::Table(bin));
-
-    Ok(manifest)
-}
-
 /// Ensure the package name matches the validation from `ops::cargo_new::check_name`
 pub fn sanitize_name(name: &str) -> String {
     let placeholder = if name.contains('_') {
@@ -584,25 +516,12 @@ fn main() {}
 
     #[track_caller]
     fn expand(source: &str) -> String {
-        let shell = crate::Shell::from_write(Box::new(Vec::new()));
-        let cwd = std::env::current_dir().unwrap();
-        let home = home::cargo_home_with_cwd(&cwd).unwrap();
-        let gctx = GlobalContext::new(shell, cwd, home);
-        expand_manifest(source, std::path::Path::new("/home/me/test.rs"), &gctx)
-            .unwrap_or_else(|err| panic!("{}", err))
+        expand_manifest(source).unwrap_or_else(|err| panic!("{}", err))
     }
 
     #[test]
     fn expand_default() {
-        assert_data_eq!(
-            expand(r#"fn main() {}"#),
-            str![[r#"
-[[bin]]
-name = "test-"
-path = "/home/me/test.rs"
-
-"#]]
-        );
+        assert_data_eq!(expand(r#"fn main() {}"#), str![""]);
     }
 
     #[test]
@@ -617,12 +536,8 @@ fn main() {}
 "#
             ),
             str![[r#"
-[[bin]]
-name = "test-"
-path = [..]
-
 [dependencies]
-time = "0.1.25"
+time="0.1.25"
 
 "#]]
         );

src/cargo/util/toml/mod.rs

@@ -160,7 +160,7 @@ fn read_toml_string(path: &Path, is_embedded: bool, gctx: &GlobalContext) -> Car
         if !gctx.cli_unstable().script {
             anyhow::bail!("parsing `{}` requires `-Zscript`", path.display());
         }
-        contents = embedded::expand_manifest(&contents, path, gctx)?;
+        contents = embedded::expand_manifest(&contents)?;
     }
     Ok(contents)
 }
@@ -368,8 +368,37 @@ fn normalize_toml(
             original_package.autolib.or(auto_embedded),
             warnings,
         )?;
+        let original_toml_bin = if is_embedded {
+            let manifest_file_stem = manifest_file
+                .file_stem()
+                .expect("file name enforced previously");
+            let name = embedded::sanitize_name(manifest_file_stem.to_string_lossy().as_ref());
+            let manifest_file_name = manifest_file
+                .file_name()
+                .expect("file name enforced previously");
+            let path = PathBuf::from(manifest_file_name);
+            Cow::Owned(Some(vec![manifest::TomlBinTarget {
+                name: Some(name),
+                crate_type: None,
+                crate_type2: None,
+                path: Some(manifest::PathValue(path)),
+                filename: None,
+                test: None,
+                doctest: None,
+                bench: None,
+                doc: None,
+                doc_scrape_examples: None,
+                proc_macro: None,
+                proc_macro2: None,
+                harness: None,
+                required_features: None,
+                edition: None,
+            }]))
+        } else {
+            Cow::Borrowed(&original_toml.bin)
+        };
         normalized_toml.bin = Some(targets::normalize_bins(
-            original_toml.bin.as_ref(),
+            original_toml_bin.as_ref().as_ref(),
             package_root,
             package_name,
             edition,
@@ -1345,10 +1374,7 @@ pub fn to_real_manifest(
         let invalid_fields = [
             ("`workspace`", original_toml.workspace.is_some()),
             ("`lib`", original_toml.lib.is_some()),
-            (
-                "`bin`",
-                original_toml.bin.as_ref().map(|b| b.len()).unwrap_or(0) != 1,
-            ),
+            ("`bin`", original_toml.bin.is_some()),
             ("`example`", original_toml.example.is_some()),
             ("`test`", original_toml.test.is_some()),
             ("`bench`", original_toml.bench.is_some()),

tests/testsuite/fix.rs

@@ -2542,7 +2542,7 @@ edition = "2021"
     );
 }
 
-#[cargo_test]
+#[cargo_test(nightly, reason = "-Zscript is unstable")]
 fn migrate_removes_project_for_script() {
     let p = project()
         .file(
@@ -2576,7 +2576,7 @@ fn main() {
 [MIGRATING] foo.rs from 2021 edition to 2024
 [FIXED] foo.rs (1 fix)
 [CHECKING] foo v0.0.0 ([ROOT]/foo/foo.rs)
-[MIGRATING] [ROOT]/home/.cargo/target/[HASH]/foo.rs from 2021 edition to 2024
+[MIGRATING] foo.rs from 2021 edition to 2024
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
 "#]])

tests/testsuite/lockfile_path.rs

@@ -494,7 +494,7 @@ fn install_lock_file_path_must_present() {
         .run();
 }
 
-#[cargo_test]
+#[cargo_test(nightly, reason = "-Zscript is unstable")]
 fn run_embed() {
     let lockfile_path = "mylockfile/Cargo.lock";
     let invalid_lockfile = "Cargo.lock";

tests/testsuite/open_namespaces.rs

@@ -259,7 +259,7 @@ fn explicit_bin_within_namespace() {
         .run();
 }
 
-#[cargo_test]
+#[cargo_test(nightly, reason = "-Zscript is unstable")]
 #[cfg(unix)]
 fn namespaced_script_name() {
     let p = cargo_test_support::project()
@@ -314,7 +314,7 @@ fn main() {}
         "bin"
       ],
       "name": "foo::bar",
-      "src_path": "[ROOT]/home/.cargo/target/[HASH]/foo::bar.rs",
+      "src_path": "[ROOT]/foo/foo::bar.rs",
       "test": true
     }
   ],