Make cargo script ignore workspaces (#15496)

### What does this PR try to resolve?

Cargo script considers itself part of the workspace if the script is
located in a sub-directory of a workspace (presumably since
https://github.com/rust-lang/cargo/pull/15168). This becomes an issue
when using a custom registry that is defined in the `.cargo/config.toml`
within the workspace. Cargo script does not take that file into account
and fails with ``registry index was not found in any configuration:
`test-reg` ``.

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

This PR adds a regression test and makes cargo script ignore the
surrounding workspace.
The test ~~will fail without the fix in the second commit and~~ can be
used to reproduce the issue.

### Additional information

The issue started occurring with `nightly-2025-02-16`.
Related to https://github.com/rust-lang/cargo/issues/12207.

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src/cargo/util/toml/mod.rs

@@ -13,6 +13,7 @@ use cargo_platform::Platform;
 use cargo_util::paths;
 use cargo_util_schemas::manifest::{
     self, PackageName, PathBaseName, TomlDependency, TomlDetailedDependency, TomlManifest,
+    TomlWorkspace,
 };
 use cargo_util_schemas::manifest::{RustVersion, StringOrBool};
 use itertools::Itertools;
@@ -80,7 +81,8 @@ pub fn read_manifest(
         let empty = Vec::new();
         let cargo_features = original_toml.cargo_features.as_ref().unwrap_or(&empty);
         let features = Features::new(cargo_features, gctx, &mut warnings, source_id.is_path())?;
-        let workspace_config = to_workspace_config(&original_toml, path, gctx, &mut warnings)?;
+        let workspace_config =
+            to_workspace_config(&original_toml, path, is_embedded, gctx, &mut warnings)?;
         if let WorkspaceConfig::Root(ws_root_config) = &workspace_config {
             let package_root = path.parent().unwrap();
             gctx.ws_roots
@@ -211,9 +213,14 @@ fn stringify(dst: &mut String, path: &serde_ignored::Path<'_>) {
 fn to_workspace_config(
     original_toml: &manifest::TomlManifest,
     manifest_file: &Path,
+    is_embedded: bool,
     gctx: &GlobalContext,
     warnings: &mut Vec<String>,
 ) -> CargoResult<WorkspaceConfig> {
+    if is_embedded {
+        let ws_root_config = to_workspace_root_config(&TomlWorkspace::default(), manifest_file);
+        return Ok(WorkspaceConfig::Root(ws_root_config));
+    }
     let workspace_config = match (
         original_toml.workspace.as_ref(),
         original_toml.package().and_then(|p| p.workspace.as_ref()),

tests/testsuite/script.rs

@@ -1886,3 +1886,54 @@ CARGO_MANIFEST_PATH: [ROOT]/foo/script.rs
 "#]])
         .run();
 }
+
+#[cargo_test]
+fn ignore_surrounding_workspace() {
+    let p = cargo_test_support::project()
+        .file(
+            std::path::Path::new(".cargo").join("config.toml"),
+            r#"
+[registries.test-reg]
+index = "https://github.com/rust-lang/crates.io-index"
+"#,
+        )
+        .file(
+            std::path::Path::new("inner").join("Cargo.toml"),
+            r#"
+[package]
+name = "inner"
+version = "0.1.0"
+
+[dependencies]
+serde = { version = "1.0", registry = "test-reg" }
+"#,
+        )
+        .file(std::path::Path::new("inner").join("src").join("lib.rs"), "")
+        .file(std::path::Path::new("script").join("echo.rs"), ECHO_SCRIPT)
+        .file(
+            "Cargo.toml",
+            r#"
+[workspace]
+members = [
+    "inner",
+]
+"#,
+        )
+        .build();
+
+    p.cargo("-Zscript -v script/echo.rs")
+        .masquerade_as_nightly_cargo(&["script"])
+        .with_stdout_data(str![[r#"
+bin: [ROOT]/home/.cargo/target/[HASH]/debug/echo[EXE]
+args: []
+
+"#]])
+        .with_stderr_data(str![[r#"
+[WARNING] `package.edition` is unspecified, defaulting to `2024`
+[COMPILING] echo v0.0.0 ([ROOT]/foo/script/echo.rs)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[RUNNING] `[ROOT]/home/.cargo/target/[HASH]/debug/echo[EXE]`
+
+"#]])
+        .run();
+}