Auto merge of #12289 - epage:basic, r=weihanglo

fix: Allow embedded manifests in all commands

### What does this PR try to resolve?

This is a part of #12207.

One of the goals is for embedded manifests to be a first class citizen.  If you have a script, you should be able to run tests on it, for example.

This expands the error check from just `Cargo.toml` to also single-file packages so you can use it in `--manifest-path`.

This, however, does mean that these *can* be used in places that likely won't work yet, like `cargo publish`.

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

By commit.  We introduce tests for basic commands and then implement and refine the support for this.

### Additional information

Other information you want to mention in this PR, such as prior arts,
future extensions, an unresolved problem, or a TODO list.

Author: bors

src/bin/cargo/commands/run.rs

@@ -85,6 +85,7 @@ pub fn exec(config: &mut Config, args: &ArgMatches) -> CliResult {
     ops::run(&ws, &compile_opts, &values_os(args, "args")).map_err(|err| to_run_error(config, err))
 }
 
+/// See also `util/toml/mod.rs`s `is_embedded`
 pub fn is_manifest_command(arg: &str) -> bool {
     let path = Path::new(arg);
     1 < path.components().count()
@@ -98,15 +99,7 @@ pub fn exec_manifest_command(config: &Config, cmd: &str, args: &[OsString]) -> C
     }
 
     let manifest_path = Path::new(cmd);
-    let manifest_path = config.cwd().join(manifest_path);
-    let manifest_path = cargo_util::paths::normalize_path(&manifest_path);
-    if !manifest_path.exists() {
-        return Err(anyhow::format_err!(
-            "manifest path `{}` does not exist",
-            manifest_path.display()
-        )
-        .into());
-    }
+    let manifest_path = root_manifest(Some(manifest_path), config)?;
     let mut ws = Workspace::new(&manifest_path, config)?;
     if config.cli_unstable().avoid_dev_deps {
         ws.set_require_optional_deps(false);

src/cargo/util/command_prelude.rs

@@ -15,6 +15,7 @@ use crate::CargoResult;
 use anyhow::bail;
 use cargo_util::paths;
 use std::ffi::{OsStr, OsString};
+use std::path::Path;
 use std::path::PathBuf;
 
 pub use crate::core::compiler::CompileMode;
@@ -339,22 +340,7 @@ pub trait ArgMatchesExt {
     }
 
     fn root_manifest(&self, config: &Config) -> CargoResult<PathBuf> {
-        if let Some(path) = self.value_of_path("manifest-path", config) {
-            // In general, we try to avoid normalizing paths in Cargo,
-            // but in this particular case we need it to fix #3586.
-            let path = paths::normalize_path(&path);
-            if !path.ends_with("Cargo.toml") {
-                anyhow::bail!("the manifest-path must be a path to a Cargo.toml file")
-            }
-            if !path.exists() {
-                anyhow::bail!(
-                    "manifest path `{}` does not exist",
-                    self._value_of("manifest-path").unwrap()
-                )
-            }
-            return Ok(path);
-        }
-        find_root_manifest_for_wd(config.cwd())
+        root_manifest(self._value_of("manifest-path").map(Path::new), config)
     }
 
     fn workspace<'a>(&self, config: &'a Config) -> CargoResult<Workspace<'a>> {
@@ -792,6 +778,33 @@ pub fn values_os(args: &ArgMatches, name: &str) -> Vec<OsString> {
     args._values_of_os(name)
 }
 
+pub fn root_manifest(manifest_path: Option<&Path>, config: &Config) -> CargoResult<PathBuf> {
+    if let Some(manifest_path) = manifest_path {
+        let path = config.cwd().join(manifest_path);
+        // In general, we try to avoid normalizing paths in Cargo,
+        // but in this particular case we need it to fix #3586.
+        let path = paths::normalize_path(&path);
+        if !path.ends_with("Cargo.toml") && !crate::util::toml::is_embedded(&path) {
+            anyhow::bail!("the manifest-path must be a path to a Cargo.toml file")
+        }
+        if !path.exists() {
+            anyhow::bail!("manifest path `{}` does not exist", manifest_path.display())
+        }
+        if path.is_dir() {
+            anyhow::bail!(
+                "manifest path `{}` is a directory but expected a file",
+                manifest_path.display()
+            )
+        }
+        if crate::util::toml::is_embedded(&path) && !config.cli_unstable().script {
+            anyhow::bail!("embedded manifest `{}` requires `-Zscript`", path.display())
+        }
+        Ok(path)
+    } else {
+        find_root_manifest_for_wd(config.cwd())
+    }
+}
+
 #[track_caller]
 pub fn ignore_unknown<T: Default>(r: Result<T, clap::parser::MatchesError>) -> T {
     match r {

src/cargo/util/toml/mod.rs

@@ -74,9 +74,12 @@ pub fn read_manifest(
         .map_err(|err| ManifestError::new(err, path.into()))
 }
 
-fn is_embedded(path: &Path) -> bool {
+/// See also `bin/cargo/commands/run.rs`s `is_manifest_command`
+pub fn is_embedded(path: &Path) -> bool {
     let ext = path.extension();
-    ext.is_none() || ext == Some(OsStr::new("rs"))
+    ext == Some(OsStr::new("rs")) ||
+        // Provide better errors by not considering directories to be embedded manifests
+        (ext.is_none() && path.is_file())
 }
 
 /// Parse an already-loaded `Cargo.toml` as a Cargo manifest.