Add basic support for cargo metadata (#110)

The `cargo metadata` command outputs a lot of useful information about
the current package.

This will be helpful for the `build`, `run` and `bump` commands.

See the [`cargo metadata`
documentation](https://doc.rust-lang.org/cargo/commands/cargo-metadata.html)
for more info.

Note that with this PR, we don't support the full output yet, we can
incrementally add more things as we need them.

Cargo.toml

@@ -29,5 +29,9 @@ dialoguer = { version = "0.11.0", default-features = false }
 
 # API interaction
 serde = { features = ["derive"], version = "1.0.210" }
+serde_json = "1.0.128"
 reqwest = { features = ["blocking", "json"], version = "0.12.7" }
 regex = "1.10.6"
+
+# Understanding package versions
+semver = { version = "1.0.23", features = ["serde"] }

src/external_cli/cargo/metadata.rs

@@ -0,0 +1,146 @@
+use std::{ffi::OsStr, path::PathBuf, process::Command};
+
+use semver::{Version, VersionReq};
+use serde::Deserialize;
+
+use super::program;
+
+/// Create a command to run `cargo metadata`.
+pub(crate) fn command() -> Command {
+    let mut command = Command::new(program());
+    // The format version needs to be fixed for compatibility and to avoid a warning log
+    command.args(["metadata", "--format-version", "1"]);
+    command
+}
+
+/// Try to obtain the Cargo metadata of this pacakge.
+pub(crate) fn metadata() -> anyhow::Result<Metadata> {
+    metadata_with_args::<[&str; 0], &str>([])
+}
+
+/// Try to obtain the Cargo metadata of this pacakge.
+///
+/// To see which additional args are available, [consult the `cargo metadata` documentation](https://doc.rust-lang.org/cargo/commands/cargo-metadata.html)
+/// or use `cargo metadata --help`.
+pub(crate) fn metadata_with_args<I, S>(additional_args: I) -> anyhow::Result<Metadata>
+where
+    I: IntoIterator<Item = S>,
+    S: AsRef<OsStr>,
+{
+    let output = command().args(additional_args).output()?;
+    let metadata = serde_json::from_slice(&output.stdout)?;
+    Ok(metadata)
+}
+
+/// Metadata information about the current package.
+///
+/// See the [`cargo metadata` specification](https://doc.rust-lang.org/cargo/commands/cargo-metadata.html#json-format).
+#[derive(Debug, Deserialize)]
+pub struct Metadata {
+    /// List of all packages in the workspace.
+    ///
+    /// It also includes all feature-enabled dependencies unless `--no-deps` is used.
+    packages: Vec<Package>,
+    /// List of members of the workspace.
+    ///
+    /// Each entry is the Package ID for the package.
+    workspace_members: Option<Vec<String>>,
+    /// List of default members of the workspace.
+    ///
+    /// Each entry is the Package ID for the package.
+    workspace_default_members: Option<Vec<String>>,
+    /// The absolute path to the build directory where Cargo places its output.
+    target_directory: PathBuf,
+    /// The absolute path to the root of the workspace.
+    workspace_root: Option<PathBuf>,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct Package {
+    /// The name of the package.
+    name: String,
+    /// The version of the package.
+    version: Version,
+    /// The Package ID for referring to the package within the document and as the `--package`
+    /// argument to many commands.
+    id: String,
+    /// List of Cargo targets.
+    targets: Vec<Target>,
+    /// Absolute path to this package's manifest.
+    manifest_path: PathBuf,
+    /// Optional string that is the default binary picked by cargo run.
+    default_run: Option<String>,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct Dependency {
+    /// The name of the dependency.
+    name: String,
+    /// The version requirement for the dependency.
+    ///
+    /// Dependencies without a version requirement have a value of `*`.
+    #[serde(default)]
+    req: VersionReq,
+    /// The dependency kind.
+    ///
+    /// `"dev"`, `"build"`, or `null` for a normal dependency.
+    #[serde(default)]
+    kind: DependencyKind,
+    /// The file system path for a local path dependency.
+    ///
+    /// Not present if not a path dependency.
+    path: Option<PathBuf>,
+}
+
+#[derive(Debug, Deserialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum DependencyKind {
+    #[default]
+    Normal,
+    Dev,
+    Build,
+    #[serde(untagged)]
+    Unknown(String),
+}
+
+#[derive(Debug, Deserialize)]
+pub struct Target {
+    kind: Vec<TargetKind>,
+    /// The name of the target.
+    ///
+    /// For lib targets, dashes will be replaced with underscores.
+    name: String,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum TargetKind {
+    Lib,
+    Rlib,
+    Dylib,
+    ProcMacro,
+    Bin,
+    Example,
+    Test,
+    Bench,
+    CustomBuild,
+    #[serde(untagged)]
+    Unknown(String),
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn should_determine_metadata_of_this_package() {
+        let metadata = metadata();
+        assert!(metadata.is_ok());
+        let metadata = metadata.unwrap();
+
+        assert!(metadata
+            .packages
+            .iter()
+            .any(|package| package.name == "bevy_cli"));
+    }
+}

src/external_cli/cargo/mod.rs

@@ -6,6 +6,7 @@ use clap::{ArgAction, Args};
 use super::arg_builder::ArgBuilder;
 
 pub(crate) mod build;
+pub(crate) mod metadata;
 
 fn program() -> OsString {
     env::var_os("BEVY_CLI_CARGO").unwrap_or("cargo".into())