bevy_macro_utils/
bevy_manifest.rs

1extern crate proc_macro;
2
3use alloc::collections::BTreeMap;
4use proc_macro::TokenStream;
5use std::sync::{PoisonError, RwLock};
6use std::{
7    env,
8    path::{Path, PathBuf},
9    time::SystemTime,
10};
11use toml_edit::{Document, Item};
12
13/// The path to the `Cargo.toml` file for the Bevy project.
14#[derive(Debug)]
15pub struct BevyManifest {
16    manifest: Document<Box<str>>,
17    modified_time: SystemTime,
18}
19
20const BEVY: &str = "bevy";
21
22impl BevyManifest {
23    /// Calls `f` with a global shared instance of the [`BevyManifest`] struct.
24    pub fn shared<R>(f: impl FnOnce(&BevyManifest) -> R) -> R {
25        static MANIFESTS: RwLock<BTreeMap<PathBuf, BevyManifest>> = RwLock::new(BTreeMap::new());
26        let manifest_path = Self::get_manifest_path();
27        let modified_time = Self::get_manifest_modified_time(&manifest_path)
28            .expect("The Cargo.toml should have a modified time");
29
30        let manifests = MANIFESTS.read().unwrap_or_else(PoisonError::into_inner);
31        if let Some(manifest) = manifests.get(&manifest_path)
32            && manifest.modified_time == modified_time
33        {
34            return f(manifest);
35        }
36
37        drop(manifests);
38
39        let manifest = BevyManifest {
40            manifest: Self::read_manifest(&manifest_path),
41            modified_time,
42        };
43
44        let key = manifest_path.clone();
45        // TODO: Switch to using RwLockWriteGuard::downgrade when it stabilizes.
46        MANIFESTS
47            .write()
48            .unwrap_or_else(PoisonError::into_inner)
49            .insert(key, manifest);
50
51        f(MANIFESTS
52            .read()
53            .unwrap_or_else(PoisonError::into_inner)
54            .get(&manifest_path)
55            .unwrap())
56    }
57
58    fn get_manifest_path() -> PathBuf {
59        env::var_os("CARGO_MANIFEST_DIR")
60            .map(|path| {
61                let mut path = PathBuf::from(path);
62                path.push("Cargo.toml");
63                assert!(
64                    path.exists(),
65                    "Cargo manifest does not exist at path {}",
66                    path.display()
67                );
68                path
69            })
70            .expect("CARGO_MANIFEST_DIR is not defined.")
71    }
72
73    fn get_manifest_modified_time(
74        cargo_manifest_path: &Path,
75    ) -> Result<SystemTime, std::io::Error> {
76        std::fs::metadata(cargo_manifest_path).and_then(|metadata| metadata.modified())
77    }
78
79    fn read_manifest(path: &Path) -> Document<Box<str>> {
80        let manifest = std::fs::read_to_string(path)
81            .unwrap_or_else(|_| panic!("Unable to read cargo manifest: {}", path.display()))
82            .into_boxed_str();
83        Document::parse(manifest)
84            .unwrap_or_else(|_| panic!("Failed to parse cargo manifest: {}", path.display()))
85    }
86
87    /// Attempt to retrieve the [path](syn::Path) of a particular package in
88    /// the [manifest](BevyManifest) by [name](str).
89    pub fn maybe_get_path(&self, name: &str) -> Option<syn::Path> {
90        let find_in_deps = |deps: &Item| -> Option<syn::Path> {
91            let package = if deps.get(name).is_some() {
92                return Some(Self::parse_str(name));
93            } else if deps.get(BEVY).is_some() {
94                BEVY
95            } else {
96                // Note: to support bevy crate aliases, we could do scanning here to find a crate with a "package" name that
97                // matches our request, but that would then mean we are scanning every dependency (and dev dependency) for every
98                // macro execution that hits this branch (which includes all built-in bevy crates). Our current stance is that supporting
99                // remapped crate names in derive macros is not worth that "compile time" price of admission. As a workaround, people aliasing
100                // bevy crate names can use "use REMAPPED as bevy_X" or "use REMAPPED::x as bevy_x".
101                return None;
102            };
103
104            let mut path = Self::parse_str::<syn::Path>(&format!("::{package}"));
105            if let Some(module) = name.strip_prefix("bevy_") {
106                path.segments.push(Self::parse_str(module));
107            }
108            Some(path)
109        };
110
111        let deps = self.manifest.get("dependencies");
112        let deps_dev = self.manifest.get("dev-dependencies");
113
114        deps.and_then(find_in_deps)
115            .or_else(|| deps_dev.and_then(find_in_deps))
116    }
117
118    /// Attempt to parse the provided [path](str) as a [syntax tree node](syn::parse::Parse)
119    pub fn try_parse_str<T: syn::parse::Parse>(path: &str) -> Option<T> {
120        syn::parse(path.parse::<TokenStream>().ok()?).ok()
121    }
122
123    /// Returns the path for the crate with the given name.
124    pub fn get_path(&self, name: &str) -> syn::Path {
125        self.maybe_get_path(name)
126            .unwrap_or_else(|| Self::parse_str(name))
127    }
128
129    /// Attempt to parse provided [path](str) as a [syntax tree node](syn::parse::Parse).
130    ///
131    /// # Panics
132    ///
133    /// Will panic if the path is not able to be parsed. For a non-panicking option, see [`try_parse_str`]
134    ///
135    /// [`try_parse_str`]: Self::try_parse_str
136    pub fn parse_str<T: syn::parse::Parse>(path: &str) -> T {
137        Self::try_parse_str(path).unwrap()
138    }
139}
bevy_macro_utils/bevy_manifest.rs

bevy_macro_utils/
bevy_manifest.rs
