Add prefer-index feature (#47)

* Add additional bug

* Add support for retrieving features via index

* Fix lint

* Fix deny

Cargo.toml

@@ -18,6 +18,8 @@ exclude = [".github", "tests"]
 
 [features]
 default = []
+# Uses the index as the source of truth for what features are available for a crate
+prefer-index = ["crates-index"]
 # Adds support for filtering target specific dependencies
 targets = ["cfg-expr/targets"]
 #features = []
@@ -27,6 +29,10 @@ targets = ["cfg-expr/targets"]
 cargo_metadata = "0.15"
 # Used to parse and evaluate cfg() expressions for dependencies
 cfg-expr = "0.11"
+# Allows inspection of the cargo registry index(ices)
+crates-index = { version = "0.18", optional = true, default-features = false, features = [
+    "parallel",
+] }
 # Used to create and traverse graph structures
 petgraph = "0.6"
 # Used for checking version requirements

deny.toml

@@ -9,6 +9,7 @@ allow = [
     "Apache-2.0",
     "Apache-2.0 WITH LLVM-exception",
     "MIT",
+    "MPL-2.0",
     "Unicode-DFS-2016",
 ]
 copyleft = "deny"

src/builder.rs

@@ -767,13 +767,16 @@ impl Builder {
             features: Vec<String>,
         }
 
+        #[cfg(feature = "crates-index")]
+        let index = crates_index::Index::new_cargo_default().ok();
+
         while let Some(pid) = pid_stack.pop() {
             let is_in_workspace = workspace_members.binary_search(pid).is_ok();
 
             let krate_index = nodes.binary_search_by(|n| n.id.cmp(pid)).unwrap();
 
             let rnode = &nodes[krate_index];
-            let krate = &packages[krate_index];
+            let krate = &mut packages[krate_index];
 
             if exclude.iter().any(|exc| exc.matches(krate)) {
                 continue;
@@ -805,6 +808,11 @@ impl Builder {
                 }
             };
 
+            #[cfg(feature = "prefer-index")]
+            if let Some(index) = &index {
+                fix_features(index, krate);
+            }
+
             // Cargo puts out a flat list of the enabled features, but we need
             // to use the declared features on the crate itself to figure out
             // the actual chain of features from one crate to another
@@ -860,9 +868,10 @@ impl Builder {
                 .features
                 .iter()
                 .filter_map(|feat| {
-                    // This should never fail as cargo will not generate metadata if
-                    // a feature is mentioned that doesn't exist, but still no
-                    // reason to panic here
+                    // This _should_ never fail in normal cases, however if the
+                    // `prefer-index` feature is not enabled, it's possible for
+                    // the resolved features to mention features that aren't in
+                    // the actual crate manifest
                     let sub_feats: Vec<_> = krate
                         .features
                         .get(feat)?
@@ -1049,7 +1058,17 @@ impl Builder {
                     let mut features: Vec<String> = Vec::new();
 
                     while let Some(feat) = feature_stack.pop() {
-                        for sf in &krate.features[feat] {
+                        // This _should_ never fail in normal cases, however if the
+                        // `prefer-index` feature is not enabled, it's possible for
+                        // the resolved features to mention features that aren't in
+                        // the actual crate manifest
+                        let fs = if let Some(fs) = krate.features.get(feat) {
+                            fs
+                        } else {
+                            // TODO: Show the user a warning, or just fail?
+                            continue;
+                        };
+                        for sf in fs {
                             let pf = ParsedFeature::from(sf.as_str());
 
                             let (krate, feature) = match pf.feat() {
@@ -1439,6 +1458,66 @@ fn dep_names_match(krate_dep_name: &str, resolved_name: &str) -> bool {
     }
 }
 
+/// Due to <https://github.com/rust-lang/cargo/issues/11319>, we can't actually
+/// trust cargo to give us the correct package metadata, so we instead use the
+/// (presumably) correct data from the the index
+#[cfg(feature = "prefer-index")]
+fn fix_features(index: &crates_index::Index, krate: &mut cm::Package) {
+    if krate
+        .source
+        .as_ref()
+        .map_or(true, |src| !src.is_crates_io())
+    {
+        return;
+    }
+
+    if let Some(entry) = index.crate_(&krate.name) {
+        let features = entry.versions().iter().find_map(|v| {
+            if let Ok(iv) = v.version().parse::<semver::Version>() {
+                if iv == krate.version {
+                    Some(v.features())
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        });
+
+        if let Some(features) = features {
+            krate.features = features.clone();
+
+            // The index entry features might not have the `dep:<crate>`
+            // used with weak features if the crate version was
+            // published with cargo <1.60.0 version, so we need to
+            // manually fix that up since we depend on that format
+            let missing_deps: Vec<_> = krate
+                .features
+                .iter()
+                .flat_map(|(_, sf)| sf.iter())
+                .filter_map(|sf| {
+                    let pf = ParsedFeature::from(sf.as_str());
+
+                    if let Feature::Simple(simple) = pf.feat() {
+                        if krate.features.contains_key(simple) {
+                            None
+                        } else {
+                            Some(simple.to_owned())
+                        }
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+
+            for missing in missing_deps {
+                let dep_feature = format!("dep:{missing}");
+                krate.features.insert(missing, vec![dep_feature]);
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

tests/bug/Cargo.toml

@@ -3,6 +3,9 @@ name = "bug"
 version = "0.1.0"
 edition = "2021"
 
+[dependencies]
+conv = "=0.3.3"
+
 [dependencies.wasmtime]
 version = "2.0.0"
 default-features = false

tests/misc.rs

@@ -191,6 +191,7 @@ fn direct_dependencies() {
 }
 
 #[test]
+#[cfg(feature = "prefer-index")]
 fn bug_repro() {
     let kb = krates::Builder::new();