wit-parser: Use stability info when processing foreign deps

Previously, the process_foreign_interfaces function would
receive unresolved interfaces with their stability values
set to Unknown

This made it hard to distinguish between interfaces which
had been feature gated out, and genuinely nonexistent
interfaces

This commit records the stability of a foreign dependency when
populating the self.foreign_{deps, interfaces, worlds}
maps, which enables process_foreign_interfaces to push a placeholder
for a feature-gated interface, and fail on non-existent interfaces

Fixes issue 2285

Author: danielvallance

crates/wit-parser/src/ast/resolve.rs

@@ -257,7 +257,7 @@ impl<'a> Resolver<'a> {
         let mut foreign_worlds = mem::take(&mut self.foreign_worlds);
         for decl_list in decl_lists {
             decl_list
-                .for_each_path(&mut |_, _attrs, path, _names, world_or_iface| {
+                .for_each_path(&mut |_, attrs, path, _names, world_or_iface| {
                     let (id, name) = match path {
                         ast::UsePath::Package { id, name } => (id, name),
                         _ => return Ok(()),
@@ -290,6 +290,14 @@ impl<'a> Resolver<'a> {
                         }
                     });
 
+                    let stability = self.stability(attrs)?;
+                    if stability != Stability::Unknown {
+                        match id {
+                            AstItem::Interface(id) => self.interfaces[id].stability = stability,
+                            AstItem::World(id) => self.worlds[id].stability = stability,
+                        }
+                    }
+
                     let _ = match id {
                         AstItem::Interface(id) => foreign_interfaces.insert(id),
                         AstItem::World(id) => foreign_worlds.insert(id),

crates/wit-parser/src/resolve.rs

@@ -3157,6 +3157,14 @@ impl Remap {
                 // further interfaces will be non-foreign as well.
                 None => break,
             };
+
+            if let Stability::Unstable { feature, .. } = &unresolved_iface.stability {
+                if !resolve.features.contains(feature) && !resolve.all_features {
+                    self.interfaces.push(None);
+                    continue;
+                }
+            }
+
             let pkgid = resolve
                 .package_names
                 .get(pkg_name)

crates/wit-parser/tests/ui/foreign-interface-dep-gated.wit

@@ -0,0 +1,17 @@
+package a:b1;
+
+world the-world {
+  include a:b2/the-world;
+}
+
+package a:b2 {
+  world the-world {
+    @unstable(feature = disabled)
+    import a:b3/thing;
+  }
+}
+
+package a:b3 {
+  @unstable(feature = disabled)
+  interface thing {}
+}

crates/wit-parser/tests/ui/foreign-interface-dep-gated.wit.json

@@ -0,0 +1,39 @@
+{
+  "worlds": [
+    {
+      "name": "the-world",
+      "imports": {},
+      "exports": {},
+      "package": 1
+    },
+    {
+      "name": "the-world",
+      "imports": {},
+      "exports": {},
+      "package": 2
+    }
+  ],
+  "interfaces": [],
+  "types": [],
+  "packages": [
+    {
+      "name": "a:b3",
+      "interfaces": {},
+      "worlds": {}
+    },
+    {
+      "name": "a:b2",
+      "interfaces": {},
+      "worlds": {
+        "the-world": 0
+      }
+    },
+    {
+      "name": "a:b1",
+      "interfaces": {},
+      "worlds": {
+        "the-world": 1
+      }
+    }
+  ]
+}

crates/wit-parser/tests/ui/foreign-world-dep-gated.wit

@@ -0,0 +1,17 @@
+package a:b1;
+
+world the-world {
+  include a:b2/the-world;
+}
+
+package a:b2 {
+  world the-world {
+    @unstable(feature = disabled)
+    import a:b3/another-world;
+  }
+}
+
+package a:b3 {
+  @unstable(feature = disabled)
+  world another-world {}
+}

crates/wit-parser/tests/ui/foreign-world-dep-gated.wit.json

@@ -0,0 +1,39 @@
+{
+  "worlds": [
+    {
+      "name": "the-world",
+      "imports": {},
+      "exports": {},
+      "package": 1
+    },
+    {
+      "name": "the-world",
+      "imports": {},
+      "exports": {},
+      "package": 2
+    }
+  ],
+  "interfaces": [],
+  "types": [],
+  "packages": [
+    {
+      "name": "a:b3",
+      "interfaces": {},
+      "worlds": {}
+    },
+    {
+      "name": "a:b2",
+      "interfaces": {},
+      "worlds": {
+        "the-world": 0
+      }
+    },
+    {
+      "name": "a:b1",
+      "interfaces": {},
+      "worlds": {
+        "the-world": 1
+      }
+    }
+  ]
+}