Fix PhantomData filtering

src/build.rs

@@ -264,39 +264,41 @@ impl<T> FieldsBuilder<T> {
     pub fn finalize(self) -> Vec<Field<MetaForm>> {
         self.fields
     }
+
+    fn push_field(mut self, field: Field) -> Self {
+        // filter out fields of PhantomData
+        if !field.ty().is_phantom() {
+            self.fields.push(field);
+        }
+        self
+    }
 }
 
 impl FieldsBuilder<NamedFields> {
     /// Add a named field constructed using the builder.
-    pub fn field<F>(mut self, builder: F) -> Self
+    pub fn field<F>(self, builder: F) -> Self
     where
         F: Fn(
             FieldBuilder,
         )
             -> FieldBuilder<field_state::NameAssigned, field_state::TypeAssigned>,
     {
         let builder = builder(FieldBuilder::new());
-        let field = builder.finalize();
-        // filter out fields of PhantomData
-        if !field.ty().is_phantom() {
-            self.fields.push(field);
-        }
-        self
+        self.push_field(builder.finalize())
     }
 }
 
 impl FieldsBuilder<UnnamedFields> {
     /// Add an unnamed field constructed using the builder.
-    pub fn field<F>(mut self, builder: F) -> Self
+    pub fn field<F>(self, builder: F) -> Self
     where
         F: Fn(
             FieldBuilder,
         )
             -> FieldBuilder<field_state::NameNotAssigned, field_state::TypeAssigned>,
     {
         let builder = builder(FieldBuilder::new());
-        self.fields.push(builder.finalize());
-        self
+        self.push_field(builder.finalize())
     }
 }
 

src/impls.rs

@@ -329,7 +329,11 @@ impl<T> TypeInfo for PhantomData<T> {
     type Identity = PhantomIdentity;
 
     fn type_info() -> Type {
-        panic!("PhantomData type instances should be filtered out.")
+        // Fields of this type should be filtered out and never appear in the type graph.
+        Type::builder()
+            .path(Path::prelude("PhantomData"))
+            .docs(&["PhantomData placeholder, this type should be filtered out"])
+            .composite(Fields::unit())
     }
 }
 

src/tests.rs

@@ -106,9 +106,14 @@ fn prelude_items() {
 }
 
 #[test]
-#[should_panic]
 fn phantom_data() {
-    PhantomData::<i32>::type_info();
+    assert_type!(
+        PhantomData<i32>,
+        Type::builder()
+            .path(Path::prelude("PhantomData"))
+            .docs(&["PhantomData placeholder, this type should be filtered out"])
+            .composite(Fields::unit())
+    )
 }
 
 #[test]

test_suite/tests/derive.rs

@@ -108,15 +108,21 @@ fn phantom_data_field_is_erased() {
     let ty = Type::builder()
         .path(Path::new("P", "derive"))
         .type_params(named_type_params!((T, bool)))
-        .composite(
-            Fields::named()
-                .field(|f| f.ty::<u8>().name("a").type_name("u8"))
-                .field(|f| {
-                    f.ty::<PhantomData<bool>>()
-                        .name("m")
-                        .type_name("PhantomData<T>")
-                }),
-        );
+        .composite(Fields::named().field(|f| f.ty::<u8>().name("a").type_name("u8")));
+
+    assert_type!(P<bool>, ty);
+}
+
+#[test]
+fn phantom_data_tuple_struct_field_is_erased() {
+    #[allow(unused)]
+    #[derive(TypeInfo)]
+    struct P<T>(u8, PhantomData<T>);
+
+    let ty = Type::builder()
+        .path(Path::new("P", "derive"))
+        .type_params(named_type_params!((T, bool)))
+        .composite(Fields::unnamed().field(|f| f.ty::<u8>().type_name("u8")));
 
     assert_type!(P<bool>, ty);
 }