Follow-up to mozilla#582 to address review comment.

This avoids propagating the derive-ostream annotation from an enum to
the variant body if the variant body already has an explicit annotation
set. This allows for more possibilities ending in compilation failure
but generally only when the user explicitly sets these annotations without
defining necessary serializers themselves. We should be able to assume
the user knows what they're doing if they trigger these particular scenarios.

src/bindgen/ir/annotation.rs

@@ -119,6 +119,10 @@ impl AnnotationSet {
         self.annotations.insert(name.to_string(), value);
     }
 
+    pub fn contains(&self, name: &str) -> bool {
+        self.annotations.contains_key(name)
+    }
+
     pub fn list(&self, name: &str) -> Option<Vec<String>> {
         match self.annotations.get(name) {
             Some(&AnnotationValue::List(ref x)) => Some(x.clone()),

src/bindgen/ir/enumeration.rs

@@ -144,8 +144,10 @@ impl EnumVariant {
 
         let variant_cfg = Cfg::append(mod_cfg, Cfg::load(&variant.attrs));
         let mut annotations = AnnotationSet::load(&variant.attrs)?;
-        if let Some(b) = enum_annotations.bool("derive-ostream") {
-            annotations.add("derive-ostream", AnnotationValue::Bool(b));
+        if !annotations.contains("derive-ostream") {
+            if let Some(b) = enum_annotations.bool("derive-ostream") {
+                annotations.add("derive-ostream", AnnotationValue::Bool(b));
+            }
         }
         let body = match variant.fields {
             syn::Fields::Unit => VariantBody::Empty(annotations),

tests/expectations/both/derive_ostream.c

@@ -72,4 +72,27 @@ typedef struct H {
   };
 } H;
 
-void root(A a, B b, C c, D d, F f, H h);
+enum J_Tag {
+  Hi,
+  Peoples,
+};
+typedef uint8_t J_Tag;
+
+typedef struct Hi_Body {
+  int16_t _0;
+} Hi_Body;
+
+typedef struct Peoples_Body {
+  uint8_t x;
+  int16_t y;
+} Peoples_Body;
+
+typedef struct J {
+  J_Tag tag;
+  union {
+    Hi_Body hi;
+    Peoples_Body peoples;
+  };
+} J;
+
+void root(A a, B b, C c, D d, F f, H h, J j);

tests/expectations/both/derive_ostream.compat.c

@@ -90,11 +90,40 @@ typedef struct H {
   };
 } H;
 
+enum J_Tag
+#ifdef __cplusplus
+  : uint8_t
+#endif // __cplusplus
+ {
+  Hi,
+  Peoples,
+};
+#ifndef __cplusplus
+typedef uint8_t J_Tag;
+#endif // __cplusplus
+
+typedef struct Hi_Body {
+  int16_t _0;
+} Hi_Body;
+
+typedef struct Peoples_Body {
+  uint8_t x;
+  int16_t y;
+} Peoples_Body;
+
+typedef struct J {
+  J_Tag tag;
+  union {
+    Hi_Body hi;
+    Peoples_Body peoples;
+  };
+} J;
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
 
-void root(A a, B b, C c, D d, F f, H h);
+void root(A a, B b, C c, D d, F f, H h, J j);
 
 #ifdef __cplusplus
 } // extern "C"

tests/expectations/derive_ostream.c

@@ -72,4 +72,27 @@ typedef struct {
   };
 } H;
 
-void root(A a, B b, C c, D d, F f, H h);
+enum J_Tag {
+  Hi,
+  Peoples,
+};
+typedef uint8_t J_Tag;
+
+typedef struct {
+  int16_t _0;
+} Hi_Body;
+
+typedef struct {
+  uint8_t x;
+  int16_t y;
+} Peoples_Body;
+
+typedef struct {
+  J_Tag tag;
+  union {
+    Hi_Body hi;
+    Peoples_Body peoples;
+  };
+} J;
+
+void root(A a, B b, C c, D d, F f, H h, J j);

tests/expectations/derive_ostream.compat.c

@@ -90,11 +90,40 @@ typedef struct {
   };
 } H;
 
+enum J_Tag
+#ifdef __cplusplus
+  : uint8_t
+#endif // __cplusplus
+ {
+  Hi,
+  Peoples,
+};
+#ifndef __cplusplus
+typedef uint8_t J_Tag;
+#endif // __cplusplus
+
+typedef struct {
+  int16_t _0;
+} Hi_Body;
+
+typedef struct {
+  uint8_t x;
+  int16_t y;
+} Peoples_Body;
+
+typedef struct {
+  J_Tag tag;
+  union {
+    Hi_Body hi;
+    Peoples_Body peoples;
+  };
+} J;
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
 
-void root(A a, B b, C c, D d, F f, H h);
+void root(A a, B b, C c, D d, F f, H h, J j);
 
 #ifdef __cplusplus
 } // extern "C"

tests/expectations/derive_ostream.cpp

@@ -151,8 +151,35 @@ struct H {
   };
 };
 
+struct J {
+  enum class Tag : uint8_t {
+    Hi,
+    Peoples,
+  };
+
+  struct Hi_Body {
+    int16_t _0;
+  };
+
+  struct Peoples_Body {
+    uint8_t x;
+    int16_t y;
+
+    friend std::ostream& operator<<(std::ostream& stream, const Peoples_Body& instance) {
+      return stream << "{ " << "x=" << instance.x << ", "
+                            << "y=" << instance.y << " }";
+    }
+  };
+
+  Tag tag;
+  union {
+    Hi_Body hi;
+    Peoples_Body peoples;
+  };
+};
+
 extern "C" {
 
-void root(A a, B b, C c, D d, F f, H h);
+void root(A a, B b, C c, D d, F f, H h, J j);
 
 } // extern "C"

tests/expectations/tag/derive_ostream.c

@@ -72,4 +72,27 @@ struct H {
   };
 };
 
-void root(struct A a, struct B b, C c, struct D d, union F f, struct H h);
+enum J_Tag {
+  Hi,
+  Peoples,
+};
+typedef uint8_t J_Tag;
+
+struct Hi_Body {
+  int16_t _0;
+};
+
+struct Peoples_Body {
+  uint8_t x;
+  int16_t y;
+};
+
+struct J {
+  J_Tag tag;
+  union {
+    struct Hi_Body hi;
+    struct Peoples_Body peoples;
+  };
+};
+
+void root(struct A a, struct B b, C c, struct D d, union F f, struct H h, struct J j);

tests/expectations/tag/derive_ostream.compat.c

@@ -90,11 +90,40 @@ struct H {
   };
 };
 
+enum J_Tag
+#ifdef __cplusplus
+  : uint8_t
+#endif // __cplusplus
+ {
+  Hi,
+  Peoples,
+};
+#ifndef __cplusplus
+typedef uint8_t J_Tag;
+#endif // __cplusplus
+
+struct Hi_Body {
+  int16_t _0;
+};
+
+struct Peoples_Body {
+  uint8_t x;
+  int16_t y;
+};
+
+struct J {
+  J_Tag tag;
+  union {
+    struct Hi_Body hi;
+    struct Peoples_Body peoples;
+  };
+};
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
 
-void root(struct A a, struct B b, C c, struct D d, union F f, struct H h);
+void root(struct A a, struct B b, C c, struct D d, union F f, struct H h, struct J j);
 
 #ifdef __cplusplus
 } // extern "C"

tests/rust/derive_ostream.rs

@@ -38,6 +38,14 @@ enum H {
     Everyone
 }
 
+/// cbindgen:derive-ostream=false
+#[repr(C, u8)]
+enum J {
+    Hi(i16),
+    /// cbindgen:derive-ostream=true
+    Peoples { x: u8, y: i16 },
+}
+
 #[no_mangle]
 pub extern "C" fn root(
     a: A,
@@ -46,5 +54,6 @@ pub extern "C" fn root(
     d: D,
     f: F,
     h: H,
+    j: J,
 ) { }