Add support for non_exhaustive rustified enums.

Implements the feature discussed in
rust-lang#1554.

Author: agodnic

src/codegen/helpers.rs

@@ -42,6 +42,12 @@ pub mod attributes {
         }
     }
 
+    pub fn non_exhaustive() -> TokenStream {
+        quote! {
+            #[non_exhaustive]
+        }
+    }
+
     pub fn doc(comment: String) -> TokenStream {
         // NOTE(emilio): By this point comments are already preprocessed and in
         // `///` form. Quote turns them into `#[doc]` comments, but oh well.

src/codegen/mod.rs

@@ -2170,7 +2170,10 @@ impl MethodCodegen for Method {
 #[derive(Copy, Clone, PartialEq, Debug)]
 pub enum EnumVariation {
     /// The code for this enum will use a Rust enum
-    Rust,
+    ///
+    /// When the boolean parameter on this variant is set to true,
+    /// the generated enum should be non_exhaustive.
+    Rust(bool),
     /// The code for this enum will use a bitfield
     Bitfield,
     /// The code for this enum will use consts
@@ -2182,14 +2185,7 @@ pub enum EnumVariation {
 impl EnumVariation {
     fn is_rust(&self) -> bool {
         match *self {
-            EnumVariation::Rust => true,
-            _ => false
-        }
-    }
-
-    fn is_bitfield(&self) -> bool {
-        match *self {
-            EnumVariation::Bitfield {..} => true,
+            EnumVariation::Rust(_) => true,
             _ => false
         }
     }
@@ -2216,13 +2212,14 @@ impl std::str::FromStr for EnumVariation {
     /// Create a `EnumVariation` from a string.
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         match s {
-            "rust" => Ok(EnumVariation::Rust),
+            "rust" => Ok(EnumVariation::Rust(false)),
+            "rust_non_exhaustive" => Ok(EnumVariation::Rust(true)),
             "bitfield" => Ok(EnumVariation::Bitfield),
             "consts" => Ok(EnumVariation::Consts),
             "moduleconsts" => Ok(EnumVariation::ModuleConsts),
             _ => Err(std::io::Error::new(std::io::ErrorKind::InvalidInput,
                                          concat!("Got an invalid EnumVariation. Accepted values ",
-                                                 "are 'rust', 'bitfield', 'consts', and ",
+                                                 "are 'rust', 'rust_non_exhaustive', 'bitfield', 'consts', and ",
                                                  "'moduleconsts'."))),
         }
     }
@@ -2288,7 +2285,7 @@ impl<'a> EnumBuilder<'a> {
                 }
             }
 
-            EnumVariation::Rust => {
+            EnumVariation::Rust(_) => {
                 let tokens = quote!();
                 EnumBuilder::Rust {
                     codegen_depth: enum_codegen_depth + 1,
@@ -2580,15 +2577,22 @@ impl CodeGenerator for Enum {
         let variation = self.computed_enum_variation(ctx, item);
 
         // TODO(emilio): Delegate this to the builders?
-        if variation.is_rust() {
-            attrs.push(attributes::repr(repr_name));
-        } else if variation.is_bitfield() {
-            if ctx.options().rust_features.repr_transparent {
-                attrs.push(attributes::repr("transparent"));
-            } else {
-                attrs.push(attributes::repr("C"));
-            }
-        }
+        match variation {
+            EnumVariation::Rust(non_exhaustive) => {
+                attrs.push(attributes::repr(repr_name));
+                if non_exhaustive {
+                    attrs.push(attributes::non_exhaustive());
+                }
+            },
+            EnumVariation::Bitfield => {
+                if ctx.options().rust_features.repr_transparent {
+                    attrs.push(attributes::repr("transparent"));
+                } else {
+                    attrs.push(attributes::repr("C"));
+                }
+            },
+            _ => {},
+        };
 
         if let Some(comment) = item.comment(ctx) {
             attrs.push(attributes::doc(comment));

src/ir/enum_ty.rs

@@ -164,7 +164,9 @@ impl Enum {
         } else if self.is_matching_enum(ctx, &ctx.options().bitfield_enums, item) {
             EnumVariation::Bitfield
         } else if self.is_matching_enum(ctx, &ctx.options().rustified_enums, item) {
-            EnumVariation::Rust
+            EnumVariation::Rust(false)
+        } else if self.is_matching_enum(ctx, &ctx.options().rustified_enums_non_exhaustive, item) {
+            EnumVariation::Rust(true)
         } else if self.is_matching_enum(ctx, &ctx.options().constified_enums, item) {
             EnumVariation::Consts
         } else {

src/lib.rs

@@ -226,7 +226,8 @@ impl Builder {
         if self.options.default_enum_style != Default::default() {
             output_vector.push("--default-enum-style=".into());
             output_vector.push(match self.options.default_enum_style {
-                codegen::EnumVariation::Rust => "rust",
+                codegen::EnumVariation::Rust(false) => "rust",
+                codegen::EnumVariation::Rust(true) => "rust_non_exhaustive",
                 codegen::EnumVariation::Bitfield => "bitfield",
                 codegen::EnumVariation::Consts => "consts",
                 codegen::EnumVariation::ModuleConsts => "moduleconsts",
@@ -253,6 +254,16 @@ impl Builder {
             })
             .count();
 
+        self.options
+            .rustified_enums_non_exhaustive
+            .get_items()
+            .iter()
+            .map(|item| {
+                output_vector.push("--rustified-enum-non-exhaustive".into());
+                output_vector.push(item.to_owned());
+            })
+            .count();
+
         self.options
             .constified_enum_modules
             .get_items()
@@ -810,15 +821,24 @@ impl Builder {
     /// This makes bindgen generate enums instead of constants. Regular
     /// expressions are supported.
     ///
-    /// **Use this with caution.** You should not be using Rust enums unless
-    /// you have complete control of the C/C++ code that you're binding to.
-    /// Take a look at https://github.com/rust-lang/rust/issues/36927 for
-    /// more information.
+    /// **Use this with caution,** you probably want to use the non_exhaustive
+    /// flavor of rust enums instead of this one. Take a look at
+    /// https://github.com/rust-lang/rust/issues/36927 for more information.
     pub fn rustified_enum<T: AsRef<str>>(mut self, arg: T) -> Builder {
         self.options.rustified_enums.insert(arg);
         self
     }
 
+    /// Mark the given enum (or set of enums, if using a pattern) as a Rust
+    /// enum with the #[non_exhaustive] attribute.
+    ///
+    /// This makes bindgen generate enums instead of constants. Regular
+    /// expressions are supported.
+    pub fn rustified_enum_non_exhaustive<T: AsRef<str>>(mut self, arg: T) -> Builder {
+        self.options.rustified_enums_non_exhaustive.insert(arg);
+        self
+    }
+
     /// Mark the given enum (or set of enums, if using a pattern) as a set of
     /// constants that are not to be put into a module.
     pub fn constified_enum<T: AsRef<str>>(mut self, arg: T) -> Builder {
@@ -1367,6 +1387,8 @@ struct BindgenOptions {
     /// The enum patterns to mark an enum as a Rust enum.
     rustified_enums: RegexSet,
 
+    rustified_enums_non_exhaustive: RegexSet,
+
     /// The enum patterns to mark an enum as a module of constants.
     constified_enum_modules: RegexSet,
 
@@ -1620,6 +1642,7 @@ impl Default for BindgenOptions {
             default_enum_style: Default::default(),
             bitfield_enums: Default::default(),
             rustified_enums: Default::default(),
+            rustified_enums_non_exhaustive: Default::default(),
             constified_enums: Default::default(),
             constified_enum_modules: Default::default(),
             builtins: false,

src/options.rs

@@ -31,7 +31,7 @@ where
                 .help("The default style of code used to generate enums.")
                 .value_name("variant")
                 .default_value("consts")
-                .possible_values(&["consts", "moduleconsts", "bitfield", "rust"])
+                .possible_values(&["consts", "moduleconsts", "bitfield", "rust", "rust_non_exhaustive"])
                 .multiple(false),
             Arg::with_name("bitfield-enum")
                 .long("bitfield-enum")

tests/expectations/tests/issue-1554.rs

@@ -0,0 +1,16 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+#[repr(u32)]
+#[non_exhaustive]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum Planet {
+    earth = 0,
+    mars = 1,
+}

tests/headers/issue-1554.h

@@ -0,0 +1,6 @@
+// bindgen-flags: --default-enum-style rust_non_exhaustive
+
+enum Planet {
+    earth,
+    mars
+};