Do not emit enum TagName tag when a sized representation is present.

sw17ch · sw17ch · commit df0167becc01 · 2020-01-25T00:26:40.000-08:00
This affected cases where the style was set to `Stle::Tag`.

In enumerations, do not emut the tag type name with an `enum`
prefix. C treats the `enum` type as an `int` even if the
representation should be something else.

Here's an example non-C-like-enumeration:

    #[repr(C, u8)]
    enum P {
        P1(u8),
        P2(u8, u8),
        P3(u8, u8, u8),
    }

Without this patch, this is what's generated:

    enum P_Tag {
      P1,
      P2,
      P3,
    };
    typedef uint8_t P_Tag;

    typedef struct {
      uint8_t _0;
    } P1_Body;

    typedef struct {
      uint8_t _0;
      uint8_t _1;
    } P2_Body;

    typedef struct {
      uint8_t _0;
      uint8_t _1;
      uint8_t _2;
    } P3_Body;

    typedef struct {
      enum P_Tag tag;
      union {
        P1_Body p1;
        P2_Body p2;
        P3_Body p3;
      };
    } P;

Rust expects the size of the type to be 4 (one for the discriminant,
and 3 for the widest alternative. C, however, treats the `enum P_Tag
tag` field as an `int` rather than a `uint8_t`. This puts the size
(with padding) of of `P` to 8 bytes instead of 4. When passing this
type between Rust and C, they will disagree on the size.

After the patch is applied, the `P` struct is properly defined:

    typedef struct {
      P_Tag tag;
      union {
        P1_Body p1;
        P2_Body p2;
        P3_Body p3;
      };
    } P;
diff --git a/src/bindgen/ir/enumeration.rs b/src/bindgen/ir/enumeration.rs
@@ -682,7 +682,8 @@ impl Source for Enum {
                 out.open_brace();
             }
 
-            if config.language == Language::C && !config.style.generate_typedef() {
+            if config.language == Language::C && !size.is_some() && !config.style.generate_typedef()
+            {
                 out.write("enum ");
             }
 

Original file line number	Diff line number	Diff line change
`@@ -682,7 +682,8 @@ impl Source for Enum {`
`682`	`682`	`out.open_brace();`
`683`	`683`	`}`
`684`	`684`
`685`		`- if config.language == Language::C && !config.style.generate_typedef() {`
	`685`	`+ if config.language == Language::C && !size.is_some() && !config.style.generate_typedef()`
	`686`	`+ {`
`686`	`687`	`out.write("enum ");`
`687`	`688`	`}`
`688`	`689`