Generate flexible array members the c99 way instead of the GNU way

There a re three ways to express flexible array members:

1. char fam[0];
2. char fam[1];
3. char fam[];

3. is the only standard way (in c99, but supported in c++ as an
extension), the other two are GNU syntax (still supported in clang
though).

Let's generate the standard syntax by default, while leaving it possible to
use 1. through struct.gnu_flexible_array_members

Cython only supports the 1. mode.

Author: serge-sans-paille

src/bindgen/cdecl.rs

@@ -273,7 +273,7 @@ impl CDecl {
         }
 
         // Write the right part of declarators after the identifier
-        let mut iter = self.declarators.iter();
+        let mut iter = self.declarators.iter().peekable();
         let mut last_was_pointer = false;
 
         #[allow(clippy::while_let_on_iterator)]
@@ -286,7 +286,16 @@ impl CDecl {
                     if last_was_pointer {
                         out.write(")");
                     }
-                    write!(out, "[{}]", constant);
+
+                    let is_fam = constant == "0" && iter.peek().is_none();
+                    if is_fam
+                        && !config.structure.gnu_flexible_array_members
+                        && config.language != Language::Cython
+                    {
+                        write!(out, "[]");
+                    } else {
+                        write!(out, "[{}]", constant);
+                    }
 
                     last_was_pointer = false;
                 }

src/bindgen/config.rs

@@ -499,6 +499,8 @@ pub struct StructConfig {
     pub deprecated: Option<String>,
     /// The way to annotation this function as #[deprecated] with notes
     pub deprecated_with_note: Option<String>,
+    /// The way we represent flexible array members, either GNU style or c99 style
+    pub gnu_flexible_array_members: bool,
 }
 
 impl StructConfig {

tests/expectations/struct.c

@@ -25,4 +25,14 @@ typedef struct {
   float y;
 } TupleNamed;
 
-void root(Opaque *a, Normal b, NormalWithZST c, TupleRenamed d, TupleNamed e);
+typedef struct {
+  int32_t x;
+  int8_t y[];
+} WithFlexibleArrayMember;
+
+void root(Opaque *a,
+          Normal b,
+          NormalWithZST c,
+          TupleRenamed d,
+          TupleNamed e,
+          WithFlexibleArrayMember f);

tests/expectations/struct.compat.c

@@ -25,11 +25,21 @@ typedef struct {
   float y;
 } TupleNamed;
 
+typedef struct {
+  int32_t x;
+  int8_t y[];
+} WithFlexibleArrayMember;
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
 
-void root(Opaque *a, Normal b, NormalWithZST c, TupleRenamed d, TupleNamed e);
+void root(Opaque *a,
+          Normal b,
+          NormalWithZST c,
+          TupleRenamed d,
+          TupleNamed e,
+          WithFlexibleArrayMember f);
 
 #ifdef __cplusplus
 }  // extern "C"

tests/expectations/struct.cpp

@@ -26,8 +26,18 @@ struct TupleNamed {
   float y;
 };
 
+struct WithFlexibleArrayMember {
+  int32_t x;
+  int8_t y[];
+};
+
 extern "C" {
 
-void root(Opaque *a, Normal b, NormalWithZST c, TupleRenamed d, TupleNamed e);
+void root(Opaque *a,
+          Normal b,
+          NormalWithZST c,
+          TupleRenamed d,
+          TupleNamed e,
+          WithFlexibleArrayMember f);
 
 }  // extern "C"

tests/expectations/struct.pyx

@@ -25,4 +25,13 @@ cdef extern from *:
     int32_t x;
     float y;
 
-  void root(Opaque *a, Normal b, NormalWithZST c, TupleRenamed d, TupleNamed e);
+  ctypedef struct WithFlexibleArrayMember:
+    int32_t x;
+    int8_t y[0];
+
+  void root(Opaque *a,
+            Normal b,
+            NormalWithZST c,
+            TupleRenamed d,
+            TupleNamed e,
+            WithFlexibleArrayMember f);

tests/expectations/struct_both.c

@@ -25,8 +25,14 @@ typedef struct TupleNamed {
   float y;
 } TupleNamed;
 
+typedef struct WithFlexibleArrayMember {
+  int32_t x;
+  int8_t y[];
+} WithFlexibleArrayMember;
+
 void root(struct Opaque *a,
           struct Normal b,
           struct NormalWithZST c,
           struct TupleRenamed d,
-          struct TupleNamed e);
+          struct TupleNamed e,
+          struct WithFlexibleArrayMember f);

tests/expectations/struct_both.compat.c

@@ -25,6 +25,11 @@ typedef struct TupleNamed {
   float y;
 } TupleNamed;
 
+typedef struct WithFlexibleArrayMember {
+  int32_t x;
+  int8_t y[];
+} WithFlexibleArrayMember;
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
@@ -33,7 +38,8 @@ void root(struct Opaque *a,
           struct Normal b,
           struct NormalWithZST c,
           struct TupleRenamed d,
-          struct TupleNamed e);
+          struct TupleNamed e,
+          struct WithFlexibleArrayMember f);
 
 #ifdef __cplusplus
 }  // extern "C"

tests/expectations/struct_tag.c

@@ -25,8 +25,14 @@ struct TupleNamed {
   float y;
 };
 
+struct WithFlexibleArrayMember {
+  int32_t x;
+  int8_t y[];
+};
+
 void root(struct Opaque *a,
           struct Normal b,
           struct NormalWithZST c,
           struct TupleRenamed d,
-          struct TupleNamed e);
+          struct TupleNamed e,
+          struct WithFlexibleArrayMember f);

tests/expectations/struct_tag.compat.c

@@ -25,6 +25,11 @@ struct TupleNamed {
   float y;
 };
 
+struct WithFlexibleArrayMember {
+  int32_t x;
+  int8_t y[];
+};
+
 #ifdef __cplusplus
 extern "C" {
 #endif // __cplusplus
@@ -33,7 +38,8 @@ void root(struct Opaque *a,
           struct Normal b,
           struct NormalWithZST c,
           struct TupleRenamed d,
-          struct TupleNamed e);
+          struct TupleNamed e,
+          struct WithFlexibleArrayMember f);
 
 #ifdef __cplusplus
 }  // extern "C"

tests/expectations/struct_tag.pyx

@@ -25,4 +25,13 @@ cdef extern from *:
     int32_t x;
     float y;
 
-  void root(Opaque *a, Normal b, NormalWithZST c, TupleRenamed d, TupleNamed e);
+  cdef struct WithFlexibleArrayMember:
+    int32_t x;
+    int8_t y[0];
+
+  void root(Opaque *a,
+            Normal b,
+            NormalWithZST c,
+            TupleRenamed d,
+            TupleNamed e,
+            WithFlexibleArrayMember f);

tests/rust/struct.rs

@@ -28,11 +28,18 @@ struct TupleRenamed(i32, f32);
 #[repr(C)]
 struct TupleNamed(i32, f32);
 
+#[repr(C)]
+struct WithFlexibleArrayMember {
+    x: i32,
+    y: [i8; 0],
+}
+
 #[no_mangle]
 pub extern "C" fn root(
     a: *mut Opaque,
     b: Normal,
     c: NormalWithZST,
     d: TupleRenamed,
-    e: TupleNamed
+    e: TupleNamed,
+    f: WithFlexibleArrayMember,
 ) { }