Add option to fit macro consts into smaller types

Add a `--fit-macro-constant-types` option to make bindgen try to fit
macro integer constants into types smaller than u32/i32.
Useful especially when dealing with 8/16-bit architectures.

Closes rust-lang#1945

src/ir/var.rs

@@ -117,21 +117,53 @@ impl DotAttributes for Var {
     }
 }
 
-// TODO(emilio): we could make this more (or less) granular, I guess.
 fn default_macro_constant_type(ctx: &BindgenContext, value: i64) -> IntKind {
-    if value < 0 ||
-        ctx.options().default_macro_constant_type ==
-            MacroTypeVariation::Signed
-    {
-        if value < i32::min_value() as i64 || value > i32::max_value() as i64 {
-            IntKind::I64
+    if ctx.options().fit_macro_constants {
+        if value < 0 ||
+            ctx.options().default_macro_constant_type ==
+                MacroTypeVariation::Signed
+        {
+            if value < i32::min_value() as i64 ||
+                value > i32::max_value() as i64
+            {
+                IntKind::I64
+            } else if value < i16::min_value() as i64 ||
+                value > i16::max_value() as i64
+            {
+                IntKind::I32
+            } else if value < i8::min_value() as i64 ||
+                value > i8::max_value() as i64
+            {
+                IntKind::I16
+            } else {
+                IntKind::I8
+            }
+        } else if value > u32::max_value() as i64 {
+            IntKind::U64
+        } else if value > u16::max_value() as i64 {
+            IntKind::U32
+        } else if value > u8::max_value() as i64 {
+            IntKind::U16
         } else {
-            IntKind::I32
+            IntKind::U8
         }
-    } else if value > u32::max_value() as i64 {
-        IntKind::U64
     } else {
-        IntKind::U32
+        if value < 0 ||
+            ctx.options().default_macro_constant_type ==
+                MacroTypeVariation::Signed
+        {
+            if value < i32::min_value() as i64 ||
+                value > i32::max_value() as i64
+            {
+                IntKind::I64
+            } else {
+                IntKind::I32
+            }
+        } else if value > u32::max_value() as i64 {
+            IntKind::U64
+        } else {
+            IntKind::U32
+        }
     }
 }
 

src/lib.rs

@@ -478,6 +478,10 @@ impl Builder {
             output_vector.push("--no-prepend-enum-name".into());
         }
 
+        if self.options.fit_macro_constants {
+            output_vector.push("--fit-macro-constant-types".into());
+        }
+
         if self.options.array_pointers_in_arguments {
             output_vector.push("--use-array-pointers-in-arguments".into());
         }
@@ -1287,6 +1291,12 @@ impl Builder {
         self
     }
 
+    /// Whether to try to fit macro constants to types smaller than u32/i32
+    pub fn fit_macro_constants(mut self, doit: bool) -> Self {
+        self.options.fit_macro_constants = doit;
+        self
+    }
+
     /// Prepend the enum name to constant or newtype variants.
     pub fn prepend_enum_name(mut self, doit: bool) -> Self {
         self.options.prepend_enum_name = doit;
@@ -1735,6 +1745,9 @@ struct BindgenOptions {
     /// Whether to detect include paths using clang_sys.
     detect_include_paths: bool,
 
+    /// Whether to try to fit macro constants into types smaller than u32/i32
+    fit_macro_constants: bool,
+
     /// Whether to prepend the enum name to constant or newtype variants.
     prepend_enum_name: bool,
 
@@ -1905,6 +1918,7 @@ impl Default for BindgenOptions {
             block_extern_crate: false,
             enable_mangling: true,
             detect_include_paths: true,
+            fit_macro_constants: false,
             prepend_enum_name: true,
             time_phases: false,
             record_matches: true,

src/options.rs

@@ -316,6 +316,9 @@ where
             Arg::with_name("no-include-path-detection")
                 .long("no-include-path-detection")
                 .help("Do not try to detect default include paths"),
+            Arg::with_name("fit-macro-constant-types")
+                .long("fit-macro-constant-types")
+                .help("Try to fit macro constants into types smaller than u32/i32"),
             Arg::with_name("unstable-rust")
                 .long("unstable-rust")
                 .help("Generate unstable Rust code (deprecated; use --rust-target instead).")
@@ -654,6 +657,10 @@ where
         builder = builder.detect_include_paths(false);
     }
 
+    if matches.is_present("fit-macro-constant-types") {
+        builder = builder.fit_macro_constants(true);
+    }
+
     if matches.is_present("time-phases") {
         builder = builder.time_phases(true);
     }

tests/expectations/tests/default-macro-constant-type-signed.rs

@@ -10,6 +10,18 @@ pub const N1: i32 = 1;
 pub const N2: i32 = 2;
 pub const N_1: i32 = -1;
 pub const N_2: i32 = -2;
+pub const MAX_U16: i32 = 65535;
+pub const MAX_I16: i32 = 32767;
+pub const MAX_I16_Plus1: i32 = 32768;
+pub const MAX_U16_Plus1: i32 = 65536;
+pub const MAX_I16_Minus1: i32 = 32766;
+pub const MAX_U16_Minus1: i32 = 65534;
+pub const MIN_U16: i32 = 0;
+pub const MIN_I16: i32 = -32768;
+pub const MIN_U16_Plus1: i32 = 1;
+pub const MIN_I16_Plus1: i32 = -32767;
+pub const MIN_U16_Minus1: i32 = -1;
+pub const MIN_I16_Minus1: i32 = -32769;
 pub const MAX_U32: i64 = 4294967295;
 pub const MAX_I32: i32 = 2147483647;
 pub const MAX_I32_Plus1: i64 = 2147483648;

tests/expectations/tests/default-macro-constant-type-unsigned.rs

@@ -10,6 +10,18 @@ pub const N1: u32 = 1;
 pub const N2: u32 = 2;
 pub const N_1: i32 = -1;
 pub const N_2: i32 = -2;
+pub const MAX_U16: u32 = 65535;
+pub const MAX_I16: u32 = 32767;
+pub const MAX_I16_Plus1: u32 = 32768;
+pub const MAX_U16_Plus1: u32 = 65536;
+pub const MAX_I16_Minus1: u32 = 32766;
+pub const MAX_U16_Minus1: u32 = 65534;
+pub const MIN_U16: u32 = 0;
+pub const MIN_I16: i32 = -32768;
+pub const MIN_U16_Plus1: u32 = 1;
+pub const MIN_I16_Plus1: i32 = -32767;
+pub const MIN_U16_Minus1: i32 = -1;
+pub const MIN_I16_Minus1: i32 = -32769;
 pub const MAX_U32: u32 = 4294967295;
 pub const MAX_I32: u32 = 2147483647;
 pub const MAX_I32_Plus1: u32 = 2147483648;

tests/expectations/tests/default-macro-constant-type.rs

@@ -10,6 +10,18 @@ pub const N1: u32 = 1;
 pub const N2: u32 = 2;
 pub const N_1: i32 = -1;
 pub const N_2: i32 = -2;
+pub const MAX_U16: u32 = 65535;
+pub const MAX_I16: u32 = 32767;
+pub const MAX_I16_Plus1: u32 = 32768;
+pub const MAX_U16_Plus1: u32 = 65536;
+pub const MAX_I16_Minus1: u32 = 32766;
+pub const MAX_U16_Minus1: u32 = 65534;
+pub const MIN_U16: u32 = 0;
+pub const MIN_I16: i32 = -32768;
+pub const MIN_U16_Plus1: u32 = 1;
+pub const MIN_I16_Plus1: i32 = -32767;
+pub const MIN_U16_Minus1: i32 = -1;
+pub const MIN_I16_Minus1: i32 = -32769;
 pub const MAX_U32: u32 = 4294967295;
 pub const MAX_I32: u32 = 2147483647;
 pub const MAX_I32_Plus1: u32 = 2147483648;

tests/expectations/tests/fit-macro-constant-types.rs

@@ -0,0 +1,54 @@
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+pub const N0: u8 = 0;
+pub const N1: u8 = 1;
+pub const N2: u8 = 2;
+pub const N_1: i8 = -1;
+pub const N_2: i8 = -2;
+pub const MAX_U16: u16 = 65535;
+pub const MAX_I16: u16 = 32767;
+pub const MAX_I16_Plus1: u16 = 32768;
+pub const MAX_U16_Plus1: u32 = 65536;
+pub const MAX_I16_Minus1: u16 = 32766;
+pub const MAX_U16_Minus1: u16 = 65534;
+pub const MIN_U16: u8 = 0;
+pub const MIN_I16: i16 = -32768;
+pub const MIN_U16_Plus1: u8 = 1;
+pub const MIN_I16_Plus1: i16 = -32767;
+pub const MIN_U16_Minus1: i8 = -1;
+pub const MIN_I16_Minus1: i32 = -32769;
+pub const MAX_U32: u32 = 4294967295;
+pub const MAX_I32: u32 = 2147483647;
+pub const MAX_I32_Plus1: u32 = 2147483648;
+pub const MAX_U32_Plus1: u64 = 4294967296;
+pub const MAX_I32_Minus1: u32 = 2147483646;
+pub const MAX_U32_Minus1: u32 = 4294967294;
+pub const MIN_U32: u8 = 0;
+pub const MIN_I32: i32 = -2147483648;
+pub const MIN_U32_Plus1: u8 = 1;
+pub const MIN_I32_Plus1: i32 = -2147483647;
+pub const MIN_U32_Minus1: i8 = -1;
+pub const MIN_I32_Minus1: i64 = -2147483649;
+pub const LONG12: u64 = 123456789012;
+pub const LONG_12: i64 = -123456789012;
+extern "C" {
+    pub fn foo(
+        arg1: ::std::os::raw::c_int,
+        arg2: ::std::os::raw::c_int,
+        arg3: ::std::os::raw::c_uint,
+        arg4: ::std::os::raw::c_char,
+        arg5: ::std::os::raw::c_uchar,
+        arg6: ::std::os::raw::c_schar,
+    ) -> ::std::os::raw::c_int;
+}
+extern "C" {
+    pub fn bar(
+        arg1: ::std::os::raw::c_long,
+        arg2: ::std::os::raw::c_longlong,
+    ) -> ::std::os::raw::c_long;
+}

tests/headers/default-macro-constant-type.h

@@ -8,6 +8,24 @@
 #define N_1 (-1LL)
 #define N_2 (-2LL)
 
+#define MAX_U16  0xFFFFULL
+#define MAX_I16 (0x8000ULL - 1)
+
+#define MAX_I16_Plus1 (MAX_I16 + 1)
+#define MAX_U16_Plus1 (MAX_U16 + 1)
+
+#define MAX_I16_Minus1 (MAX_I16 - 1)
+#define MAX_U16_Minus1 (MAX_U16 - 1)
+
+#define MIN_U16 0
+#define MIN_I16 (- (1ULL<<15))
+
+#define MIN_U16_Plus1 (MIN_U16 + 1)
+#define MIN_I16_Plus1 (MIN_I16 + 1)
+
+#define MIN_U16_Minus1 (MIN_U16 - 1)
+#define MIN_I16_Minus1 (MIN_I16 - 1)
+
 #define MAX_U32  0xFFFFFFFFULL
 #define MAX_I32 (0x80000000ULL - 1)
 

tests/headers/fit-macro-constant-types.h

@@ -0,0 +1,4 @@
+// bindgen-flags: --fit-macro-constant-types
+// Test fitting macro constants into smaller integer types
+// Negative values are i8, i16, i32 or i64; others are u8, u16, u32 or u64.
+#include "default-macro-constant-type.h"