Allow macro definitions to pick up precise C types

Upon activating the `--macro-const-use-ctypes` flag, `bindgen` should
generate bindings with precise type resolution to the exact C types.

This flag implies `--clang-macro-fallback` as its pre-requisite.

Signed-off-by: Xiangfei Ding <dingxiangfei2009@protonmail.ch>

Author: dingxiangfei2009

bindgen-tests/tests/expectations/tests/issue-753.rs

@@ -7,6 +7,6 @@
 
 #define CONST UINT32_C(5)
 #define OTHER_CONST UINT32_C(6)
-#define LARGE_CONST UINT32_C(6 << 8)
+#define LARGE_CONST (UINT32_C(6) << 8)
 
 #endif

bindgen-tests/tests/expectations/tests/issue-923.rs

@@ -0,0 +1,4 @@
+// bindgen-flags: --macro-const-use-ctypes
+#define ULONG_ZERO 0UL
+#define ULONGLONG_ZERO 0ULL
+#define CHAR_ZERO ((char)'\0')

bindgen-tests/tests/expectations/tests/test_macro_fallback_non_system_dir.rs

@@ -2329,7 +2329,8 @@ impl EvalResult {
         })
     }
 
-    fn kind(&self) -> CXEvalResultKind {
+    /// Return the kind of the evaluation result.
+    pub(crate) fn kind(&self) -> CXEvalResultKind {
         unsafe { clang_EvalResult_getKind(self.x) }
     }
 
@@ -2370,6 +2371,29 @@ impl EvalResult {
         Some(value as i64)
     }
 
+    /// Try to resolve the result into a string literal.
+    /// This returns `None` if the result is not immediately a string literal.
+    pub(crate) fn as_str_literal(&self) -> Option<Vec<u8>> {
+        if !matches!(
+            self.kind(),
+            CXEval_StrLiteral | CXEval_CFStr | CXEval_ObjCStrLiteral,
+        ) {
+            return None;
+        }
+        // Safety: we are only copying the content, not assuming a borrow.
+        // TODO(@dingxiangfei2009): LLVM Libclang does not return the true size
+        // of a string literal, which could be truncated due to a null character
+        // '\0' in the middle.
+        let value =
+            unsafe { CStr::from_ptr(clang_EvalResult_getAsStr(self.x)) };
+        Some(value.to_bytes().into())
+    }
+
+    /// Return the type of the value.
+    pub(crate) fn value_type(&self) -> Type {
+        self.ty
+    }
+
     /// Evaluates the expression as a literal string, that may or may not be
     /// valid utf-8.
     pub(crate) fn as_literal_string(&self) -> Option<Vec<u8>> {

bindgen-tests/tests/headers/issue-753.h

@@ -353,7 +353,7 @@ pub(crate) struct BindgenContext {
     /// hard errors while parsing duplicated macros, as well to allow macro
     /// expression parsing.
     ///
-    /// This needs to be an `std::HashMap` because the `cexpr` API requires it.
+    /// This needs to be an `std::HashMap` because the [`cexpr`] API requires it.
     parsed_macros: StdHashMap<Vec<u8>, cexpr::expr::EvalResult>,
 
     /// A map with all include locations.
@@ -2129,6 +2129,7 @@ If you encounter an error missing from this list, please file an issue or a PR!"
     }
 
     /// Get the currently parsed macros.
+    /// This map only contains macros accepted by [`cexpr`]
     pub(crate) fn parsed_macros(
         &self,
     ) -> &StdHashMap<Vec<u8>, cexpr::expr::EvalResult> {