Workaround for expansion of funcion-like macros

This commit resolves an issue where macros that evaluate to a constant
but have a function like macro in the macro body would not be properly
expanded by cexpr.

This adds an opt-in option to use Clang on intermediary files to
evaluate the macros one by one. This is opt-in largely because of the
compile time implications.

bindgen-cli/options.rs

@@ -400,6 +400,9 @@ struct BindgenCommand {
     /// Wrap unsafe operations in unsafe blocks.
     #[arg(long)]
     wrap_unsafe_ops: bool,
+    /// Enable fallback for clang macro parsing.
+    #[arg(long)]
+    clang_macro_fallback: bool,
     /// Derive custom traits on any kind of type. The CUSTOM value must be of the shape REGEX=DERIVE where DERIVE is a coma-separated list of derive macros.
     #[arg(long, value_name = "CUSTOM", value_parser = parse_custom_derive)]
     with_derive_custom: Vec<(Vec<String>, String)>,
@@ -554,6 +557,7 @@ where
         merge_extern_blocks,
         override_abi,
         wrap_unsafe_ops,
+        clang_macro_fallback,
         with_derive_custom,
         with_derive_custom_struct,
         with_derive_custom_enum,
@@ -1023,6 +1027,10 @@ where
         builder = builder.wrap_unsafe_ops(true);
     }
 
+    if clang_macro_fallback {
+        builder = builder.clang_macro_fallback();
+    }
+
     #[derive(Debug)]
     struct CustomDeriveCallback {
         derives: Vec<String>,

bindgen/clang.rs

@@ -1868,6 +1868,23 @@ impl TranslationUnit {
         }
     }
 
+    /// Save a translation unit to the given file.
+    pub(crate) fn save(&mut self, file: &str) -> bool {
+        let file = if let Ok(cstring) = CString::new(file) {
+            cstring
+        } else {
+            return false;
+        };
+        let ret = unsafe {
+            clang_saveTranslationUnit(
+                self.x,
+                file.as_ptr(),
+                clang_defaultSaveOptions(self.x),
+            )
+        };
+        ret == 0
+    }
+
     /// Is this the null translation unit?
     pub(crate) fn is_null(&self) -> bool {
         self.x.is_null()
@@ -1882,6 +1899,64 @@ impl Drop for TranslationUnit {
     }
 }
 
+/// Translation unit used for macro fallback parsing
+pub(crate) struct FallbackTranslationUnit {
+    file_path: String,
+    idx: Box<Index>,
+    tu: TranslationUnit,
+}
+
+impl fmt::Debug for FallbackTranslationUnit {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "FallbackTranslationUnit {{ }}")
+    }
+}
+
+impl FallbackTranslationUnit {
+    /// Create a new fallback translation unit
+    pub(crate) fn new(file: &str, c_args: &[Box<str>]) -> Option<Self> {
+        let f_index = Box::new(Index::new(true, false));
+        let f_translation_unit = TranslationUnit::parse(
+            &f_index,
+            file,
+            c_args,
+            &[],
+            CXTranslationUnit_None,
+        )?;
+        Some(FallbackTranslationUnit {
+            file_path: file.to_owned(),
+            tu: f_translation_unit,
+            idx: f_index,
+        })
+    }
+
+    /// Get reference to underlying translation unit.
+    pub(crate) fn translation_unit(&self) -> &TranslationUnit {
+        &self.tu
+    }
+
+    /// Reparse a translation unit.
+    pub(crate) fn reparse(&mut self, unsaved: &[UnsavedFile]) -> bool {
+        let mut c_unsaved: Vec<CXUnsavedFile> =
+            unsaved.iter().map(|f| f.x).collect();
+        let ret = unsafe {
+            clang_reparseTranslationUnit(
+                self.tu.x,
+                unsaved.len() as c_uint,
+                c_unsaved.as_mut_ptr(),
+                CXSaveTranslationUnit_None,
+            )
+        };
+        ret == 0
+    }
+}
+
+impl Drop for FallbackTranslationUnit {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_file(&self.file_path);
+    }
+}
+
 /// A diagnostic message generated while parsing a translation unit.
 pub(crate) struct Diagnostic {
     x: CXDiagnostic,

bindgen/ir/context.rs

@@ -376,6 +376,9 @@ pub(crate) struct BindgenContext {
     /// The translation unit for parsing.
     translation_unit: clang::TranslationUnit,
 
+    /// The translation unit for macro fallback parsing.
+    fallback_tu: Option<clang::FallbackTranslationUnit>,
+
     /// Target information that can be useful for some stuff.
     target_info: clang::TargetInfo,
 
@@ -584,6 +587,7 @@ If you encounter an error missing from this list, please file an issue or a PR!"
             collected_typerefs: false,
             in_codegen: false,
             translation_unit,
+            fallback_tu: None,
             target_info,
             options,
             generated_bindgen_complex: Cell::new(false),
@@ -2060,6 +2064,21 @@ If you encounter an error missing from this list, please file an issue or a PR!"
         &self.translation_unit
     }
 
+    /// Initialize fallback translation unit
+    pub(crate) fn init_fallback_translation_unit(
+        &mut self,
+        fallback_tu: clang::FallbackTranslationUnit,
+    ) {
+        self.fallback_tu = Some(fallback_tu);
+    }
+
+    /// Initialize fallback translation unit
+    pub(crate) fn fallback_translation_unit_mut(
+        &mut self,
+    ) -> Option<&mut clang::FallbackTranslationUnit> {
+        self.fallback_tu.as_mut()
+    }
+
     /// Have we parsed the macro named `macro_name` already?
     pub(crate) fn parsed_macro(&self, macro_name: &[u8]) -> bool {
         self.parsed_macros.contains_key(macro_name)

bindgen/ir/var.rs

@@ -8,12 +8,15 @@ use super::int::IntKind;
 use super::item::Item;
 use super::ty::{FloatKind, TypeKind};
 use crate::callbacks::{ItemInfo, ItemKind, MacroParsingBehavior};
-use crate::clang;
 use crate::clang::ClangToken;
+use crate::clang::{self, FallbackTranslationUnit, TranslationUnit};
 use crate::parse::{ClangSubItemParser, ParseError, ParseResult};
 
+use std::fs::OpenOptions;
 use std::io;
+use std::io::Write;
 use std::num::Wrapping;
+use std::path::Path;
 
 /// The type for a constant variable.
 #[derive(Debug)]
@@ -389,9 +392,94 @@ impl ClangSubItemParser for Var {
     }
 }
 
+fn parse_macro_clang_fallback(
+    ctx: &mut BindgenContext,
+    cursor: &clang::Cursor,
+) -> Option<(Vec<u8>, cexpr::expr::EvalResult)> {
+    let file = ".macro_eval.c".to_string();
+    let contents = format!("int main() {{ {}; }}", cursor.spelling(),);
+
+    let root = if let Some(ftu) = ctx.fallback_translation_unit_mut() {
+        ftu.reparse(&[clang::UnsavedFile::new(&file, &contents)]);
+        ftu.translation_unit().cursor().collect_children()
+    } else {
+        let index = clang::Index::new(false, false);
+
+        let mut c_args = Vec::new();
+        for input_header in ctx.options().input_headers.iter() {
+            let path = Path::new(input_header.as_ref());
+            let header_name = path
+                .file_name()
+                .and_then(|hn| hn.to_str())
+                .map(|s| s.to_owned());
+            let header_path = path
+                .parent()
+                .and_then(|hp| hp.to_str())
+                .map(|s| s.to_owned());
+
+            if let (Some(hp), Some(hn)) = (header_path, header_name) {
+                let header_path = if hp.is_empty() {
+                    Path::new(".")
+                        .canonicalize()
+                        .map(|p| p.display().to_string())
+                        .unwrap_or(".".to_string())
+                } else {
+                    hp.clone()
+                };
+                let pch = format!("{header_path}/{hn}.pch");
+
+                if !Path::new(&pch).exists() {
+                    let header = format!("{header_path}/{hn}");
+                    let mut tu = TranslationUnit::parse(
+                        &index,
+                        &header,
+                        &[
+                            "-x".to_owned().into_boxed_str(),
+                            "c-header".to_owned().into_boxed_str(),
+                        ],
+                        &[],
+                        clang_sys::CXTranslationUnit_ForSerialization,
+                    )?;
+                    tu.save(&pch);
+                }
+
+                c_args.push("-include-pch".to_string().into_boxed_str());
+                c_args.push(pch.into_boxed_str());
+            }
+        }
+
+        OpenOptions::new()
+            .write(true)
+            .create(true)
+            .truncate(true)
+            .open(&file)
+            .ok()?
+            .write_all(contents.as_bytes())
+            .ok()?;
+
+        let f_translation_unit = FallbackTranslationUnit::new(&file, &c_args)?;
+        let root = f_translation_unit
+            .translation_unit()
+            .cursor()
+            .collect_children();
+        ctx.init_fallback_translation_unit(f_translation_unit);
+        root
+    };
+
+    let all_exprs = root.last()?.collect_children();
+    let paren = all_exprs.first()?.collect_children();
+
+    Some((
+        cursor.spelling().into_bytes(),
+        cexpr::expr::EvalResult::Int(Wrapping(
+            paren.first()?.evaluate()?.as_int()?,
+        )),
+    ))
+}
+
 /// Try and parse a macro using all the macros parsed until now.
 fn parse_macro(
-    ctx: &BindgenContext,
+    ctx: &mut BindgenContext,
     cursor: &clang::Cursor,
 ) -> Option<(Vec<u8>, cexpr::expr::EvalResult)> {
     use cexpr::expr;
@@ -402,6 +490,9 @@ fn parse_macro(
 
     match parser.macro_definition(&cexpr_tokens) {
         Ok((_, (id, val))) => Some((id.into(), val)),
+        _ if ctx.options().clang_macro_fallback => {
+            parse_macro_clang_fallback(ctx, cursor)
+        }
         _ => None,
     }
 }

bindgen/options/mod.rs

@@ -2104,5 +2104,20 @@ options! {
             }
         },
         as_args: "--emit-diagnostics",
+    },
+    /// Whether to use Clang evaluation on temporary files as a fallback for macros that fail to
+    /// parse.
+    clang_macro_fallback: bool {
+        methods: {
+            /// Use Clang as a fallback for macros that fail to parse using CExpr.
+            ///
+            /// This uses a workaround to evaluate each macro in a temporary file. Because this
+            /// results in slower compilation, this option is opt-in.
+            pub fn clang_macro_fallback(mut self) -> Self {
+                self.options.clang_macro_fallback = true;
+                self
+            }
+        },
+        as_args: "--clang-macro-fallback",
     }
 }