Switch to single precompiled header in macro fallback

It appears that Clang only supports a single precompiled header at a
time. Because the macro fallback depends on the ability to provide
multiple precompiled headers at once, this commit changes the code to
include all provided headers into a single header to precompile and then
pass to the TranslationUnit. This should resolve the issue where the
macro fallback would not function as intended when multiple headers were
provided as input.

Author: jbaublitz

bindgen/clang.rs

@@ -1908,7 +1908,8 @@ impl Drop for TranslationUnit {
 /// Translation unit used for macro fallback parsing
 pub(crate) struct FallbackTranslationUnit {
     file_path: String,
-    pch_paths: Vec<String>,
+    header_path: String,
+    pch_path: String,
     idx: Box<Index>,
     tu: TranslationUnit,
 }
@@ -1923,7 +1924,8 @@ impl FallbackTranslationUnit {
     /// Create a new fallback translation unit
     pub(crate) fn new(
         file: String,
-        pch_paths: Vec<String>,
+        header_path: String,
+        pch_path: String,
         c_args: &[Box<str>],
     ) -> Option<Self> {
         // Create empty file
@@ -1944,7 +1946,8 @@ impl FallbackTranslationUnit {
         )?;
         Some(FallbackTranslationUnit {
             file_path: file,
-            pch_paths,
+            header_path,
+            pch_path,
             tu: f_translation_unit,
             idx: f_index,
         })
@@ -1982,9 +1985,8 @@ impl FallbackTranslationUnit {
 impl Drop for FallbackTranslationUnit {
     fn drop(&mut self) {
         let _ = std::fs::remove_file(&self.file_path);
-        for pch in self.pch_paths.iter() {
-            let _ = std::fs::remove_file(pch);
-        }
+        let _ = std::fs::remove_file(&self.header_path);
+        let _ = std::fs::remove_file(&self.pch_path);
     }
 }
 

bindgen/ir/context.rs

@@ -29,6 +29,8 @@ use quote::ToTokens;
 use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::collections::{BTreeSet, HashMap as StdHashMap};
+use std::fs::OpenOptions;
+use std::io::Write;
 use std::mem;
 use std::path::Path;
 
@@ -2081,55 +2083,79 @@ If you encounter an error missing from this list, please file an issue or a PR!"
 
             let index = clang::Index::new(false, false);
 
-            let mut c_args = Vec::new();
-            let mut pch_paths = Vec::new();
-            for input_header in self.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());
-
-                let (header, pch) = if let (Some(ref hp), Some(hn)) =
-                    (header_path, header_name)
-                {
-                    let header_path = if hp.is_empty() { "." } else { hp };
-                    let header = format!("{header_path}/{hn}");
-                    let pch_path = if let Some(ref path) =
-                        self.options().clang_macro_fallback_build_dir
-                    {
-                        path.as_os_str().to_str()?
-                    } else {
-                        header_path
-                    };
-                    (header, format!("{pch_path}/{hn}.pch"))
-                } else {
-                    return None;
-                };
-
-                let mut tu = clang::TranslationUnit::parse(
-                    &index,
-                    &header,
-                    &[
-                        "-x".to_owned().into_boxed_str(),
-                        "c-header".to_owned().into_boxed_str(),
-                    ],
-                    &[],
-                    clang_sys::CXTranslationUnit_ForSerialization,
+            let (header_names, header_paths, header_contents) =
+                self.options.input_headers.iter().try_fold(
+                    (Vec::new(), Vec::new(), String::new()),
+                    |(
+                        mut header_names_to_compile,
+                        mut header_paths,
+                        mut header_contents,
+                    ),
+                     next| {
+                        let path = Path::new(next.as_ref());
+                        if let Some(header_path) = path.parent() {
+                            header_paths
+                                .push(header_path.as_os_str().to_str()?);
+                        } else {
+                            header_paths.push(".");
+                        }
+                        let header_name = path.file_name()?.to_str()?;
+                        header_names_to_compile
+                            .push(header_name.split(".h").next()?.to_string());
+                        header_contents +=
+                            format!("\n#include <{header_name}>").as_str();
+                        Some((
+                            header_names_to_compile,
+                            header_paths,
+                            header_contents,
+                        ))
+                    },
                 )?;
-                tu.save(&pch).ok()?;
+            let header_to_precompile = format!(
+                "{}/{}",
+                match self.options().clang_macro_fallback_build_dir {
+                    Some(ref path) => path.as_os_str().to_str()?,
+                    None => ".",
+                },
+                header_names.join("-") + ".h"
+            );
+            let pch = header_to_precompile.clone() + ".pch";
+
+            let mut header_to_precompile_file = OpenOptions::new()
+                .create(true)
+                .truncate(true)
+                .write(true)
+                .open(&header_to_precompile)
+                .ok()?;
+            header_to_precompile_file
+                .write_all(header_contents.as_bytes())
+                .ok()?;
 
-                c_args.push("-include-pch".to_string().into_boxed_str());
-                c_args.push(pch.clone().into_boxed_str());
-                pch_paths.push(pch);
+            let mut c_args = Vec::new();
+            c_args.push("-x".to_string().into_boxed_str());
+            c_args.push("c-header".to_string().into_boxed_str());
+            for header_path in header_paths {
+                c_args.push("-I".to_string().into_boxed_str());
+                c_args.push(header_path.to_string().into_boxed_str());
             }
-
+            let mut tu = clang::TranslationUnit::parse(
+                &index,
+                &header_to_precompile,
+                &c_args,
+                &[],
+                clang_sys::CXTranslationUnit_ForSerialization,
+            )?;
+            tu.save(&pch).ok()?;
+
+            let c_args = vec![
+                "-include-pch".to_string().into_boxed_str(),
+                pch.clone().into_boxed_str(),
+            ];
             self.fallback_tu = Some(clang::FallbackTranslationUnit::new(
-                file, pch_paths, &c_args,
+                file,
+                header_to_precompile,
+                pch,
+                &c_args,
             )?);
         }