Allow running multiple transpiles in parallel (#1241)

If c2rust-transpile needs to generate a temporary compile_commands.json,
previously it used a fixed path for it across all invocations. Instead,
create a uniquely-named temporary directory for it, so that parallel
transpiles don't clobber each other.

I've used a two-year-old release of tempfile to avoid adding a bunch of
duplicate versions of other crates to Cargo.lock, but presumably some
upgrades ought to happen sooner or later.

Author: kkysen

Cargo.lock

@@ -37,6 +37,7 @@ smallvec = "1.0"
 strum = "0.24"
 strum_macros = "0.24"
 syn = { version = "1.0", features = ["full", "extra-traits", "parsing", "printing"]}
+tempfile = "3.5.0"
 
 [features]
 # Force static linking of LLVM

c2rust-transpile/Cargo.toml

@@ -25,6 +25,7 @@ use itertools::Itertools;
 use log::{info, warn};
 use regex::Regex;
 use serde_derive::Serialize;
+pub use tempfile::TempDir;
 
 use crate::c_ast::Printer;
 use crate::c_ast::*;
@@ -226,8 +227,18 @@ fn get_module_name(
     file.to_str().map(String::from)
 }
 
-pub fn create_temp_compile_commands(sources: &[PathBuf]) -> PathBuf {
-    let temp_path = std::env::temp_dir().join("compile_commands.json");
+pub fn create_temp_compile_commands(sources: &[PathBuf]) -> (TempDir, PathBuf) {
+    // If we generate the same path here on every run, then we can't run
+    // multiple transpiles in parallel, so we need a unique path. But clang
+    // won't read this file unless it is named exactly "compile_commands.json",
+    // so we can't change the filename. Instead, create a temporary directory
+    // with a unique name, and put the file there.
+    let temp_dir = tempfile::Builder::new()
+        .prefix("c2rust-")
+        .tempdir()
+        .expect("Failed to create temporary directory for compile_commands.json");
+    let temp_path = temp_dir.path().join("compile_commands.json");
+
     let compile_commands: Vec<CompileCmd> = sources
         .iter()
         .map(|source_file| {
@@ -252,8 +263,7 @@ pub fn create_temp_compile_commands(sources: &[PathBuf]) -> PathBuf {
         File::create(&temp_path).expect("Failed to create temporary compile_commands.json");
     file.write_all(json_content.as_bytes())
         .expect("Failed to write to temporary compile_commands.json");
-
-    temp_path
+    (temp_dir, temp_path)
 }
 
 /// Main entry point to transpiler. Called from CLI tools with the result of

c2rust-transpile/src/lib.rs

@@ -1,7 +1,7 @@
 use clap::{Parser, ValueEnum};
 use log::LevelFilter;
 use regex::Regex;
-use std::{fs, path::PathBuf};
+use std::{ffi::OsStr, fs, path::PathBuf};
 
 use c2rust_transpile::{Diagnostic, ReplaceMode, TranspilerConfig};
 
@@ -226,28 +226,29 @@ fn main() {
         tcfg.emit_modules = true
     };
 
-    let mut created_temp_compile_commands = false;
+    let mut temp_compile_commands_dir = None;
 
-    let compile_commands = if args.compile_commands.len() == 1
-        && args.compile_commands[0].extension() == Some(std::ffi::OsStr::new("json"))
+    let compile_commands = if args
+        .compile_commands
+        .iter()
+        .any(|path| path.extension() == Some(OsStr::new("json")))
     {
+        if args.compile_commands.len() != 1 {
+            // More than one file provided and at least one is a JSON file
+            panic!("Compile commands JSON and multiple sources provided.
+                Exactly one compile_commands.json file should be provided, or a list of source files, but not both.");
+        }
         // Only one file provided and it's a JSON file
         match fs::canonicalize(&args.compile_commands[0]) {
             Ok(canonical_path) => canonical_path,
             Err(e) => panic!("Failed to canonicalize path: {:?}", e),
         }
-    } else if args
-        .compile_commands
-        .iter()
-        .any(|path| path.extension() == Some(std::ffi::OsStr::new("json")))
-    {
-        // More than one file provided and at least one is a JSON file
-        panic!("Compile commands JSON and multiple sources provided.
-                Exactly one compile_commands.json file should be provided, or a list of source files, but not both.");
     } else {
         // Handle as a list of source files
-        created_temp_compile_commands = true;
-        c2rust_transpile::create_temp_compile_commands(&args.compile_commands)
+        let (temp_dir, temp_path) =
+            c2rust_transpile::create_temp_compile_commands(&args.compile_commands);
+        temp_compile_commands_dir = Some(temp_dir);
+        temp_path
     };
 
     let extra_args = args
@@ -259,8 +260,8 @@ fn main() {
     c2rust_transpile::transpile(tcfg, &compile_commands, &extra_args);
 
     // Remove the temporary compile_commands.json if it was created
-    if created_temp_compile_commands {
-        std::fs::remove_file(&compile_commands)
+    if let Some(temp) = temp_compile_commands_dir {
+        temp.close()
             .expect("Failed to remove temporary compile_commands.json");
     }
 }