Use correct rustfmt for codegen

closes #1569

xtask/src/lib.rs

@@ -10,6 +10,7 @@ mod ast_src;
 use anyhow::Context;
 use std::{
     env, fs,
+    io::Write,
     path::{Path, PathBuf},
     process::{Command, Stdio},
 };
@@ -31,15 +32,7 @@ pub fn project_root() -> PathBuf {
 }
 
 pub fn run_rustfmt(mode: Mode) -> Result<()> {
-    match Command::new("rustup")
-        .args(&["run", TOOLCHAIN, "--", "cargo", "fmt", "--version"])
-        .stderr(Stdio::null())
-        .stdout(Stdio::null())
-        .status()
-    {
-        Ok(status) if status.success() => (),
-        _ => install_rustfmt().context("install rustfmt")?,
-    };
+    ensure_rustfmt()?;
 
     if mode == Mode::Verify {
         run(&format!("rustup run {} -- cargo fmt -- --check", TOOLCHAIN), ".")?;
@@ -49,7 +42,31 @@ pub fn run_rustfmt(mode: Mode) -> Result<()> {
     Ok(())
 }
 
-fn install_rustfmt() -> Result<()> {
+fn reformat(text: impl std::fmt::Display) -> Result<String> {
+    ensure_rustfmt()?;
+    let mut rustfmt = Command::new("rustup")
+        .args(&["run", TOOLCHAIN, "--", "rustfmt", "--config-path"])
+        .arg(project_root().join("rustfmt.toml"))
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .spawn()?;
+    write!(rustfmt.stdin.take().unwrap(), "{}", text)?;
+    let output = rustfmt.wait_with_output()?;
+    let stdout = String::from_utf8(output.stdout)?;
+    let preamble = "Generated file, do not edit by hand, see `crate/ra_tools/src/codegen`";
+    Ok(format!("//! {}\n\n{}", preamble, stdout))
+}
+
+fn ensure_rustfmt() -> Result<()> {
+    match Command::new("rustup")
+        .args(&["run", TOOLCHAIN, "--", "cargo", "fmt", "--version"])
+        .stderr(Stdio::null())
+        .stdout(Stdio::null())
+        .status()
+    {
+        Ok(status) if status.success() => return Ok(()),
+        _ => (),
+    };
     run(&format!("rustup toolchain install {}", TOOLCHAIN), ".")?;
     run(&format!("rustup component add rustfmt --toolchain {}", TOOLCHAIN), ".")
 }