common/token_stream_printer.rs - crubit - Git at Google

 // Part of the Crubit project, under the Apache License v2.0 with LLVM
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

 use anyhow::{bail, Result};
 use proc_macro2::{Delimiter, TokenStream, TokenTree};
 use std::ffi::{OsStr, OsString};
 use std::io::Write as _;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};

 // TODO(b/231320237): The `RustfmtConfig` struct should be replaced with
 // `rustfmt_nightly::Config` once we switch to using rustfmt as a library
 // (instead of invoking the `rustfmt` executable).
 pub struct RustfmtConfig {
     /// Path to the `rustfmt` executable.
     exe_path: PathBuf,

     /// Cmdline arguments to be passed to the `rustfmt` executable.
     cmdline_args: Vec<OsString>,
 }

 pub const RUSTFMT_EXE_PATH_FOR_TESTING: &str =
     "third_party/crosstool/rust/unstable/main_sysroot/bin/rustfmt";

 pub const CLANG_FORMAT_EXE_PATH_FOR_TESTING: &str =
     "third_party/crosstool/google3_users/clang-format";

 impl RustfmtConfig {
     /// Creates a config that will invoke `rustfmt` at the given
     /// `rustfmt_exe_path`.  If `rustfmt_config_path` is specified, then a
     /// `rustfmt.toml` file at that path will be used to configure the
     /// formatting details;  otherwise a default formatting will be used.
     pub fn new(rustfmt_exe_path: &Path, rustfmt_config_path: Option<&Path>) -> Self {
         Self {
             exe_path: rustfmt_exe_path.to_path_buf(),
             cmdline_args: match rustfmt_config_path {
                 None => Self::default_cmdline_args(),
                 Some(path) => Self::cmdline_args_with_custom_config_path(path),
             },
         }
     }

     fn for_testing() -> Self {
         Self {
             exe_path: PathBuf::from(RUSTFMT_EXE_PATH_FOR_TESTING),
             cmdline_args: Self::default_cmdline_args(),
         }
     }

     fn cmdline_args_with_custom_config_path(rustfmt_config_path: &Path) -> Vec<OsString> {
         let mut config_path_arg: OsString = "--config-path=".into();
         config_path_arg.push(rustfmt_config_path);
         Self::append_config_overrides(vec![config_path_arg])
     }

     fn default_cmdline_args() -> Vec<OsString> {
         Self::append_config_overrides(vec!["--edition=2021".into(), "--config=version=Two".into()])
     }

     fn append_config_overrides(mut cmdline_args: Vec<OsString>) -> Vec<OsString> {
         cmdline_args.extend(vec![
             // We are representing doc comments as attributes in the token stream and use rustfmt
             // to unpack them again.
             "--config=normalize_doc_attributes=true".into(),
             // We don't want rustfmt to reflow C++ doc comments, so we turn off wrapping globally
             // and reflow generated comments manually.
             "--config=wrap_comments=false".into(),
         ]);
         cmdline_args
     }
 }

 /// Like `tokens_to_string` but also runs the result through `rustfmt`.
 pub fn rs_tokens_to_formatted_string(
     tokens: TokenStream,
     config: &RustfmtConfig,
 ) -> Result<String> {
     rustfmt(tokens_to_string(tokens)?, config)
 }

 /// Like `rs_tokens_to_formatted_string`, but always using a Crubit-internal,
 /// default rustfmt config.  This should only be called by tests - product code
 /// should support custom `rustfmt.toml` and take the path to `rustfmt` binary
 /// as a cmdline argument.
 pub fn rs_tokens_to_formatted_string_for_tests(input: TokenStream) -> Result<String> {
     rs_tokens_to_formatted_string(input, &RustfmtConfig::for_testing())
 }

 /// Like `tokens_to_string` but also runs the result through `clang-format`.
 pub fn cc_tokens_to_formatted_string(
     tokens: TokenStream,
     clang_format_exe_path: &Path,
 ) -> Result<String> {
     clang_format(tokens_to_string(tokens)?, clang_format_exe_path)
 }

 /// Like `cc_tokens_to_formatted_string`, but always using a hardcoded path to
 /// where the `clang-format` binary is in Crubit's test environment.  This
 /// should only be called by tests - product code should take the path to the
 /// `clang-format` binary as a cmdline argument.
 pub fn cc_tokens_to_formatted_string_for_tests(tokens: TokenStream) -> Result<String> {
     clang_format(tokens_to_string(tokens)?, Path::new(CLANG_FORMAT_EXE_PATH_FOR_TESTING))
 }

 /// Produces source code out of the token stream.
 ///
 /// Notable features:
 /// * quote! cannot produce a single `#` token (that is not immediately followed
 ///   by `(`, `[`, `{`, or variable interpolation). For cases when we need `#`
 ///   to be produced in the C++ source code use the placeholder
 ///   `__HASH_TOKEN__`.
 /// * The Rust tokenizer ignores newlines as they are not significant for Rust.
 ///   For C++ they are (for example there needs to be a newline after `#include
 ///   "foo/bar.h"`). We are also using explict newlines for making the generated
 ///   Rust/C++ source code more readable. Use the placeholder `__NEWLINE__` to
 ///   insert a newline character.
 /// * `TokenStream` cannot encode formatting whitespace, so we use the
 ///   placeholder `__SPACE__`.
 /// * `TokenStream` cannot encode comments, so we use the placeholder
 ///   `__COMMENT__`, followed by a string literal.
 pub fn write_unformatted_tokens(
     result: &mut impl std::fmt::Write,
     tokens: TokenStream,
 ) -> Result<()> {
     let mut it = tokens.into_iter().peekable();
     let mut tt_prev = None;
     while let Some(tt) = it.next() {
         match tt {
             TokenTree::Ident(ref tt) if tt == "__NEWLINE__" => writeln!(result)?,
             TokenTree::Ident(ref tt) if tt == "__SPACE__" => write!(result, " ")?,
             TokenTree::Ident(ref tt) if tt == "__HASH_TOKEN__" => write!(result, "#")?,

             TokenTree::Ident(ref tt) if tt == "__COMMENT__" => {
                 if let Some(TokenTree::Literal(lit)) = it.next() {
                     writeln!(
                         result,
                         "// {}",
                         lit.to_string().trim_matches('"').replace("\\n", "\n// ")
                     )?;
                 } else {
                     bail!("__COMMENT__ must be followed by a literal")
                 }
             }
             TokenTree::Group(ref tt) => {
                 let (open_delimiter, closed_delimiter) = match tt.delimiter() {
                     Delimiter::Parenthesis => ("(", ")"),
                     Delimiter::Bracket => ("[", "]"),
                     Delimiter::Brace => ("{ ", " }"),
                     Delimiter::None => ("", ""),
                 };
                 write!(result, "{}", open_delimiter)?;
                 write_unformatted_tokens(result, tt.stream())?;
                 write!(result, "{}", closed_delimiter)?;
             }
             _ => {
                 write!(result, "{}", tt)?;

                 // Insert spaces between tokens when they are needed to separate tokens.
                 // In particular, `a b` is different than `ab`, and `: ::` is different from
                 // `:::`.
                 if let Some(tt_next) = it.peek() {
                     if tokens_require_whitespace(tt_prev.as_ref(), &tt, tt_next) {
                         write!(result, " ")?;
                     }
                 }
             }
         }
         tt_prev = Some(tt);
     }
     Ok(())
 }

 fn tokens_to_string(tokens: TokenStream) -> Result<String> {
     let mut result = String::new();
     write_unformatted_tokens(&mut result, tokens)?;
     Ok(result)
 }

 /// Returns true if `current` and `next` should have whitespace between them,
 /// and false if they should not.
 ///
 /// For example, `a b` is different than `ab`, and `: ::` is different from
 /// `:::`.
 fn tokens_require_whitespace(
     prev: Option<&TokenTree>,
     current: &TokenTree,
     next: &TokenTree,
 ) -> bool {
     if is_ident_or_literal(current) && is_ident_or_literal(next) {
         return true;
     }

     // We (currently) only add a space for `:`.
     // A lone `:` always gets a space after it. A lone `::` doesn't.
     // So if the current character is a colon, it gets a space after it if it is not
     // the start or end of a `::`.
     fn get_colon(tt: &TokenTree) -> Option<&proc_macro2::Punct> {
         let TokenTree::Punct(p) = tt else {
             return None;
         };
         if p.as_char() != ':' {
             return None;
         }
         Some(p)
     }

     let Some(current_colon) = get_colon(current) else {
         return false;
     };
     if current_colon.spacing() == proc_macro2::Spacing::Joint {
         // This is the first `:` in `::`
         return false;
     }
     match prev.and_then(get_colon) {
         // this is the second `:` in `::`
         Some(prev_colon) if prev_colon.spacing() == proc_macro2::Spacing::Joint => {
             // a `::` shouldn't have a space after it, generally, but we add one if the next
             // token is a `:` because otherwise it looks awful.
             get_colon(next).is_some()
         }
         // this is a standalone `:`.
         _ => true,
     }
 }

 fn is_ident_or_literal(tt: &TokenTree) -> bool {
     match tt {
         TokenTree::Ident(id) => id != "__NEWLINE__" && id != "__SPACE__",
         TokenTree::Literal(_) => true,
         _ => false,
     }
 }

 fn pipe_string_through_process<'a>(
     input: String,
     exe_name: &str,
     exe_path: &Path,
     args: impl IntoIterator<Item = &'a OsStr>,
 ) -> Result<String> {
     let mut child = Command::new(exe_path)
         .args(args.into_iter())
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
         .stderr(Stdio::piped())
         .spawn()
         .unwrap_or_else(|e| panic!("Failed to spawn {exe_name} at {exe_path:?}: {e}"));

     let mut stdin = child.stdin.take().expect("Failed to open {exe_name} stdin");
     let handle = std::thread::spawn(move || {
         stdin.write_all(input.as_bytes()).expect("Failed to write to {exe_name} stdin");
     });
     let output = child.wait_with_output().expect("Failed to read {exe_name} stdout");

     handle.join().unwrap();

     if !output.status.success() {
         bail!("{exe_name} reported an error: {}", String::from_utf8_lossy(&output.stderr));
     }

     Ok(String::from_utf8_lossy(&output.stdout).to_string())
 }

 fn rustfmt(input: String, config: &RustfmtConfig) -> Result<String> {
     pipe_string_through_process(
         input,
         "rustfmt",
         &config.exe_path,
         config.cmdline_args.iter().map(OsString::as_os_str),
     )
 }

 fn clang_format(input: String, clang_format_exe_path: &Path) -> Result<String> {
     pipe_string_through_process(
         input,
         "clang-format",
         clang_format_exe_path,
         [OsStr::new("--style=google")],
     )
 }

 #[cfg(test)]
 mod tests {
     use super::*;

     use super::Result;
     use quote::quote;
     use tempfile::tempdir;

     #[test]
     fn test_simple_token_stream() -> Result<()> {
         let token_stream = quote! {
           struct Foo {}

           impl Bar for Foo {
             fn bar(&self) {}
           }
         };
         assert_eq!(
             tokens_to_string(token_stream)?,
             "struct Foo{  }impl Bar for Foo{ fn bar(&self){  } }"
         );
         Ok(())
     }

     #[test]
     fn test_space_idents_and_literals() -> Result<()> {
         let token_stream = quote! { foo 42 bar 23 };
         assert_eq!(tokens_to_string(token_stream)?, "foo 42 bar 23");
         Ok(())
     }

     #[test]
     fn test_dont_space_punctuation() -> Result<()> {
         let token_stream = quote! { foo+42+bar+23 };
         assert_eq!(tokens_to_string(token_stream)?, "foo+42+bar+23");
         Ok(())
     }

     /// `foo : ::bar` is valid syntax, but `foo:::bar` is not.
     #[test]
     fn test_paamayim_nekudotayim() -> Result<()> {
         assert_eq!(tokens_to_string(quote! { x : :: y })?, "x: ::y");
         // The following variants are not syntactically valid, but good to have working
         // anyway.
         assert_eq!(tokens_to_string(quote! { x : : y })?, "x: : y");
         assert_eq!(tokens_to_string(quote! { x :: :: y })?, "x:: ::y");
         assert_eq!(tokens_to_string(quote! { x :: : y })?, "x:: : y");
         Ok(())
     }

     #[test]
     fn test_newline_token() -> Result<()> {
         let token_stream = quote! { a __NEWLINE__ b };
         assert_eq!(tokens_to_string(token_stream)?, "a\nb");
         Ok(())
     }

     #[test]
     fn test_space_token() -> Result<()> {
         let token_stream = quote! { a __SPACE__ = __SPACE__ b };
         assert_eq!(tokens_to_string(token_stream)?, "a = b");
         Ok(())
     }

     #[test]
     fn test_redundant_space_token() -> Result<()> {
         let token_stream = quote! { a __SPACE__ b };
         assert_eq!(tokens_to_string(token_stream)?, "a b");
         Ok(())
     }

     #[test]
     fn test_hash_token() -> Result<()> {
         let token_stream = quote! { a __HASH_TOKEN__ b };
         assert_eq!(tokens_to_string(token_stream)?, "a #b");
         Ok(())
     }

     #[test]
     fn test_include_standard_header() -> Result<()> {
         let token_stream = quote! { __HASH_TOKEN__ include <cstddef> };
         assert_eq!(tokens_to_string(token_stream)?, "#include<cstddef>");
         Ok(())
     }

     #[test]
     fn test_comments() -> Result<()> {
         let token_stream = quote! { __COMMENT__ "line1\nline2" };
         assert_eq!(tokens_to_string(token_stream)?, "// line1\n// line2\n");
         Ok(())
     }

     #[test]
     fn test_invalid_comment() -> Result<()> {
         assert!(tokens_to_string(quote! { __COMMENT__ }).is_err());
         assert!(tokens_to_string(quote! { __COMMENT__ ident }).is_err());
         Ok(())
     }

     #[test]
     fn test_doc_comment() -> Result<()> {
         // token_stream_printer (and rustfmt) don't put a space between /// and the doc
         // comment, if the space is desired, it has to appear in the annotation.
         assert_eq!(
             rs_tokens_to_formatted_string_for_tests(quote! { #[doc = "hello"] struct X {} })?,
             "///hello\nstruct X {}\n"
         );
         assert_eq!(
             rs_tokens_to_formatted_string_for_tests(
                 quote! { #[doc = "hello\nworld"] struct X {} }
             )?,
             "///hello\n///world\nstruct X {}\n"
         );
         Ok(())
     }

     #[test]
     fn test_doc_comment_leading_spaces() -> Result<()> {
         assert_eq!(
             rs_tokens_to_formatted_string_for_tests(quote! { #[doc = " hello"] struct X {} })?,
             "/// hello\nstruct X {}\n"
         );
         assert_eq!(
             rs_tokens_to_formatted_string_for_tests(
                 quote! { #[doc = " hello\n world"] struct X {} }
             )?,
             "/// hello\n/// world\nstruct X {}\n"
         );
         Ok(())
     }

     #[test]
     fn test_special_tokens_in_groups() -> Result<()> {
         assert_eq!(tokens_to_string(quote! {{ a __NEWLINE__ b }})?, "{ a\nb }");
         assert_eq!(tokens_to_string(quote! {{ a __SPACE__ b }})?, "{ a b }");
         assert_eq!(tokens_to_string(quote! {(a __COMMENT__ "b")})?, "(a // b\n)");
         assert_eq!(tokens_to_string(quote! {[__HASH_TOKEN__ a]})?, "[#a]");
         Ok(())
     }

     #[test]
     fn test_rs_tokens_to_formatted_string_for_tests() {
         let input = quote! {
             fn foo() {}
             fn bar() {}
         };
         let output = rs_tokens_to_formatted_string_for_tests(input).unwrap();
         assert_eq!(
             output,
             r#"fn foo() {}
 fn bar() {}
 "#
         );
     }

     #[test]
     fn test_rs_tokens_to_formatted_string() {
         let cfg = RustfmtConfig::new(Path::new(RUSTFMT_EXE_PATH_FOR_TESTING), None);
         let input = quote! {
             fn bar() {}
             fn foo(x: i32, y: i32) -> i32 { x + y }
         };
         let output = rs_tokens_to_formatted_string(input, &cfg).unwrap();
         assert_eq!(
             output,
             r#"fn bar() {}
 fn foo(x: i32, y: i32) -> i32 {
     x + y
 }
 "#
         );
     }

     #[test]
     fn test_rs_tokens_to_formatted_string_with_custom_rustfmt_toml() -> Result<()> {
         let tmpdir = tempdir()?;
         let rustfmt_toml_path = tmpdir.path().join("rustfmt-for-tests.toml");
         std::fs::write(
             &rustfmt_toml_path,
             r#" edition = "2021"
                 version = "Two"
                 fn_args_layout="Vertical" "#,
         )?;
         let cfg =
             RustfmtConfig::new(Path::new(RUSTFMT_EXE_PATH_FOR_TESTING), Some(&rustfmt_toml_path));
         let input = quote! {
             fn bar() {}
             fn foo(x: i32, y: i32) -> i32 { x + y }
         };

         let output = rs_tokens_to_formatted_string(input, &cfg).unwrap();
         assert_eq!(
             output,
             r#"fn bar() {}
 fn foo(
     x: i32,
     y: i32,
 ) -> i32 {
     x + y
 }
 "#
         );
         Ok(())
     }

     #[test]
     fn test_cc_tokens_to_formatted_string_for_tests() {
         let input = quote! {
             namespace ns {
             void foo() {}
             void bar() {}
             }
         };
         let output = cc_tokens_to_formatted_string_for_tests(input).unwrap();
         assert_eq!(
             output,
             r#"namespace ns {
 void foo() {}
 void bar() {}
 }  // namespace ns"#
         );
     }
 }
	// Part of the Crubit project, under the Apache License v2.0 with LLVM
	// Exceptions. See /LICENSE for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

	use anyhow::{bail, Result};
	use proc_macro2::{Delimiter, TokenStream, TokenTree};
	use std::ffi::{OsStr, OsString};
	use std::io::Write as _;
	use std::path::{Path, PathBuf};
	use std::process::{Command, Stdio};

	// TODO(b/231320237): The `RustfmtConfig` struct should be replaced with
	// `rustfmt_nightly::Config` once we switch to using rustfmt as a library
	// (instead of invoking the `rustfmt` executable).
	pub struct RustfmtConfig {
	/// Path to the `rustfmt` executable.
	exe_path: PathBuf,

	/// Cmdline arguments to be passed to the `rustfmt` executable.
	cmdline_args: Vec<OsString>,
	}

	pub const RUSTFMT_EXE_PATH_FOR_TESTING: &str =
	"third_party/crosstool/rust/unstable/main_sysroot/bin/rustfmt";

	pub const CLANG_FORMAT_EXE_PATH_FOR_TESTING: &str =
	"third_party/crosstool/google3_users/clang-format";

	impl RustfmtConfig {
	/// Creates a config that will invoke `rustfmt` at the given
	/// `rustfmt_exe_path`. If `rustfmt_config_path` is specified, then a
	/// `rustfmt.toml` file at that path will be used to configure the
	/// formatting details; otherwise a default formatting will be used.
	pub fn new(rustfmt_exe_path: &Path, rustfmt_config_path: Option<&Path>) -> Self {
	Self {
	exe_path: rustfmt_exe_path.to_path_buf(),
	cmdline_args: match rustfmt_config_path {
	None => Self::default_cmdline_args(),
	Some(path) => Self::cmdline_args_with_custom_config_path(path),
	},
	}
	}

	fn for_testing() -> Self {
	Self {
	exe_path: PathBuf::from(RUSTFMT_EXE_PATH_FOR_TESTING),
	cmdline_args: Self::default_cmdline_args(),
	}
	}

	fn cmdline_args_with_custom_config_path(rustfmt_config_path: &Path) -> Vec<OsString> {
	let mut config_path_arg: OsString = "--config-path=".into();
	config_path_arg.push(rustfmt_config_path);
	Self::append_config_overrides(vec![config_path_arg])
	}

	fn default_cmdline_args() -> Vec<OsString> {
	Self::append_config_overrides(vec!["--edition=2021".into(), "--config=version=Two".into()])
	}

	fn append_config_overrides(mut cmdline_args: Vec<OsString>) -> Vec<OsString> {
	cmdline_args.extend(vec![
	// We are representing doc comments as attributes in the token stream and use rustfmt
	// to unpack them again.
	"--config=normalize_doc_attributes=true".into(),
	// We don't want rustfmt to reflow C++ doc comments, so we turn off wrapping globally
	// and reflow generated comments manually.
	"--config=wrap_comments=false".into(),
	]);
	cmdline_args
	}
	}

	/// Like `tokens_to_string` but also runs the result through `rustfmt`.
	pub fn rs_tokens_to_formatted_string(
	tokens: TokenStream,
	config: &RustfmtConfig,
	) -> Result<String> {
	rustfmt(tokens_to_string(tokens)?, config)
	}

	/// Like `rs_tokens_to_formatted_string`, but always using a Crubit-internal,
	/// default rustfmt config. This should only be called by tests - product code
	/// should support custom `rustfmt.toml` and take the path to `rustfmt` binary
	/// as a cmdline argument.
	pub fn rs_tokens_to_formatted_string_for_tests(input: TokenStream) -> Result<String> {
	rs_tokens_to_formatted_string(input, &RustfmtConfig::for_testing())
	}

	/// Like `tokens_to_string` but also runs the result through `clang-format`.
	pub fn cc_tokens_to_formatted_string(
	tokens: TokenStream,
	clang_format_exe_path: &Path,
	) -> Result<String> {
	clang_format(tokens_to_string(tokens)?, clang_format_exe_path)
	}

	/// Like `cc_tokens_to_formatted_string`, but always using a hardcoded path to
	/// where the `clang-format` binary is in Crubit's test environment. This
	/// should only be called by tests - product code should take the path to the
	/// `clang-format` binary as a cmdline argument.
	pub fn cc_tokens_to_formatted_string_for_tests(tokens: TokenStream) -> Result<String> {
	clang_format(tokens_to_string(tokens)?, Path::new(CLANG_FORMAT_EXE_PATH_FOR_TESTING))
	}

	/// Produces source code out of the token stream.
	///
	/// Notable features:
	/// * quote! cannot produce a single `#` token (that is not immediately followed
	/// by `(`, `[`, `{`, or variable interpolation). For cases when we need `#`
	/// to be produced in the C++ source code use the placeholder
	/// `__HASH_TOKEN__`.
	/// * The Rust tokenizer ignores newlines as they are not significant for Rust.
	/// For C++ they are (for example there needs to be a newline after `#include
	/// "foo/bar.h"`). We are also using explict newlines for making the generated
	/// Rust/C++ source code more readable. Use the placeholder `__NEWLINE__` to
	/// insert a newline character.
	/// * `TokenStream` cannot encode formatting whitespace, so we use the
	/// placeholder `__SPACE__`.
	/// * `TokenStream` cannot encode comments, so we use the placeholder
	/// `__COMMENT__`, followed by a string literal.
	pub fn write_unformatted_tokens(
	result: &mut impl std::fmt::Write,
	tokens: TokenStream,
	) -> Result<()> {
	let mut it = tokens.into_iter().peekable();
	let mut tt_prev = None;
	while let Some(tt) = it.next() {
	match tt {
	TokenTree::Ident(ref tt) if tt == "__NEWLINE__" => writeln!(result)?,
	TokenTree::Ident(ref tt) if tt == "__SPACE__" => write!(result, " ")?,
	TokenTree::Ident(ref tt) if tt == "__HASH_TOKEN__" => write!(result, "#")?,

	TokenTree::Ident(ref tt) if tt == "__COMMENT__" => {
	if let Some(TokenTree::Literal(lit)) = it.next() {
	writeln!(
	result,
	"// {}",
	lit.to_string().trim_matches('"').replace("\\n", "\n// ")
	)?;
	} else {
	bail!("__COMMENT__ must be followed by a literal")
	}
	}
	TokenTree::Group(ref tt) => {
	let (open_delimiter, closed_delimiter) = match tt.delimiter() {
	Delimiter::Parenthesis => ("(", ")"),
	Delimiter::Bracket => ("[", "]"),
	Delimiter::Brace => ("{ ", " }"),
	Delimiter::None => ("", ""),
	};
	write!(result, "{}", open_delimiter)?;
	write_unformatted_tokens(result, tt.stream())?;
	write!(result, "{}", closed_delimiter)?;
	}
	_ => {
	write!(result, "{}", tt)?;

	// Insert spaces between tokens when they are needed to separate tokens.
	// In particular, `a b` is different than `ab`, and `: ::` is different from
	// `:::`.
	if let Some(tt_next) = it.peek() {
	if tokens_require_whitespace(tt_prev.as_ref(), &tt, tt_next) {
	write!(result, " ")?;
	}
	}
	}
	}
	tt_prev = Some(tt);
	}
	Ok(())
	}

	fn tokens_to_string(tokens: TokenStream) -> Result<String> {
	let mut result = String::new();
	write_unformatted_tokens(&mut result, tokens)?;
	Ok(result)
	}

	/// Returns true if `current` and `next` should have whitespace between them,
	/// and false if they should not.
	///
	/// For example, `a b` is different than `ab`, and `: ::` is different from
	/// `:::`.
	fn tokens_require_whitespace(
	prev: Option<&TokenTree>,
	current: &TokenTree,
	next: &TokenTree,
	) -> bool {
	if is_ident_or_literal(current) && is_ident_or_literal(next) {
	return true;
	}

	// We (currently) only add a space for `:`.
	// A lone `:` always gets a space after it. A lone `::` doesn't.
	// So if the current character is a colon, it gets a space after it if it is not
	// the start or end of a `::`.
	fn get_colon(tt: &TokenTree) -> Option<&proc_macro2::Punct> {
	let TokenTree::Punct(p) = tt else {
	return None;
	};
	if p.as_char() != ':' {
	return None;
	}
	Some(p)
	}

	let Some(current_colon) = get_colon(current) else {
	return false;
	};
	if current_colon.spacing() == proc_macro2::Spacing::Joint {
	// This is the first `:` in `::`
	return false;
	}
	match prev.and_then(get_colon) {
	// this is the second `:` in `::`
	Some(prev_colon) if prev_colon.spacing() == proc_macro2::Spacing::Joint => {
	// a `::` shouldn't have a space after it, generally, but we add one if the next
	// token is a `:` because otherwise it looks awful.
	get_colon(next).is_some()
	}
	// this is a standalone `:`.
	_ => true,
	}
	}

	fn is_ident_or_literal(tt: &TokenTree) -> bool {
	match tt {
	TokenTree::Ident(id) => id != "__NEWLINE__" && id != "__SPACE__",
	TokenTree::Literal(_) => true,
	_ => false,
	}
	}

	fn pipe_string_through_process<'a>(
	input: String,
	exe_name: &str,
	exe_path: &Path,
	args: impl IntoIterator<Item = &'a OsStr>,
	) -> Result<String> {
	let mut child = Command::new(exe_path)
	.args(args.into_iter())
	.stdin(Stdio::piped())
	.stdout(Stdio::piped())
	.stderr(Stdio::piped())
	.spawn()
	.unwrap_or_else(\|e\| panic!("Failed to spawn {exe_name} at {exe_path:?}: {e}"));

	let mut stdin = child.stdin.take().expect("Failed to open {exe_name} stdin");
	let handle = std::thread::spawn(move \|\| {
	stdin.write_all(input.as_bytes()).expect("Failed to write to {exe_name} stdin");
	});
	let output = child.wait_with_output().expect("Failed to read {exe_name} stdout");

	handle.join().unwrap();

	if !output.status.success() {
	bail!("{exe_name} reported an error: {}", String::from_utf8_lossy(&output.stderr));
	}

	Ok(String::from_utf8_lossy(&output.stdout).to_string())
	}

	fn rustfmt(input: String, config: &RustfmtConfig) -> Result<String> {
	pipe_string_through_process(
	input,
	"rustfmt",
	&config.exe_path,
	config.cmdline_args.iter().map(OsString::as_os_str),
	)
	}

	fn clang_format(input: String, clang_format_exe_path: &Path) -> Result<String> {
	pipe_string_through_process(
	input,
	"clang-format",
	clang_format_exe_path,
	[OsStr::new("--style=google")],
	)
	}

	#[cfg(test)]
	mod tests {
	use super::*;

	use super::Result;
	use quote::quote;
	use tempfile::tempdir;

	#[test]
	fn test_simple_token_stream() -> Result<()> {
	let token_stream = quote! {
	struct Foo {}

	impl Bar for Foo {
	fn bar(&self) {}
	}
	};
	assert_eq!(
	tokens_to_string(token_stream)?,
	"struct Foo{ }impl Bar for Foo{ fn bar(&self){ } }"
	);
	Ok(())
	}

	#[test]
	fn test_space_idents_and_literals() -> Result<()> {
	let token_stream = quote! { foo 42 bar 23 };
	assert_eq!(tokens_to_string(token_stream)?, "foo 42 bar 23");
	Ok(())
	}

	#[test]
	fn test_dont_space_punctuation() -> Result<()> {
	let token_stream = quote! { foo+42+bar+23 };
	assert_eq!(tokens_to_string(token_stream)?, "foo+42+bar+23");
	Ok(())
	}

	/// `foo : ::bar` is valid syntax, but `foo:::bar` is not.
	#[test]
	fn test_paamayim_nekudotayim() -> Result<()> {
	assert_eq!(tokens_to_string(quote! { x : :: y })?, "x: ::y");
	// The following variants are not syntactically valid, but good to have working
	// anyway.
	assert_eq!(tokens_to_string(quote! { x : : y })?, "x: : y");
	assert_eq!(tokens_to_string(quote! { x :: :: y })?, "x:: ::y");
	assert_eq!(tokens_to_string(quote! { x :: : y })?, "x:: : y");
	Ok(())
	}

	#[test]
	fn test_newline_token() -> Result<()> {
	let token_stream = quote! { a __NEWLINE__ b };
	assert_eq!(tokens_to_string(token_stream)?, "a\nb");
	Ok(())
	}

	#[test]
	fn test_space_token() -> Result<()> {
	let token_stream = quote! { a __SPACE__ = __SPACE__ b };
	assert_eq!(tokens_to_string(token_stream)?, "a = b");
	Ok(())
	}

	#[test]
	fn test_redundant_space_token() -> Result<()> {
	let token_stream = quote! { a __SPACE__ b };
	assert_eq!(tokens_to_string(token_stream)?, "a b");
	Ok(())
	}

	#[test]
	fn test_hash_token() -> Result<()> {
	let token_stream = quote! { a __HASH_TOKEN__ b };
	assert_eq!(tokens_to_string(token_stream)?, "a #b");
	Ok(())
	}

	#[test]
	fn test_include_standard_header() -> Result<()> {
	let token_stream = quote! { __HASH_TOKEN__ include <cstddef> };
	assert_eq!(tokens_to_string(token_stream)?, "#include<cstddef>");
	Ok(())
	}

	#[test]
	fn test_comments() -> Result<()> {
	let token_stream = quote! { __COMMENT__ "line1\nline2" };
	assert_eq!(tokens_to_string(token_stream)?, "// line1\n// line2\n");
	Ok(())
	}

	#[test]
	fn test_invalid_comment() -> Result<()> {
	assert!(tokens_to_string(quote! { __COMMENT__ }).is_err());
	assert!(tokens_to_string(quote! { __COMMENT__ ident }).is_err());
	Ok(())
	}

	#[test]
	fn test_doc_comment() -> Result<()> {
	// token_stream_printer (and rustfmt) don't put a space between /// and the doc
	// comment, if the space is desired, it has to appear in the annotation.
	assert_eq!(
	rs_tokens_to_formatted_string_for_tests(quote! { #[doc = "hello"] struct X {} })?,
	"///hello\nstruct X {}\n"
	);
	assert_eq!(
	rs_tokens_to_formatted_string_for_tests(
	quote! { #[doc = "hello\nworld"] struct X {} }
	)?,
	"///hello\n///world\nstruct X {}\n"
	);
	Ok(())
	}

	#[test]
	fn test_doc_comment_leading_spaces() -> Result<()> {
	assert_eq!(
	rs_tokens_to_formatted_string_for_tests(quote! { #[doc = " hello"] struct X {} })?,
	"/// hello\nstruct X {}\n"
	);
	assert_eq!(
	rs_tokens_to_formatted_string_for_tests(
	quote! { #[doc = " hello\n world"] struct X {} }
	)?,
	"/// hello\n/// world\nstruct X {}\n"
	);
	Ok(())
	}

	#[test]
	fn test_special_tokens_in_groups() -> Result<()> {
	assert_eq!(tokens_to_string(quote! {{ a __NEWLINE__ b }})?, "{ a\nb }");
	assert_eq!(tokens_to_string(quote! {{ a __SPACE__ b }})?, "{ a b }");
	assert_eq!(tokens_to_string(quote! {(a __COMMENT__ "b")})?, "(a // b\n)");
	assert_eq!(tokens_to_string(quote! {[__HASH_TOKEN__ a]})?, "[#a]");
	Ok(())
	}

	#[test]
	fn test_rs_tokens_to_formatted_string_for_tests() {
	let input = quote! {
	fn foo() {}
	fn bar() {}
	};
	let output = rs_tokens_to_formatted_string_for_tests(input).unwrap();
	assert_eq!(
	output,
	r#"fn foo() {}
	fn bar() {}
	"#
	);
	}

	#[test]
	fn test_rs_tokens_to_formatted_string() {
	let cfg = RustfmtConfig::new(Path::new(RUSTFMT_EXE_PATH_FOR_TESTING), None);
	let input = quote! {
	fn bar() {}
	fn foo(x: i32, y: i32) -> i32 { x + y }
	};
	let output = rs_tokens_to_formatted_string(input, &cfg).unwrap();
	assert_eq!(
	output,
	r#"fn bar() {}
	fn foo(x: i32, y: i32) -> i32 {
	x + y
	}
	"#
	);
	}

	#[test]
	fn test_rs_tokens_to_formatted_string_with_custom_rustfmt_toml() -> Result<()> {
	let tmpdir = tempdir()?;
	let rustfmt_toml_path = tmpdir.path().join("rustfmt-for-tests.toml");
	std::fs::write(
	&rustfmt_toml_path,
	r#" edition = "2021"
	version = "Two"
	fn_args_layout="Vertical" "#,
	)?;
	let cfg =
	RustfmtConfig::new(Path::new(RUSTFMT_EXE_PATH_FOR_TESTING), Some(&rustfmt_toml_path));
	let input = quote! {
	fn bar() {}
	fn foo(x: i32, y: i32) -> i32 { x + y }
	};

	let output = rs_tokens_to_formatted_string(input, &cfg).unwrap();
	assert_eq!(
	output,
	r#"fn bar() {}
	fn foo(
	x: i32,
	y: i32,
	) -> i32 {
	x + y
	}
	"#
	);
	Ok(())
	}

	#[test]
	fn test_cc_tokens_to_formatted_string_for_tests() {
	let input = quote! {
	namespace ns {
	void foo() {}
	void bar() {}
	}
	};
	let output = cc_tokens_to_formatted_string_for_tests(input).unwrap();
	assert_eq!(
	output,
	r#"namespace ns {
	void foo() {}
	void bar() {}
	} // namespace ns"#
	);
	}
	}