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/*[toml]
[dependencies]
# Alternatively can use `use proc_macro2;` with dependency inference and default config
proc-macro2 = { version = "1", features = ["span-locations"] }
*/
/// Published example from the `syn` crate. Description "Parse a Rust source file
/// into a `syn::File` and print out a debug representation of the syntax tree."
///
/// Pass it the absolute or relative path of any Rust PROGRAM source file, e.g. its own
/// path that you passed to the script runner to invoke it.
///
/// NB: Pick a script that is a valid program (containing `fn main()` as opposed to a snippet).
//# Purpose: show off the power of `syn`.
//# Categories: AST, crates, technique
//# Sample arguments: `-- demo/hello_main.rs`
// Parse a Rust source file into a `syn::File` and print out a debug
// representation of the syntax tree.
//
// Use the following command from this directory to test this program by
// running it on its own source code:
//
// cargo run -- src/main.rs
//
// The output will begin with:
//
// File {
// shebang: None,
// attrs: [
// Attribute {
// pound_token: Pound,
// style: AttrStyle::Inner(
// ...
// }
use colored::Colorize;
use std::borrow::Cow;
use std::env;
use std::ffi::OsStr;
use std::fmt::{self, Display};
use std::fs;
use std::io::{self, Write};
use std::path::{Path, PathBuf};
use std::process;
enum Error {
IncorrectUsage,
ReadFile(io::Error),
ParseFile {
error: syn::Error,
filepath: PathBuf,
source_code: String,
},
}
impl Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
Error::IncorrectUsage => write!(f, "Usage: syn_dump_syntax path/to/filename.rs"),
Error::ReadFile(error) => write!(f, "Unable to read file: {}", error),
Error::ParseFile {
error,
filepath,
source_code,
} => render_location(f, error, filepath, source_code),
}
}
}
fn main() {
if let Err(error) = try_main() {
let _ = writeln!(io::stderr(), "{}", error);
process::exit(1);
}
}
fn try_main() -> Result<(), Error> {
let mut args = env::args_os();
let _ = args.next(); // executable name
let filepath = match (args.next(), args.next()) {
(Some(arg), None) => PathBuf::from(arg),
_ => return Err(Error::IncorrectUsage),
};
let code = fs::read_to_string(&filepath).map_err(Error::ReadFile)?;
let syntax = syn::parse_file(&code).map_err({
|error| Error::ParseFile {
error,
filepath,
source_code: code,
}
})?;
println!("{:#?}", syntax);
Ok(())
}
// Render a rustc-style error message, including colors.
//
// error: Syn unable to parse file
// --> main.rs:40:17
// |
// 40 | fn fmt(&self formatter: &mut fmt::Formatter) -> fmt::Result {
// | ^^^^^^^^^ expected `,`
//
fn render_location(
formatter: &mut fmt::Formatter,
err: &syn::Error,
filepath: &Path,
code: &str,
) -> fmt::Result {
let start = err.span().start();
let mut end = err.span().end();
let code_line = match start.line.checked_sub(1).and_then(|n| code.lines().nth(n)) {
Some(line) => line,
None => return render_fallback(formatter, err),
};
if end.line > start.line {
end.line = start.line;
end.column = code_line.len();
}
let filename = filepath
.file_name()
.map(OsStr::to_string_lossy)
.unwrap_or(Cow::Borrowed("main.rs"));
write!(
formatter,
"\n\
{error}{header}\n\
{indent}{arrow} {filename}:{linenum}:{colnum}\n\
{indent} {pipe}\n\
{label} {pipe} {code}\n\
{indent} {pipe} {offset}{underline} {message}\n\
",
error = "error".red().bold(),
header = ": Syn unable to parse file".bold(),
indent = " ".repeat(start.line.to_string().len()),
arrow = "-->".blue().bold(),
filename = filename,
linenum = start.line,
colnum = start.column,
pipe = "|".blue().bold(),
label = start.line.to_string().blue().bold(),
code = code_line.trim_end(),
offset = " ".repeat(start.column),
underline = "^"
.repeat(end.column.saturating_sub(start.column).max(1))
.red()
.bold(),
message = err.to_string().red(),
)
}
fn render_fallback(formatter: &mut fmt::Formatter, err: &syn::Error) -> fmt::Result {
write!(formatter, "Unable to parse file: {}", err)
}