3 files changed, 194 insertions, 0 deletions
diff --git a/syn/examples/dump-syntax/Cargo.toml b/syn/examples/dump-syntax/Cargo.toml
new file mode 100644
index 0000000..0bc9f62
--- /dev/null
+++ b/syn/examples/dump-syntax/Cargo.toml
@@ -0,0 +1,17 @@
+[package]
+name = "dump-syntax"
+version = "0.0.0"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+edition = "2018"
+publish = false
+
+[dependencies]
+colored = "1.7"
+proc-macro2 = { version = "1.0", features = ["span-locations"] }
+
+[dependencies.syn]
+path = "../.."
+default-features = false
+features = ["parsing", "full", "extra-traits"]
+
+[workspace]
diff --git a/syn/examples/dump-syntax/README.md b/syn/examples/dump-syntax/README.md
new file mode 100644
index 0000000..37c84d8
--- /dev/null
+++ b/syn/examples/dump-syntax/README.md
@@ -0,0 +1,28 @@
+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: Inner(
+                Bang
+            ),
+            bracket_token: Bracket,
+            path: Path {
+                leading_colon: None,
+                segments: [
+    ...
+}
+```
diff --git a/syn/examples/dump-syntax/src/main.rs b/syn/examples/dump-syntax/src/main.rs
new file mode 100644
index 0000000..240b7a2
--- /dev/null
+++ b/syn/examples/dump-syntax/src/main.rs
@@ -0,0 +1,149 @@
+//! 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: Inner(
+//!         ...
+//!     }
+
+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;
+
+use colored::Colorize;
+
+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 {
+        use self::Error::*;
+
+        match self {
+            IncorrectUsage => write!(f, "Usage: dump-syntax path/to/filename.rs"),
+            ReadFile(error) => write!(f, "Unable to read file: {}", 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();
+
+    if start.line == end.line && start.column == end.column {
+        return render_fallback(formatter, err);
+    }
+
+    let code_line = match code.lines().nth(start.line - 1) {
+        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 - start.column).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)
+}