Use diff tool to visualize desugaring changes

Cargo.lock

@@ -120,6 +120,15 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7a81dae078cea95a014a339291cec439d2f232ebe854a9d672b796c6afafa9b7"
 
+[[package]]
+name = "fastrand"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7a407cfaa3385c4ae6b23e84623d48c2798d06e3e6a1878f7f59f17b3f86499"
+dependencies = [
+ "instant",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.2.8"
@@ -146,6 +155,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "instant"
+version = "0.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a5bbe824c507c5da5956355e86a746d82e0e1464f65d862cc5e71da70e94b2c"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "libc"
 version = "0.2.137"
@@ -233,6 +251,24 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "redox_syscall"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fb5a58c1855b4b6819d59012155603f0b22ad30cad752600aadfcb695265519a"
+dependencies = [
+ "bitflags",
+]
+
+[[package]]
+name = "remove_dir_all"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3acd125665422973a33ac9d3dd2df85edad0f4ae9b00dafb1a05e43a9f5ef8e7"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "strsim"
 version = "0.10.0"
@@ -258,6 +294,21 @@ dependencies = [
  "chumsky",
  "clap",
  "pretty",
+ "tempfile",
+]
+
+[[package]]
+name = "tempfile"
+version = "3.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5cdb1ef4eaeeaddc8fbd371e5017057064af0911902ef36b39801f67cc6d79e4"
+dependencies = [
+ "cfg-if",
+ "fastrand",
+ "libc",
+ "redox_syscall",
+ "remove_dir_all",
+ "winapi",
 ]
 
 [[package]]

Cargo.toml

@@ -8,3 +8,4 @@ anyhow = "1.0.66"
 chumsky = "0.8.0"
 clap = { version = "4.0.26", features = ["derive", "deprecated"] }
 pretty = "0.11.3"
+tempfile = "3.3.0"

src/main.rs

@@ -14,8 +14,9 @@
 // Clippy lints
 #![warn(clippy::use_self)]
 
-use std::fs;
+use std::io::Write;
 use std::path::PathBuf;
+use std::{fs, process};
 
 use anyhow::anyhow;
 use chumsky::Parser as _;
@@ -32,9 +33,19 @@ mod value;
 
 #[derive(Parser)]
 enum Command {
-    Parse { file: PathBuf },
+    Parse {
-    Pretty { file: PathBuf },
+        file: PathBuf,
-    Desugar { file: PathBuf },
+    },
+    Pretty {
+        file: PathBuf,
+    },
+    Desugar {
+        file: PathBuf,
+        #[arg(long, short, default_value = "diff")]
+        difftool: String,
+        #[arg(long, short = 'a')]
+        diffarg: Vec<String>,
+    },
 }
 
 #[derive(Parser)]
@@ -72,14 +83,23 @@ fn main() -> anyhow::Result<()> {
             println!("{}", pretty::pretty_to_string(program, 100));
         }
 
-        Command::Desugar { file } => {
+        Command::Desugar {
+            file,
+            difftool,
+            diffarg,
+        } => {
             let content = fs::read_to_string(&file)?;
             let stream = span::stream_from_str(&content);
             let mut program = parser::parser()
                 .parse(stream)
                 .map_err(|e| anyhow!("{e:?}"))?;
 
-            println!("{}", pretty::pretty_to_string(program.clone(), 100));
+            let mut builder = tempfile::Builder::new();
+            builder.suffix(".tada");
+
+            let mut prev = builder.tempfile()?;
+            prev.write_all(pretty::pretty_to_string(program.clone(), 100).as_bytes())?;
+            prev.flush()?;
 
             loop {
                 let (new_program, desugared) = program.desugar();
@@ -88,10 +108,18 @@ fn main() -> anyhow::Result<()> {
                     break;
                 }
 
-                println!();
+                let mut cur = builder.tempfile()?;
-                println!("================================================================================");
+                cur.write_all(pretty::pretty_to_string(program.clone(), 100).as_bytes())?;
-                println!();
+                cur.flush()?;
-                println!("{}", pretty::pretty_to_string(program.clone(), 100));
+
+                process::Command::new(&difftool)
+                    .args(&diffarg)
+                    .arg(prev.path())
+                    .arg(cur.path())
+                    .spawn()?
+                    .wait()?;
+
+                prev = cur;
             }
         }
     }