feat(ast_tools): better handling of formatting errors (#10025)

Improve handling of parsing/formatting errors in outputs.

Previously would panic or output an empty file, which made debugging what was causing the problem difficult. Instead output the unformatted source, so can look at it and figure out what's wrong.

tasks/ast_tools/src/output/javascript.rs

@@ -3,6 +3,8 @@ use std::{
     process::{Command, Stdio},
 };
 
+use crate::log;
+
 use super::add_header;
 
 /// Format Javascript/Typescript code, and add header.
@@ -16,7 +18,8 @@ fn format(source_text: &str) -> String {
     let mut dprint = Command::new("dprint")
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
-        .args(["fmt", "--stdin", "dummy.ts"])
+        .stderr(Stdio::piped())
+        .args(["fmt", "--stdin", "placeholder_filename.ts"])
         .spawn()
         .expect("Failed to run dprint (is it installed?)");
 
@@ -25,5 +28,13 @@ fn format(source_text: &str) -> String {
     stdin.flush().unwrap();
 
     let output = dprint.wait_with_output().unwrap();
-    String::from_utf8(output.stdout).unwrap()
+    if output.status.success() {
+        String::from_utf8(output.stdout).unwrap()
+    } else {
+        // Formatting failed. Return unformatted code, to aid debugging.
+        let error =
+            String::from_utf8(output.stderr).unwrap_or_else(|_| "Unknown error".to_string());
+        log!("FAILED TO FORMAT JS/TS code:\n{error}");
+        source_text.to_string()
+    }
 }

tasks/ast_tools/src/output/mod.rs

@@ -47,7 +47,7 @@ impl Output {
 
         let (path, code) = match self {
             Self::Rust { path, tokens } => {
-                let code = print_rust(tokens, &generator_path);
+                let code = print_rust(&tokens, &generator_path);
                 (path, code)
             }
             Self::RustString { path, code } => {

tasks/ast_tools/src/output/rust.rs

@@ -7,11 +7,23 @@ use lazy_regex::{Captures, Lazy, Regex, lazy_regex, regex::Replacer};
 use proc_macro2::TokenStream;
 use syn::parse2;
 
+use crate::log;
+
 use super::add_header;
 
 /// Format Rust code, and add header.
-pub fn print_rust(tokens: TokenStream, generator_path: &str) -> String {
-    let code = prettyplease::unparse(&parse2(tokens).unwrap());
+pub fn print_rust(tokens: &TokenStream, generator_path: &str) -> String {
+    // Note: Cloning `TokenStream` is cheap, because internally it's an `Rc`
+    let file = match parse2(tokens.clone()) {
+        Ok(file) => file,
+        Err(err) => {
+            // Parsing failed. Return unformatted code, to aid debugging.
+            log!("FAILED TO PARSE Rust code:\n{err}");
+            return tokens.to_string();
+        }
+    };
+
+    let code = prettyplease::unparse(&file);
     let code = COMMENT_REGEX.replace_all(&code, CommentReplacer).to_string();
     let code = add_header(&code, generator_path, "//");
     rust_fmt(&code)
@@ -24,6 +36,7 @@ pub fn rust_fmt(source_text: &str) -> String {
     let mut rustfmt = Command::new("rustfmt")
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
         .spawn()
         .expect("Failed to run rustfmt (is it installed?)");
 
@@ -32,7 +45,15 @@ pub fn rust_fmt(source_text: &str) -> String {
     stdin.flush().unwrap();
 
     let output = rustfmt.wait_with_output().unwrap();
-    String::from_utf8(output.stdout).unwrap()
+    if output.status.success() {
+        String::from_utf8(output.stdout).unwrap()
+    } else {
+        // Formatting failed. Return unformatted code, to aid debugging.
+        let error =
+            String::from_utf8(output.stderr).unwrap_or_else(|_| "Unknown error".to_string());
+        log!("FAILED TO FORMAT Rust code:\n{error}");
+        source_text.to_string()
+    }
 }
 
 /// Replace doc comments which start with `@` with plain comments or line breaks.