Fold Error source chain Display output into shader errors

cli/src/bin/naga.rs

@@ -1,7 +1,13 @@
 #![allow(clippy::manual_strip)]
 #[allow(unused_imports)]
 use std::fs;
-use std::{error::Error, fmt, io::Read, path::Path, str::FromStr};
+use std::{
+    error::Error,
+    fmt,
+    io::{stderr, Read, Write},
+    path::Path,
+    str::FromStr,
+};
 
 /// Translate shaders to different formats.
 #[derive(argh::FromArgs, Debug, Clone)]
@@ -161,18 +167,18 @@ trait PrettyResult {
     fn unwrap_pretty(self) -> Self::Target;
 }
 
-fn print_err(error: &dyn Error) {
-    eprint!("{error}");
+fn print_err(out: &mut dyn Write, error: &dyn Error) {
+    write!(out, "{error}").unwrap();
 
     let mut e = error.source();
     if e.is_some() {
-        eprintln!(": ");
+        writeln!(out, ":").unwrap();
     } else {
-        eprintln!();
+        writeln!(out).unwrap();
     }
 
     while let Some(source) = e {
-        eprintln!("\t{source}");
+        writeln!(out, "        {source}").unwrap();
         e = source.source();
     }
 }
@@ -183,7 +189,7 @@ impl<T, E: Error> PrettyResult for Result<T, E> {
         match self {
             Result::Ok(value) => value,
             Result::Err(error) => {
-                print_err(&error);
+                print_err(&mut stderr().lock(), &error);
                 std::process::exit(1);
             }
         }
@@ -192,7 +198,7 @@ impl<T, E: Error> PrettyResult for Result<T, E> {
 
 fn main() {
     if let Err(e) = run() {
-        print_err(e.as_ref());
+        print_err(&mut stderr().lock(), e.as_ref());
         std::process::exit(1);
     }
 }
@@ -339,8 +345,9 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
             if let Some(input) = input_text {
                 let filename = input_path.file_name().and_then(std::ffi::OsStr::to_str);
                 emit_annotated_error(&error, filename.unwrap_or("input"), &input);
+            } else {
+                print_err(&mut stderr().lock(), &error);
             }
-            print_err(&error);
             None
         }
     };
@@ -362,8 +369,6 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
             .ok_or(CliError("Output filename not valid unicode"))?
         {
             "txt" => {
-                use std::io::Write;
-
                 let mut file = fs::File::create(output_path)?;
                 writeln!(file, "{module:#?}")?;
                 if let Some(ref info) = info {
@@ -553,7 +558,14 @@ pub fn emit_annotated_error<E: Error>(ann_err: &WithSpan<E>, filename: &str, sou
     let config = codespan_reporting::term::Config::default();
     let writer = StandardStream::stderr(ColorChoice::Auto);
 
-    let diagnostic = Diagnostic::error().with_labels(
+    let mut msg_buf = Vec::new();
+    print_err(&mut msg_buf, ann_err);
+    let msg = String::from_utf8(msg_buf)
+        .unwrap()
+        // NOTE: `replace` is intended to correct the alignment of multi-line messages against the
+        // `error: ` prefix, which is 7 characters.
+        .replace('\n', "\n       ");
+    let diagnostic = Diagnostic::error().with_message(msg).with_labels(
         ann_err
             .spans()
             .map(|(span, desc)| {

src/valid/mod.rs

@@ -211,7 +211,7 @@ pub enum ValidationError {
         name: String,
         source: FunctionError,
     },
-    #[error("Entry point {name} at {stage:?} is invalid")]
+    #[error("Entry point '{name}' at {stage:?} is invalid")]
     EntryPoint {
         stage: crate::ShaderStage,
         name: String,