cranelift-isle: Rewrite error reporting (#5318)

There were several issues with ISLE's existing error reporting
implementation.

- When using Miette for more readable error reports, it would panic if
  errors were reported from multiple files in the same run.
- Miette is pretty heavy-weight for what we're doing, with a lot of
  dependencies.
- The `Error::Errors` enum variant led to normalization steps in many
  places, to avoid using that variant to represent a single error.

This commit:
- replaces Miette with codespan-reporting
- gets rid of a bunch of cargo-vet exemptions
- replaces the `Error::Errors` variant with a new `Errors` type
- removes source info from `Error` variants so they're easy to construct
- adds source info only when formatting `Errors`
- formats `Errors` with a custom `Debug` impl
- shares common code between ISLE's callers, islec and cranelift-codegen
- includes a source snippet even with fancy-errors disabled

I tried to make this a series of smaller commits but I couldn't find any
good split points; everything was too entangled with everything else.

cranelift/isle/islec/Cargo.toml

@@ -7,7 +7,6 @@ license = "Apache-2.0 WITH LLVM-exception"
 publish = false
 
 [dependencies]
-cranelift-isle = { version = "*", path = "../isle/", features = ["miette-errors", "logging"] }
+cranelift-isle = { version = "*", path = "../isle/", features = ["fancy-errors", "logging"] }
 env_logger = { workspace = true }
-miette = { version = "5.1.0", features = ["fancy"] }
 clap = { workspace = true }

cranelift/isle/islec/src/main.rs

@@ -1,6 +1,6 @@
 use clap::Parser;
-use cranelift_isle::{compile, lexer, parser};
-use miette::{Context, IntoDiagnostic, Result};
+use cranelift_isle::compile;
+use cranelift_isle::error::Errors;
 use std::{
     default::Default,
     fs,
@@ -20,33 +20,19 @@ struct Opts {
     inputs: Vec<PathBuf>,
 }
 
-fn main() -> Result<()> {
+fn main() -> Result<(), Errors> {
     let _ = env_logger::try_init();
 
-    let _ = miette::set_hook(Box::new(|_| {
-        Box::new(
-            miette::MietteHandlerOpts::new()
-                // `miette` mistakenly uses braille-optimized output for emacs's
-                // `M-x shell`.
-                .force_graphical(true)
-                .build(),
-        )
-    }));
-
     let opts = Opts::parse();
-
-    let lexer = lexer::Lexer::from_files(opts.inputs)?;
-    let defs = parser::parse(lexer)?;
-    let code = compile::compile(&defs, &Default::default())?;
+    let code = compile::from_files(opts.inputs, &Default::default())?;
 
     let stdout = io::stdout();
     let (mut output, output_name): (Box<dyn Write>, _) = match &opts.output {
         Some(f) => {
-            let output = Box::new(
-                fs::File::create(f)
-                    .into_diagnostic()
-                    .with_context(|| format!("failed to create '{}'", f.display()))?,
-            );
+            let output =
+                Box::new(fs::File::create(f).map_err(|e| {
+                    Errors::from_io(e, format!("failed to create '{}'", f.display()))
+                })?);
             (output, f.display().to_string())
         }
         None => {
@@ -57,8 +43,7 @@ fn main() -> Result<()> {
 
     output
         .write_all(code.as_bytes())
-        .into_diagnostic()
-        .with_context(|| format!("failed to write to '{}'", output_name))?;
+        .map_err(|e| Errors::from_io(e, format!("failed to write to '{}'", output_name)))?;
 
     Ok(())
 }