feat: Allow prqlc to print backtraces on errors

prql-compiler/prqlc/src/cli.rs

@@ -5,11 +5,13 @@ use ariadne::Source;
 use clap::{CommandFactory, Parser, Subcommand, ValueHint};
 use clio::Output;
 use itertools::Itertools;
+use std::backtrace;
+use std::fs::File;
 use std::io::Write;
+use std::ops::Range;
 use std::path::PathBuf;
 use std::process::exit;
 use std::str::FromStr;
-use std::{fs::File, ops::Range};
 
 use prql_compiler::semantic::{self, reporting::*};
 use prql_compiler::{ast::pl::Lineage, pl_to_prql};
@@ -27,6 +29,17 @@ pub fn main() -> color_eyre::eyre::Result<()> {
 
     if let Err(error) = cli.command.run() {
         eprintln!("{error}");
+        // TODO: this is clunky — we're using `backtrace.status()` to check if
+        // backtraces are enabled, but then printing the backtrace from the
+        // error. Is there a way to check whether backtrades are enabled without
+        // capturing another one; e.g. from the error itself?
+        //
+        // Without this, we get a `<disabled>` message most of the time, which
+        // is kinda confusing.
+        if let backtrace::BacktraceStatus::Captured = backtrace::Backtrace::capture().status() {
+            eprintln!("{:#}", error.backtrace());
+        }
+
         exit(1)
     }
 

prql-compiler/prqlc/tests/test.rs

@@ -186,10 +186,12 @@ fn project_path() -> PathBuf {
 
 fn prqlc_command() -> Command {
     let mut cmd = Command::new(get_cargo_bin("prqlc"));
-    // We set this in CI to force color output, but we don't want `prqlc` to
+    // We set `CLICOLOR_FORCE` in CI to force color output, but we don't want `prqlc` to
     // output color for our snapshot tests. And it seems to override the
     // `--color=never` flag.
     cmd.env_remove("CLICOLOR_FORCE");
+    // We don't want the tests to be affected by the user's `RUST_BACKTRACE` setting.
+    cmd.env_remove("RUST_BACKTRACE");
     cmd.args(["--color=never"]);
     cmd
 }