Silence annoying rustfmt config warnings

tools/ci/Cargo.toml

@@ -10,4 +10,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-xshell = "0.1"
+duct = "0.13"

tools/ci/src/main.rs

@@ -1,19 +1,47 @@
-use xshell::cmd;
+use std::io::BufRead;
+
+use duct::cmd;
 
 fn main() {
     // When run locally, results may from actual CI runs triggered by .github/workflows/ci.yml
     // - Official CI runs latest stable
     // - Local runs use whatever the default Rust is locally
 
     // See if any code needs to be formatted
-    cmd!("cargo fmt --all -- --check")
+    println!("$ cargo fmt --all -- --check");
+    let errput = cmd!("cargo", "fmt", "--all", "--", "--check")
+        .stderr_capture()
         .run()
         .expect("Please run 'cargo fmt --all' to format your code.");
+    // Capture stderr, filter out lines starting with "Warning:" that complain about nightly-only
+    // options in rustfmt.toml -- we can remove this (and maybe switch back to `xshell` instead of
+    // `duct`) once either rustfmt.toml doesn't cause warnings in stable or nightly rust, or rustfmt
+    // learns an option to silence warnings provoked by the config file.
+    errput
+        .stderr
+        .lines()
+        .filter_map(|l| l.ok())
+        .filter(|l| !l.starts_with("Warning"))
+        .for_each(|l| eprintln!("{}", l));
 
     // See if clippy has any complaints.
     // - Type complexity must be ignored because we use huge templates for queries
     // - `-A clippy::manual-strip` strip_prefix support was added in 1.45
-    cmd!("cargo clippy --workspace --all-targets --all-features -- -D warnings -A clippy::type_complexity -A clippy::manual-strip")
+    println!("$ cargo clippy --workspace --all-targets --all-features -- -D warnings -A clippy::type_complexity -A clippy::manual-strip");
+    cmd!(
+        "cargo",
+        "clippy",
+        "--workspace",
+        "--all-targets",
+        "--all-features",
+        "--",
+        "-D",
+        "warnings",
+        "-A",
+        "clippy::type_complexity",
+        "-A",
+        "clippy::manual-strip"
+    )
     .run()
     .expect("Please fix clippy errors in output above.");
 }