clif-util: add the souper-to-peepmatic subcommand (#2200)

This adds a subcommand to the `clif-util` CLI for exposing the Souper->Peepmatic
translation machinery that was introduced in #2192.

cranelift/src/souper_to_peepmatic.rs

@@ -0,0 +1,32 @@
+use std::io::{Read, Write};
+use std::path::Path;
+
+pub fn run(input: &Path, output: &Path) -> Result<(), String> {
+    let peepmatic_dsl = if input == Path::new("-") {
+        let stdin = std::io::stdin();
+        let mut stdin = stdin.lock();
+        let mut souper_dsl = vec![];
+        stdin
+            .read_to_end(&mut souper_dsl)
+            .map_err(|e| format!("failed to read from stdin: {}", e))?;
+        let souper_dsl =
+            String::from_utf8(souper_dsl).map_err(|e| format!("stdin is not UTF-8: {}", e))?;
+        peepmatic_souper::convert_str(&souper_dsl, Some(Path::new("stdin")))
+            .map_err(|e| e.to_string())?
+    } else {
+        peepmatic_souper::convert_file(input).map_err(|e| e.to_string())?
+    };
+
+    if output == Path::new("-") {
+        let stdout = std::io::stdout();
+        let mut stdout = stdout.lock();
+        stdout
+            .write_all(peepmatic_dsl.as_bytes())
+            .map_err(|e| format!("error writing to stdout: {}", e))?;
+    } else {
+        std::fs::write(output, peepmatic_dsl.as_bytes())
+            .map_err(|e| format!("error writing to {}: {}", output.display(), e))?;
+    }
+
+    Ok(())
+}