Try to invoke lalrpop from parser build script

Author: coolreader18

parser/build.rs

@@ -1,26 +1,31 @@
 use std::fmt::Write as _;
 use std::fs::File;
-use std::io::{BufRead, BufReader, BufWriter, Write};
+use std::io::{self, BufRead, BufReader, BufWriter, Write};
 use std::path::PathBuf;
+use std::process::{self, Command};
 use tiny_keccak::{Hasher, Sha3};
 
 fn main() {
-    check_lalrpop();
+    check_lalrpop("src/python.lalrpop", "src/python.rs");
     gen_phf();
 }
 
-fn check_lalrpop() {
-    println!("cargo:rerun-if-changed=src/python.lalrpop");
-    let sha3_line = BufReader::with_capacity(128, File::open("src/python.rs").unwrap())
+fn check_lalrpop(source: &str, generated: &str) {
+    println!("cargo:rerun-if-changed={source}");
+
+    let sha_prefix = "// sha3: ";
+    let sha3_line = BufReader::with_capacity(128, File::open(generated).unwrap())
         .lines()
-        .nth(1)
-        .unwrap()
-        .unwrap();
-    let expected_sha3_str = sha3_line.strip_prefix("// sha3: ").unwrap();
+        .find_map(|line| {
+            let line = line.unwrap();
+            line.starts_with(sha_prefix).then(|| line)
+        })
+        .expect("no sha3 line?");
+    let expected_sha3_str = sha3_line.strip_prefix(sha_prefix).unwrap();
 
     let actual_sha3 = {
         let mut hasher = Sha3::v256();
-        let mut f = BufReader::new(File::open("src/python.lalrpop").unwrap());
+        let mut f = BufReader::new(File::open(source).unwrap());
         let mut line = String::new();
         while f.read_line(&mut line).unwrap() != 0 {
             if line.ends_with('\n') {
@@ -38,24 +43,40 @@ fn check_lalrpop() {
         hash
     };
 
+    if sha_equal(expected_sha3_str, &actual_sha3) {
+        return;
+    }
+    match Command::new("lalrpop").arg(source).status() {
+        Ok(stat) if stat.success() => {}
+        Ok(stat) => {
+            eprintln!("failed to execute lalrpop; exited with {stat}");
+            process::exit(stat.code().unwrap_or(1));
+        }
+        Err(e) if e.kind() == io::ErrorKind::NotFound => {
+            eprintln!(
+                "the lalrpop executable is not installed and parser/{source} has been changed"
+            );
+            eprintln!("please install lalrpop with `cargo install lalrpop`");
+            process::exit(1);
+        }
+        Err(e) => panic!("io error {e:#}"),
+    }
+}
+
+fn sha_equal(expected_sha3_str: &str, actual_sha3: &[u8; 32]) -> bool {
     // stupid stupid stupid hack. lalrpop outputs each byte as "{:x}" instead of "{:02x}"
-    let sha3_equal = if expected_sha3_str.len() == 64 {
+    if expected_sha3_str.len() == 64 {
         let mut expected_sha3 = [0u8; 32];
         for (i, b) in expected_sha3.iter_mut().enumerate() {
             *b = u8::from_str_radix(&expected_sha3_str[i * 2..][..2], 16).unwrap();
         }
-        actual_sha3 == expected_sha3
+        *actual_sha3 == expected_sha3
     } else {
         let mut actual_sha3_str = String::new();
         for byte in actual_sha3 {
             write!(actual_sha3_str, "{byte:x}").unwrap();
         }
         actual_sha3_str == expected_sha3_str
-    };
-
-    if !sha3_equal {
-        eprintln!("you need to recompile lalrpop!");
-        std::process::exit(1);
     }
 }