Generate pest file manually in the hopes to reduce spurious recompilations

3 files changed, 21 insertions, 7 deletions

diff --git a/dhall_parser/Cargo.toml b/dhall_parser/Cargo.toml
index a73d445..758c273 100644
--- a/dhall_parser/Cargo.toml
+++ b/dhall_parser/Cargo.toml
@@ -11,7 +11,8 @@ doctest = false
 
 [build-dependencies]
 abnf_to_pest = { path = "../abnf_to_pest" }
+pest_generator = "2.1"
+quote = "0.6.11"
 
 [dependencies]
 pest = { git = "https://github.com/pest-parser/pest" }
-pest_derive = "2.1"
diff --git a/dhall_parser/build.rs b/dhall_parser/build.rs
index a206517..bc342c1 100644
--- a/dhall_parser/build.rs
+++ b/dhall_parser/build.rs
@@ -1,6 +1,8 @@
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::{BufRead, BufReader, Read, Write};
+use std::env;
+use std::path::Path;
 
 use abnf_to_pest::{abnf_to_pest, PestRuleSettings};
 
@@ -68,5 +70,21 @@ fn main() -> std::io::Result<()> {
         "final_expression = {{ SOI ~ complete_expression ~ EOI }}"
     )?;
 
+
+    // Generate pest parser manually to avoid spurious recompilations
+    let derived = {
+        let pest_path = "dhall.pest";
+        let pest = quote::quote! {
+            #[grammar = #pest_path]
+            pub struct DhallParser;
+        };
+        pest_generator::derive_parser(pest, false)
+    };
+
+    let out_dir = env::var("OUT_DIR").unwrap();
+    let grammar_path = Path::new(&out_dir).join("grammar.rs");
+    let mut file = File::create(grammar_path)?;
+    writeln!(file, "pub struct DhallParser;\n{}", derived,)?;
+
     Ok(())
 }
diff --git a/dhall_parser/src/lib.rs b/dhall_parser/src/lib.rs
index 452b4cd..94b49b5 100644
--- a/dhall_parser/src/lib.rs
+++ b/dhall_parser/src/lib.rs
@@ -1,6 +1 @@
-#[allow(unused_imports)]
-use pest_derive::*;
-
-#[derive(Parser)]
-#[grammar = "dhall.pest"]
-pub struct DhallParser;
+include!(concat!(env!("OUT_DIR"), "/grammar.rs"));