chore(lib): remove error branch from LUT if it is unreachable

logos-codegen/Cargo.toml

@@ -9,6 +9,7 @@ syn = { version = "2.0.13", features = ["full"] }
 
 [dev-dependencies]
 pretty_assertions = "1.4.0"
+rstest = "0.18.2"
 
 [features]
 # Enables debug messages

logos-codegen/src/generator/fork.rs

@@ -87,9 +87,18 @@ impl<'a> Generator<'a> {
             })
             .collect::<TokenStream>();
 
-        let jumps = &jumps;
+        let may_error = table.iter().any(|&idx| idx == 0);
+
+        let jumps = jumps.as_slice();
         let table = table.iter().copied().map(|idx| &jumps[idx as usize]);
 
+        let jumps = if may_error { jumps } else { &jumps[1..] };
+        let error_branch = if may_error {
+            Some(quote!(Jump::__ => #miss))
+        } else {
+            None
+        };
+
         quote! {
             enum Jump {
                 #(#jumps,)*
@@ -105,7 +114,7 @@ impl<'a> Generator<'a> {
 
             match LUT[#byte as usize] {
                 #branches
-                Jump::__ => #miss,
+                #error_branch
             }
         }
     }

logos-codegen/tests/codegen.rs

@@ -0,0 +1,31 @@
+use std::{error::Error, io, path::PathBuf};
+
+#[rstest::rstest]
+#[case("simple")]
+#[case("no_error_lut")]
+pub fn test_codegen(#[case] fixture: &str) -> Result<(), Box<dyn Error>> {
+    let mut fixture_dir = PathBuf::new();
+    fixture_dir.push(env!("CARGO_MANIFEST_DIR"));
+    fixture_dir.push("tests");
+    fixture_dir.push("data");
+    fixture_dir.push(fixture);
+
+    let input = fixture_dir.join("input.rs");
+    fixture_dir.push("output.rs");
+    let output_file = fixture_dir;
+
+    let input = std::fs::read_to_string(input)?;
+    let output = std::fs::read_to_string(&output_file)?;
+
+    let generated = logos_codegen::generate(input.parse()?);
+    let generated = generated.to_string();
+
+    if std::env::var("BLESS_CODEGEN").is_ok_and(|value| value == "1") {
+        std::fs::write(&output_file, &generated)?;
+        return Ok(());
+    }
+
+    assert_eq!(generated, output, "Codegen test failed: `{fixture}`, run tests again with env var `BLESS_CODEGEN=1` to bless these changes");
+
+    Ok(())
+}

logos-codegen/tests/data/no_error_lut/input.rs

@@ -0,0 +1,10 @@
+#[derive(Logos)]
+#[logos(source = [u8])]
+enum Token {
+    #[token("\n")]
+    Newline,
+    #[regex(".")]
+    AnyUnicode,
+    #[regex(b".", priority = 0)]
+    Any,
+}

logos-codegen/tests/data/no_error_lut/output.rs

@@ -0,0 +1 @@
+impl < 's > :: logos :: Logos < 's > for Token { type Error = () ; type Extras = () ; type Source = [u8] ; fn lex (lex : & mut :: logos :: Lexer < 's , Self >) { use :: logos :: internal :: { LexerInternal , CallbackResult } ; type Lexer < 's > = :: logos :: Lexer < 's , Token > ; fn _end < 's > (lex : & mut Lexer < 's >) { lex . end () } fn _error < 's > (lex : & mut Lexer < 's >) { lex . bump_unchecked (1) ; lex . error () ; } macro_rules ! _fast_loop { ($ lex : ident , $ test : ident , $ miss : expr) => { while let Some (arr) = $ lex . read :: < & [u8 ; 16] > () { if $ test (arr [0]) { if $ test (arr [1]) { if $ test (arr [2]) { if $ test (arr [3]) { if $ test (arr [4]) { if $ test (arr [5]) { if $ test (arr [6]) { if $ test (arr [7]) { if $ test (arr [8]) { if $ test (arr [9]) { if $ test (arr [10]) { if $ test (arr [11]) { if $ test (arr [12]) { if $ test (arr [13]) { if $ test (arr [14]) { if $ test (arr [15]) { $ lex . bump_unchecked (16) ; continue ; } $ lex . bump_unchecked (15) ; return $ miss ; } $ lex . bump_unchecked (14) ; return $ miss ; } $ lex . bump_unchecked (13) ; return $ miss ; } $ lex . bump_unchecked (12) ; return $ miss ; } $ lex . bump_unchecked (11) ; return $ miss ; } $ lex . bump_unchecked (10) ; return $ miss ; } $ lex . bump_unchecked (9) ; return $ miss ; } $ lex . bump_unchecked (8) ; return $ miss ; } $ lex . bump_unchecked (7) ; return $ miss ; } $ lex . bump_unchecked (6) ; return $ miss ; } $ lex . bump_unchecked (5) ; return $ miss ; } $ lex . bump_unchecked (4) ; return $ miss ; } $ lex . bump_unchecked (3) ; return $ miss ; } $ lex . bump_unchecked (2) ; return $ miss ; } $ lex . bump_unchecked (1) ; return $ miss ; } return $ miss ; } while $ lex . test ($ test) { $ lex . bump_unchecked (1) ; } $ miss } ; } # [inline] fn goto1_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: Newline)) ; } # [inline] fn goto11_ctx11_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: Any)) ; } # [inline] fn goto2_ctx11_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: AnyUnicode)) ; } # [inline] fn goto16_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 2usize] > () { Some ([128u8 ..= 159u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (2usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto17_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 3usize] > () { Some ([144u8 ..= 191u8 , 128u8 ..= 191u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (3usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto2_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: AnyUnicode)) ; } # [inline] fn goto13_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 1usize] > () { Some ([128u8 ..= 191u8]) => { lex . bump_unchecked (1usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto18_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 3usize] > () { Some ([128u8 ..= 191u8 , 128u8 ..= 191u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (3usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto15_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 2usize] > () { Some ([128u8 ..= 191u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (2usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto14_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 2usize] > () { Some ([160u8 ..= 191u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (2usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto19_ctx11_x < 's > (lex : & mut Lexer < 's >) { match lex . read :: < & [u8 ; 3usize] > () { Some ([128u8 ..= 143u8 , 128u8 ..= 191u8 , 128u8 ..= 191u8]) => { lex . bump_unchecked (3usize) ; goto2_ctx11_x (lex) } , _ => goto11_ctx11_x (lex) , } } # [inline] fn goto11_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: Any)) ; } # [inline] fn goto20 < 's > (lex : & mut Lexer < 's >) { enum Jump { J1 , J16 , J17 , J2 , J13 , J18 , J15 , J14 , J19 , J11 , } const LUT : [Jump ; 256] = { use Jump :: * ; [J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J1 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J2 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J13 , J14 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J15 , J16 , J15 , J15 , J17 , J18 , J18 , J18 , J19 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11 , J11] } ; let byte = match lex . read :: < u8 > () { Some (byte) => byte , None => return _end (lex) , } ; match LUT [byte as usize] { Jump :: J1 => { lex . bump_unchecked (1usize) ; goto1_x (lex) } , Jump :: J16 => { lex . bump_unchecked (1usize) ; goto16_ctx11_x (lex) } , Jump :: J17 => { lex . bump_unchecked (1usize) ; goto17_ctx11_x (lex) } , Jump :: J2 => { lex . bump_unchecked (1usize) ; goto2_x (lex) } , Jump :: J13 => { lex . bump_unchecked (1usize) ; goto13_ctx11_x (lex) } , Jump :: J18 => { lex . bump_unchecked (1usize) ; goto18_ctx11_x (lex) } , Jump :: J15 => { lex . bump_unchecked (1usize) ; goto15_ctx11_x (lex) } , Jump :: J14 => { lex . bump_unchecked (1usize) ; goto14_ctx11_x (lex) } , Jump :: J19 => { lex . bump_unchecked (1usize) ; goto19_ctx11_x (lex) } , Jump :: J11 => { lex . bump_unchecked (1usize) ; goto11_x (lex) } , } } goto20 (lex) } }

logos-codegen/tests/data/simple/input.rs

@@ -0,0 +1,5 @@
+#[derive(Logos, Debug, Clone, Copy, PartialEq)]
+enum Token {
+    #[regex("a-z")]
+    Letter,
+}

logos-codegen/tests/data/simple/output.rs

@@ -0,0 +1 @@
+impl < 's > :: logos :: Logos < 's > for Token { type Error = () ; type Extras = () ; type Source = str ; fn lex (lex : & mut :: logos :: Lexer < 's , Self >) { use :: logos :: internal :: { LexerInternal , CallbackResult } ; type Lexer < 's > = :: logos :: Lexer < 's , Token > ; fn _end < 's > (lex : & mut Lexer < 's >) { lex . end () } fn _error < 's > (lex : & mut Lexer < 's >) { lex . bump_unchecked (1) ; lex . error () ; } macro_rules ! _fast_loop { ($ lex : ident , $ test : ident , $ miss : expr) => { while let Some (arr) = $ lex . read :: < & [u8 ; 16] > () { if $ test (arr [0]) { if $ test (arr [1]) { if $ test (arr [2]) { if $ test (arr [3]) { if $ test (arr [4]) { if $ test (arr [5]) { if $ test (arr [6]) { if $ test (arr [7]) { if $ test (arr [8]) { if $ test (arr [9]) { if $ test (arr [10]) { if $ test (arr [11]) { if $ test (arr [12]) { if $ test (arr [13]) { if $ test (arr [14]) { if $ test (arr [15]) { $ lex . bump_unchecked (16) ; continue ; } $ lex . bump_unchecked (15) ; return $ miss ; } $ lex . bump_unchecked (14) ; return $ miss ; } $ lex . bump_unchecked (13) ; return $ miss ; } $ lex . bump_unchecked (12) ; return $ miss ; } $ lex . bump_unchecked (11) ; return $ miss ; } $ lex . bump_unchecked (10) ; return $ miss ; } $ lex . bump_unchecked (9) ; return $ miss ; } $ lex . bump_unchecked (8) ; return $ miss ; } $ lex . bump_unchecked (7) ; return $ miss ; } $ lex . bump_unchecked (6) ; return $ miss ; } $ lex . bump_unchecked (5) ; return $ miss ; } $ lex . bump_unchecked (4) ; return $ miss ; } $ lex . bump_unchecked (3) ; return $ miss ; } $ lex . bump_unchecked (2) ; return $ miss ; } $ lex . bump_unchecked (1) ; return $ miss ; } return $ miss ; } while $ lex . test ($ test) { $ lex . bump_unchecked (1) ; } $ miss } ; } # [inline] fn goto1_x < 's > (lex : & mut Lexer < 's >) { lex . set (Ok (Token :: Letter)) ; } # [inline] fn goto3_at1_with3 < 's > (lex : & mut Lexer < 's >) { match lex . read_at :: < & [u8 ; 2usize] > (1usize) { Some (b"-z") => { lex . bump_unchecked (3usize) ; goto1_x (lex) } , _ => _error (lex) , } } # [inline] fn goto4 < 's > (lex : & mut Lexer < 's >) { let arr = match lex . read :: < & [u8 ; 3usize] > () { Some (arr) => arr , None => return _end (lex) , } ; match arr [0] { b'a' => goto3_at1_with3 (lex) , _ => _error (lex) , } } goto4 (lex) } }