cera 0.5.5

Rust-native LLM inference engine
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136

//! Integration tests for GBNF grammar-constrained decoding, including validation of the
//! JSON grammar that ships with `cera-cli` (`--json`).

use std::sync::Arc;

use cera::grammar::{Grammar, GrammarMask, GrammarState};

/// The grammar bundled with `cera-cli --json`. Tested here so the shipped artifact can't
/// silently rot.
const JSON_GBNF: &str = include_str!("../../cera-cli/grammars/json.gbnf");

fn json() -> Arc<Grammar> {
    Arc::new(Grammar::parse(JSON_GBNF).expect("bundled json.gbnf must parse"))
}

/// Feed `input` byte-by-byte; returns the final state iff every byte was accepted.
fn run(g: &Arc<Grammar>, input: &[u8]) -> Option<GrammarState> {
    let mut st = GrammarState::new(g.clone());
    for &b in input {
        if !st.accepts(&[b]) {
            return None;
        }
        st.accept(&[b]);
    }
    Some(st)
}

fn accepts_complete(g: &Arc<Grammar>, s: &str) -> bool {
    run(g, s.as_bytes())
        .map(|st| st.is_complete())
        .unwrap_or(false)
}

#[test]
fn json_grammar_accepts_valid() {
    let g = json();
    for s in [
        "{}",
        "[]",
        r#"{"a":1}"#,
        "[1,2,3]",
        r#"{ "name" : "ada" , "age" : 36 }"#,
        r#"{"nested":{"a":[1,2,{"b":true}]},"x":null,"y":false}"#,
        "-12.5e+10",
        r#""a string with \"escapes\" and é and / and \\""#,
        "  \n  {\n  \"k\" : [ 1 , 2 ]\n}",
        "1234567890",
        "true",
    ] {
        assert!(accepts_complete(&g, s), "should accept valid JSON: {s:?}");
    }
}

#[test]
fn json_grammar_rejects_invalid() {
    let g = json();
    for s in [
        r#"{"k":}"#,  // missing value
        r#"{"k" 1}"#, // missing colon
        "[1,]",       // trailing comma
        "{,}",        // bogus
        r#"{key:1}"#, // unquoted key
        "[1,2,3",     // unterminated
        "01",         // leading zero
        r#""unterminated"#,
        "nul", // not a complete literal
    ] {
        assert!(
            !accepts_complete(&g, s),
            "should reject invalid JSON: {s:?}"
        );
    }
}

#[test]
fn json_incomplete_prefix_is_not_complete_but_extensible() {
    let g = json();
    // A partial object `{"a":` — parsed up to (and including) the colon, so the grammar
    // now expects a value. Accepted (the bytes parse) but not a complete value.
    let st = run(&g, b"{\"a\":").expect("prefix should parse");
    assert!(!st.is_complete());
    // ...and the next byte can begin any JSON value: a number, a string, or an array.
    assert!(st.accepts(b"1")); // number
    assert!(st.accepts(b"\"")); // string
    assert!(st.accepts(b"[")); // array
}

#[test]
fn mask_constrains_to_json_openers_then_advances() {
    let g = json();
    // Stub vocab: tokens that a JSON value can/can't start with.
    // 0="{", 1="[", 2="x" (invalid start), 3="\"", 4=EOS, 5=true.
    let token_bytes = vec![
        b"{".to_vec(),
        b"[".to_vec(),
        b"x".to_vec(),
        b"\"".to_vec(),
        Vec::new(),
        b"true".to_vec(),
    ];
    let special = vec![false, false, false, false, true, false];
    let mask = GrammarMask::new(token_bytes, Some(4), special);

    let mut st = GrammarState::new(g.clone());
    let mut logits = vec![0.0f32; 6];
    let allowed = mask.apply(&st, &mut logits);
    assert!(
        allowed >= 3,
        "‘{{’, ‘[’, ‘\"’, ‘true’ are all valid JSON openers"
    );
    assert_eq!(logits[0], 0.0, "'{{' allowed");
    assert_eq!(logits[1], 0.0, "'[' allowed");
    assert_eq!(
        logits[2],
        f32::NEG_INFINITY,
        "'x' is not a valid JSON start"
    );
    assert_eq!(logits[4], f32::NEG_INFINITY, "EOS masked before any value");

    // After committing a complete value, EOS becomes allowed.
    st.accept(b"true");
    let mut logits = vec![0.0f32; 6];
    mask.apply(&st, &mut logits);
    assert_eq!(logits[4], 0.0, "EOS allowed once the value is complete");
}

#[test]
fn custom_grammar_enum_choice() {
    // A grammar that only permits one of three exact words — the classic
    // classification / tool-routing use case.
    let g = Arc::new(Grammar::parse(r#"root ::= "yes" | "no" | "maybe""#).unwrap());
    assert!(accepts_complete(&g, "yes"));
    assert!(accepts_complete(&g, "maybe"));
    assert!(!accepts_complete(&g, "y"));
    assert!(!accepts_complete(&g, "yesno"));
}