alef 0.82.0

Opinionated polyglot binding generator for Rust libraries
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
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169

//! SECURITY. `rust_default_via_source_deserialize` (via `default_value_for_field_in_type`) builds
//! a minimal JSON probe object and deserializes it through the owning type's real `Deserialize`
//! impl to recover a `#[serde(default = "path")]` field's true value. Every sibling field must be
//! present in that probe UNLESS serde itself would genuinely fill it when its wire key is absent
//! — its own field-level serde default, a container-level `#[serde(default)]`, or `Option<T>`.
//!
//! The predicate used to also treat `sibling.typed_default.is_some()` as such a signal. That is
//! wrong: `#[derive(Default)]` seeds `typed_default = Some(DefaultValue::Empty)` on *every* field
//! of the container (`extract::extractor::types::extract_struct`), including fields with no
//! serde attribute at all, so the old predicate was true for essentially any field on a
//! `derive(Default)` type. That silently dropped every required sibling from the probe, leaving
//! `placeholders` empty and the caller emitting `serde_json::from_str(r#"{}"#)`, which panics at
//! runtime the first time the type is actually missing a required field. `sibling.default` is the
//! narrower, durable signal `extract::extractor::helpers::fields::extract_field` sets only from a
//! real per-field serde default attribute, unaffected by the later `#[derive(Default)]`/manual
//! `impl Default` overwrite of `typed_default` — see
//! `backends::go::gen_bindings::types::helpers::needs_omitempty_pointer`, which gates the
//! equivalent Go decision on the same two facts and documents `has_default` as inadmissible.
//!
//! Lives in its own module because `tests/defaults.rs` next door is already pinned at the repo's
//! 1,000-line file-size cap by the ratchet baseline and must not grow. ~keep

use super::*;

/// A type shaped like a config struct that derives `Default` and also carries a genuine
/// `#[serde(default = "path")]` field. `target` is always the field being solved for.
///
/// `target` carries both `default` (the raw attribute text) and `typed_default`
/// (`FunctionCall`), mirroring `extract::extractor::helpers::fields::extract_field`, which
/// always sets both together from the same `#[serde(default = "path")]` attribute — never
/// only one. `default.is_some()` is what makes the loop in
/// `rust_default_via_source_deserialize` correctly omit `target` itself from its own probe
/// JSON (it is being solved for, not a placeholder), so a fixture missing it here would
/// silently add a spurious `"count":0` placeholder and invalidate every expected string below.
fn derived_config_type(siblings: Vec<FieldDef>) -> TypeDef {
    let target = FieldDef {
        default: Some("serde(default = \"mylib::default_count\")".to_string()),
        typed_default: Some(DefaultValue::FunctionCall("mylib::default_count".to_string())),
        ..make_field("count", TypeRef::Primitive(PrimitiveType::U32))
    };
    let mut fields = siblings;
    fields.push(target);
    TypeDef {
        name: "DerivedConfig".to_string(),
        rust_path: "mylib::DerivedConfig".to_string(),
        has_default: true,
        has_serde: true,
        fields,
        ..Default::default()
    }
}

fn target_field(typ: &TypeDef) -> &FieldDef {
    typ.fields.iter().find(|f| f.name == "count").unwrap()
}

/// Pins the bug this fix targets. `label` is a required, non-`Option` field with no serde
/// attribute of its own — exactly what every plain field on a `derive(Default)` struct looks
/// like once extraction seeds `typed_default = Some(Empty)` for it. It must still be emitted
/// into the probe JSON with a real placeholder, not silently omitted.
///
/// Against the predicate this fix replaces (`sibling.typed_default.is_some() ||
/// sibling.default.is_some()`), `label` has `typed_default = Some(Empty)` and would be treated
/// as already-defaulted, omitting it from the probe entirely and rendering
/// `serde_json::from_str::<mylib::DerivedConfig>(r#"{}"#)...count` instead of the value
/// asserted below — the exact empty-object probe that panics at runtime on real construction.
#[test]
fn derive_default_seeded_empty_is_not_treated_as_a_serde_default() {
    let label = FieldDef {
        typed_default: Some(DefaultValue::Empty),
        ..make_field("label", TypeRef::String)
    };
    let typ = derived_config_type(vec![label]);

    let rendered = default_value_for_field_in_type(target_field(&typ), "rust", &typ);

    assert_eq!(
        rendered,
        "serde_json::from_str::<mylib::DerivedConfig>(r#\"{\"label\":\"\"}\"#)\
         .expect(\"alef-generated default JSON for `DerivedConfig` failed to deserialize\").count",
        "a required sibling seeded `Empty` only by `#[derive(Default)]` must still get a \
         placeholder, not be dropped from the probe: {rendered}"
    );
}

/// A container-level `#[serde(default)]` makes every field on the type absent-tolerant, so a
/// sibling with no attribute of its own may still be omitted from the probe.
#[test]
fn container_level_serde_default_omits_an_unmarked_sibling() {
    let label = make_field("label", TypeRef::String);
    let mut typ = derived_config_type(vec![label]);
    typ.serde_container_default = true;

    let rendered = default_value_for_field_in_type(target_field(&typ), "rust", &typ);

    assert_eq!(
        rendered,
        "serde_json::from_str::<mylib::DerivedConfig>(r#\"{}\"#)\
         .expect(\"alef-generated default JSON for `DerivedConfig` failed to deserialize\").count",
        "a container-level `#[serde(default)]` must omit every sibling, including one with no \
         attribute of its own: {rendered}"
    );
}

/// A field's own `#[serde(default = "path")]` is the genuine signal `sibling.default` records;
/// that sibling may be omitted from the probe.
#[test]
fn field_level_named_serde_default_omits_its_own_sibling() {
    let user_agent = FieldDef {
        default: Some("serde(default = \"mylib::default_user_agent\")".to_string()),
        typed_default: Some(DefaultValue::FunctionCall("mylib::default_user_agent".to_string())),
        ..make_field("user_agent", TypeRef::String)
    };
    let typ = derived_config_type(vec![user_agent]);

    let rendered = default_value_for_field_in_type(target_field(&typ), "rust", &typ);

    assert_eq!(
        rendered,
        "serde_json::from_str::<mylib::DerivedConfig>(r#\"{}\"#)\
         .expect(\"alef-generated default JSON for `DerivedConfig` failed to deserialize\").count",
        "a field carrying its own named serde default must be omitted from the probe: {rendered}"
    );
}

/// `Option<T>` fields are always absent-tolerant regardless of any serde default attribute.
#[test]
fn optional_sibling_is_omitted_regardless_of_default() {
    let nickname = FieldDef {
        optional: true,
        ..make_field("nickname", TypeRef::Optional(Box::new(TypeRef::String)))
    };
    let typ = derived_config_type(vec![nickname]);

    let rendered = default_value_for_field_in_type(target_field(&typ), "rust", &typ);

    assert_eq!(
        rendered,
        "serde_json::from_str::<mylib::DerivedConfig>(r#\"{}\"#)\
         .expect(\"alef-generated default JSON for `DerivedConfig` failed to deserialize\").count",
        "an Option<T> sibling must be omitted from the probe: {rendered}"
    );
}

/// When the narrowed predicate correctly treats a nested named-type sibling as genuinely
/// required (no own serde default, not optional, not covered by a container default), and that
/// type has no safe JSON placeholder, generation must fail loudly rather than silently emit an
/// empty-object probe that panics at runtime on the first real construction.
#[test]
fn required_nested_named_sibling_fails_generation_instead_of_probing_empty() {
    let owner = FieldDef {
        typed_default: Some(DefaultValue::Empty),
        ..make_field("owner", TypeRef::Named("Author".to_string()))
    };
    let typ = derived_config_type(vec![owner]);

    let message = default_value_for_field_in_type(target_field(&typ), "rust", &typ);

    assert!(
        message.starts_with("compile_error!"),
        "a required sibling with no safe placeholder must fail generation, not probe `{{}}`: {message}"
    );
    for needle in ["mylib", "DerivedConfig", "count", "mylib::default_count"] {
        assert!(
            message.contains(needle),
            "the failure must name `{needle}` so the author can act on it: {message}"
        );
    }
}