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
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
use std::fmt;

use crate::backend::{Backend, HasBindCollector};
use crate::query_builder::{BindCollector, QueryBuilder};
use crate::result::QueryResult;
use crate::serialize::ToSql;
use crate::sql_types::HasSqlType;

#[allow(missing_debug_implementations)]
/// The primary type used when walking a Diesel AST during query execution.
///
/// Executing a query is generally done in multiple passes. This list includes,
/// but is not limited to:
///
/// - Generating the SQL
/// - Collecting and serializing bound values (sent separately from the SQL)
/// - Determining if a query is safe to store in the prepared statement cache
///
/// When adding a new type that is used in a Diesel AST, you don't need to care
/// about which specific passes are being performed, nor is there any way for
/// you to find out what the current pass is. You should simply call the
/// relevant methods and trust that they will be a no-op if they're not relevant
/// to the current pass.
pub struct AstPass<'a, 'b, DB>
where
    DB: Backend,
    DB::QueryBuilder: 'a,
    <DB as HasBindCollector<'a>>::BindCollector: 'a,
    DB::MetadataLookup: 'a,
    'b: 'a,
{
    internals: AstPassInternals<'a, 'b, DB>,
    backend: &'b DB,
}

impl<'a, 'b, DB> AstPass<'a, 'b, DB>
where
    DB: Backend,
    'b: 'a,
{
    pub(crate) fn to_sql(
        query_builder: &'a mut DB::QueryBuilder,
        options: &'a mut AstPassToSqlOptions,
        backend: &'b DB,
    ) -> Self {
        AstPass {
            internals: AstPassInternals::ToSql(query_builder, options),
            backend,
        }
    }

    pub(crate) fn collect_binds(
        collector: &'a mut <DB as HasBindCollector<'b>>::BindCollector,
        metadata_lookup: &'a mut DB::MetadataLookup,
        backend: &'b DB,
    ) -> Self {
        AstPass {
            internals: AstPassInternals::CollectBinds {
                collector,
                metadata_lookup,
            },
            backend,
        }
    }

    pub(crate) fn is_safe_to_cache_prepared(result: &'a mut bool, backend: &'b DB) -> Self {
        AstPass {
            internals: AstPassInternals::IsSafeToCachePrepared(result),
            backend,
        }
    }

    pub(crate) fn debug_binds(formatter: &'a mut Vec<&'b dyn fmt::Debug>, backend: &'b DB) -> Self {
        AstPass {
            internals: AstPassInternals::DebugBinds(formatter),
            backend,
        }
    }

    /// Does running this AST pass have any effect?
    ///
    /// The result will be set to `false` if any method that generates SQL
    /// is called.
    pub(crate) fn is_noop(result: &'a mut bool, backend: &'b DB) -> Self {
        AstPass {
            internals: AstPassInternals::IsNoop(result),
            backend,
        }
    }

    #[cfg(feature = "sqlite")]
    pub(crate) fn skip_from(&mut self, value: bool) {
        if let AstPassInternals::ToSql(_, ref mut options) = self.internals {
            options.skip_from = value
        }
    }

    /// Call this method whenever you pass an instance of `AstPass` by value.
    ///
    /// Effectively copies `self`, with a narrower lifetime. When passing a
    /// reference or a mutable reference, this is normally done by rust
    /// implicitly. This is why you can pass `&mut Foo` to multiple functions,
    /// even though mutable references are not `Copy`. However, this is only
    /// done implicitly for references. For structs with lifetimes it must be
    /// done explicitly. This method matches the semantics of what Rust would do
    /// implicitly if you were passing a mutable reference
    pub fn reborrow(&'_ mut self) -> AstPass<'_, 'b, DB> {
        let internals = match self.internals {
            AstPassInternals::ToSql(ref mut builder, ref mut options) => {
                AstPassInternals::ToSql(&mut **builder, &mut **options)
            }
            AstPassInternals::CollectBinds {
                ref mut collector,
                ref mut metadata_lookup,
            } => AstPassInternals::CollectBinds {
                collector: &mut **collector,
                metadata_lookup: &mut **metadata_lookup,
            },
            AstPassInternals::IsSafeToCachePrepared(ref mut result) => {
                AstPassInternals::IsSafeToCachePrepared(&mut **result)
            }
            AstPassInternals::DebugBinds(ref mut f) => AstPassInternals::DebugBinds(&mut **f),
            AstPassInternals::IsNoop(ref mut result) => AstPassInternals::IsNoop(&mut **result),
        };
        AstPass {
            internals,
            backend: self.backend,
        }
    }

    /// Mark the current query being constructed as unsafe to store in the
    /// prepared statement cache.
    ///
    /// Diesel caches prepared statements as much as possible. However, it is
    /// important to ensure that this doesn't result in unbounded memory usage
    /// on the database server. To ensure this is the case, any logical query
    /// which could generate a potentially unbounded number of prepared
    /// statements *must* call this method. Examples of AST nodes which do this
    /// are:
    ///
    /// - `SqlLiteral`. We have no way of knowing if the SQL string was
    ///   constructed dynamically or not, so we must assume it was dynamic.
    /// - `EqAny` when passed a Rust `Vec`. The `IN` operator requires one bind
    ///   parameter per element, meaning that the query could generate up to
    ///   `usize` unique prepared statements.
    /// - `InsertStatement`. Unbounded due to the variable number of records
    ///   being inserted generating unique SQL.
    /// - `UpdateStatement`. The number of potential queries is actually
    ///   technically bounded, but the upper bound is the number of columns on
    ///   the table factorial which is too large to be safe.
    pub fn unsafe_to_cache_prepared(&mut self) {
        if let AstPassInternals::IsSafeToCachePrepared(ref mut result) = self.internals {
            **result = false
        }
    }

    /// Push the given SQL string on the end of the query being constructed.
    ///
    /// # Example
    ///
    /// ```rust
    /// # use diesel::query_builder::{QueryFragment, AstPass};
    /// # use diesel::backend::Backend;
    /// # use diesel::QueryResult;
    /// # struct And<Left, Right> { left: Left, right: Right }
    /// impl<Left, Right, DB> QueryFragment<DB> for And<Left, Right>
    /// where
    ///     DB: Backend,
    ///     Left: QueryFragment<DB>,
    ///     Right: QueryFragment<DB>,
    /// {
    ///     fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()> {
    ///         self.left.walk_ast(out.reborrow())?;
    ///         out.push_sql(" AND ");
    ///         self.right.walk_ast(out.reborrow())?;
    ///         Ok(())
    ///     }
    /// }
    /// # fn main() {}
    /// ```
    pub fn push_sql(&mut self, sql: &str) {
        match self.internals {
            AstPassInternals::ToSql(ref mut builder, _) => builder.push_sql(sql),
            AstPassInternals::IsNoop(ref mut result) => **result = false,
            _ => {}
        }
    }

    /// Push the given SQL identifier on the end of the query being constructed.
    ///
    /// The identifier will be quoted using the rules specific to the backend
    /// the query is being constructed for.
    pub fn push_identifier(&mut self, identifier: &str) -> QueryResult<()> {
        match self.internals {
            AstPassInternals::ToSql(ref mut builder, _) => builder.push_identifier(identifier)?,
            AstPassInternals::IsNoop(ref mut result) => **result = false,
            _ => {}
        }
        Ok(())
    }

    /// Push a value onto the given query to be sent separate from the SQL
    ///
    /// This method affects multiple AST passes. It should be called at the
    /// point in the query where you'd want the parameter placeholder (`$1` on
    /// PG, `?` on other backends) to be inserted.
    pub fn push_bind_param<T, U>(&mut self, bind: &'b U) -> QueryResult<()>
    where
        DB: HasSqlType<T>,
        U: ToSql<T, DB>,
    {
        match self.internals {
            AstPassInternals::ToSql(ref mut out, _) => out.push_bind_param(),
            AstPassInternals::CollectBinds {
                ref mut collector,
                ref mut metadata_lookup,
            } => collector.push_bound_value(bind, metadata_lookup)?,
            AstPassInternals::DebugBinds(ref mut f) => {
                f.push(bind);
            }
            AstPassInternals::IsNoop(ref mut result) => **result = false,
            _ => {}
        }
        Ok(())
    }

    pub(crate) fn push_bind_param_value_only<T, U>(&mut self, bind: &'b U) -> QueryResult<()>
    where
        DB: HasSqlType<T>,
        U: ToSql<T, DB>,
    {
        match self.internals {
            AstPassInternals::CollectBinds { .. } | AstPassInternals::DebugBinds(..) => {
                self.push_bind_param(bind)?
            }
            AstPassInternals::ToSql(ref mut out, _) => {
                out.push_bind_param_value_only();
            }
            _ => {}
        }
        Ok(())
    }

    /// Get information about the backend that will consume this query
    #[cfg_attr(
        not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"),
        doc(hidden)
    )] // This is used by the `sql_function` macro
    #[cfg_attr(
        doc_cfg,
        doc(cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))
    )]
    pub fn backend(&self) -> &DB {
        self.backend
    }

    /// Get if the query should be rendered with from clauses or not
    #[cfg_attr(
        not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"),
        doc(hidden)
    )] // This is used by the `__diesel_column` macro
    #[cfg_attr(
        doc_cfg,
        doc(cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))
    )]
    pub fn should_skip_from(&self) -> bool {
        if let AstPassInternals::ToSql(_, ref options) = self.internals {
            options.skip_from
        } else {
            false
        }
    }
}

#[allow(missing_debug_implementations)]
/// This is separate from the struct to cause the enum to be opaque, forcing
/// usage of the methods provided rather than matching on the enum directly.
/// This essentially mimics the capabilities that would be available if
/// `AstPass` were a trait.
enum AstPassInternals<'a, 'b, DB>
where
    DB: Backend,
    DB::QueryBuilder: 'a,
    <DB as HasBindCollector<'a>>::BindCollector: 'a,
    DB::MetadataLookup: 'a,
    'b: 'a,
{
    ToSql(&'a mut DB::QueryBuilder, &'a mut AstPassToSqlOptions),
    CollectBinds {
        collector: &'a mut <DB as HasBindCollector<'b>>::BindCollector,
        metadata_lookup: &'a mut DB::MetadataLookup,
    },
    IsSafeToCachePrepared(&'a mut bool),
    DebugBinds(&'a mut Vec<&'b dyn fmt::Debug>),
    IsNoop(&'a mut bool),
}

#[diesel_derives::__diesel_public_if(
    feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"
)]
#[allow(missing_debug_implementations)]
#[allow(missing_copy_implementations)]
#[derive(Default)]
/// This is used to pass down additional settings to the `AstPass`
/// when rendering the sql string.
pub(crate) struct AstPassToSqlOptions {
    skip_from: bool,
}