#
cargo/util/context/
de.rs

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    //! Support for deserializing configuration via `serde`

    use crate::util::context::value;
    use crate::util::context::{ConfigError, ConfigKey, GlobalContext};
    use crate::util::context::{ConfigValue as CV, Definition, Value};
    use serde::{de, de::IntoDeserializer};
    use std::collections::HashSet;
    use std::vec;

    /// Serde deserializer used to convert config values to a target type using
    /// [`GlobalContext::get`].
    #[derive(Clone)]
    pub(super) struct Deserializer<'gctx> {
        pub(super) gctx: &'gctx GlobalContext,
        /// The current key being deserialized.
        pub(super) key: ConfigKey,
        /// Whether or not this key part is allowed to be an inner table. For
        /// example, `profile.dev.build-override` needs to check if
        /// CARGO_PROFILE_DEV_BUILD_OVERRIDE_ prefixes exist. But
        /// CARGO_BUILD_TARGET should not check for prefixes because it would
        /// collide with CARGO_BUILD_TARGET_DIR. See `ConfigMapAccess` for
        /// details.
        pub(super) env_prefix_ok: bool,
    }

    macro_rules! deserialize_method {
        ($method:ident, $visit:ident, $getter:ident) => {
            fn $method<V>(self, visitor: V) -> Result<V::Value, Self::Error>
            where
                V: de::Visitor<'de>,
            {
                let v = self
                    .gctx
                    .$getter(&self.key)?
                    .ok_or_else(|| ConfigError::missing(&self.key))?;
                let Value { val, definition } = v;
                let res: Result<V::Value, ConfigError> = visitor.$visit(val);
                res.map_err(|e| e.with_key_context(&self.key, Some(definition)))
            }
        };
    }

    impl<'de, 'gctx> de::Deserializer<'de> for Deserializer<'gctx> {
        type Error = ConfigError;

        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            let cv = self.gctx.get_cv_with_env(&self.key)?;
            if let Some(cv) = cv {
                let res: (Result<V::Value, ConfigError>, Definition) = match cv {
                    CV::Integer(i, def) => (visitor.visit_i64(i), def),
                    CV::String(s, def) => (visitor.visit_string(s), def),
                    CV::List(_, def) => (visitor.visit_seq(ConfigSeqAccess::new(self.clone())?), def),
                    CV::Table(_, def) => (
                        visitor.visit_map(ConfigMapAccess::new_map(self.clone())?),
                        def,
                    ),
                    CV::Boolean(b, def) => (visitor.visit_bool(b), def),
                };
                let (res, def) = res;
                return res.map_err(|e| e.with_key_context(&self.key, Some(def)));
            }

            // The effect here is the same as in `deserialize_option`.
            if self.gctx.has_key(&self.key, self.env_prefix_ok)? {
                return visitor.visit_some(self);
            }

            Err(ConfigError::missing(&self.key))
        }

        deserialize_method!(deserialize_bool, visit_bool, get_bool);
        deserialize_method!(deserialize_i8, visit_i64, get_integer);
        deserialize_method!(deserialize_i16, visit_i64, get_integer);
        deserialize_method!(deserialize_i32, visit_i64, get_integer);
        deserialize_method!(deserialize_i64, visit_i64, get_integer);
        deserialize_method!(deserialize_u8, visit_i64, get_integer);
        deserialize_method!(deserialize_u16, visit_i64, get_integer);
        deserialize_method!(deserialize_u32, visit_i64, get_integer);
        deserialize_method!(deserialize_u64, visit_i64, get_integer);
        deserialize_method!(deserialize_string, visit_string, get_string_priv);

        fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            if self.gctx.has_key(&self.key, self.env_prefix_ok)? {
                visitor.visit_some(self)
            } else {
                // Treat missing values as `None`.
                visitor.visit_none()
            }
        }

        fn deserialize_struct<V>(
            self,
            name: &'static str,
            fields: &'static [&'static str],
            visitor: V,
        ) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            // Match on the magical struct name/field names that are passed in to
            // detect when we're deserializing `Value<T>`.
            //
            // See more comments in `value.rs` for the protocol used here.
            if name == value::NAME && fields == value::FIELDS {
                return visitor.visit_map(ValueDeserializer::new(self)?);
            }
            visitor.visit_map(ConfigMapAccess::new_struct(self, fields)?)
        }

        fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_map(ConfigMapAccess::new_map(self)?)
        }

        fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_seq(ConfigSeqAccess::new(self)?)
        }

        fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_seq(ConfigSeqAccess::new(self)?)
        }

        fn deserialize_tuple_struct<V>(
            self,
            _name: &'static str,
            _len: usize,
            visitor: V,
        ) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_seq(ConfigSeqAccess::new(self)?)
        }

        fn deserialize_newtype_struct<V>(
            self,
            name: &'static str,
            visitor: V,
        ) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            let merge = if name == "StringList" {
                true
            } else if name == "UnmergedStringList" {
                false
            } else {
                return visitor.visit_newtype_struct(self);
            };

            let vals = self.gctx.get_list_or_string(&self.key, merge)?;
            let vals: Vec<String> = vals.into_iter().map(|vd| vd.0).collect();
            visitor.visit_newtype_struct(vals.into_deserializer())
        }

        fn deserialize_enum<V>(
            self,
            _name: &'static str,
            _variants: &'static [&'static str],
            visitor: V,
        ) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            let value = self
                .gctx
                .get_string_priv(&self.key)?
                .ok_or_else(|| ConfigError::missing(&self.key))?;

            let Value { val, definition } = value;
            visitor
                .visit_enum(val.into_deserializer())
                .map_err(|e: ConfigError| e.with_key_context(&self.key, Some(definition)))
        }

        // These aren't really supported, yet.
        serde::forward_to_deserialize_any! {
            f32 f64 char str bytes
            byte_buf unit unit_struct
            identifier ignored_any
        }
    }

    struct ConfigMapAccess<'gctx> {
        de: Deserializer<'gctx>,
        /// The fields that this map should deserialize.
        fields: Vec<KeyKind>,
        /// Current field being deserialized.
        field_index: usize,
    }

    #[derive(Debug, PartialEq, Eq, Hash)]
    enum KeyKind {
        Normal(String),
        CaseSensitive(String),
    }

    impl<'gctx> ConfigMapAccess<'gctx> {
        fn new_map(de: Deserializer<'gctx>) -> Result<ConfigMapAccess<'gctx>, ConfigError> {
            let mut fields = Vec::new();
            if let Some(mut v) = de.gctx.get_table(&de.key)? {
                // `v: Value<HashMap<String, CV>>`
                for (key, _value) in v.val.drain() {
                    fields.push(KeyKind::CaseSensitive(key));
                }
            }
            if de.gctx.cli_unstable().advanced_env {
                // `CARGO_PROFILE_DEV_PACKAGE_`
                let env_prefix = format!("{}_", de.key.as_env_key());
                for env_key in de.gctx.env_keys() {
                    // `CARGO_PROFILE_DEV_PACKAGE_bar_OPT_LEVEL = 3`
                    if let Some(rest) = env_key.strip_prefix(&env_prefix) {
                        // `rest = bar_OPT_LEVEL`
                        let part = rest.splitn(2, '_').next().unwrap();
                        // `part = "bar"`
                        fields.push(KeyKind::CaseSensitive(part.to_string()));
                    }
                }
            }
            Ok(ConfigMapAccess {
                de,
                fields,
                field_index: 0,
            })
        }

        fn new_struct(
            de: Deserializer<'gctx>,
            given_fields: &'static [&'static str],
        ) -> Result<ConfigMapAccess<'gctx>, ConfigError> {
            let table = de.gctx.get_table(&de.key)?;

            // Assume that if we're deserializing a struct it exhaustively lists all
            // possible fields on this key that we're *supposed* to use, so take
            // this opportunity to warn about any keys that aren't recognized as
            // fields and warn about them.
            if let Some(v) = table.as_ref() {
                let unused_keys = v
                    .val
                    .iter()
                    .filter(|(k, _v)| !given_fields.iter().any(|gk| gk == k));
                for (unused_key, unused_value) in unused_keys {
                    de.gctx.shell().warn(format!(
                        "unused config key `{}.{}` in `{}`",
                        de.key,
                        unused_key,
                        unused_value.definition()
                    ))?;
                }
            }

            let mut fields = HashSet::new();

            // If the caller is interested in a field which we can provide from
            // the environment, get it from there.
            for field in given_fields {
                let mut field_key = de.key.clone();
                field_key.push(field);
                for env_key in de.gctx.env_keys() {
                    let Some(nested_field) = env_key.strip_prefix(field_key.as_env_key()) else {
                        continue;
                    };
                    // This distinguishes fields that share the same prefix.
                    // For example, when env_key is UNSTABLE_GITOXIDE_FETCH
                    // and field_key is UNSTABLE_GIT, the field shouldn't be
                    // added because `unstable.gitoxide.fetch` doesn't
                    // belong to `unstable.git` struct.
                    if nested_field.is_empty() || nested_field.starts_with('_') {
                        fields.insert(KeyKind::Normal(field.to_string()));
                    }
                }
            }

            // Add everything from the config table we're interested in that we
            // haven't already provided via an environment variable
            if let Some(v) = table {
                for key in v.val.keys() {
                    fields.insert(KeyKind::Normal(key.clone()));
                }
            }

            Ok(ConfigMapAccess {
                de,
                fields: fields.into_iter().collect(),
                field_index: 0,
            })
        }
    }

    impl<'de, 'gctx> de::MapAccess<'de> for ConfigMapAccess<'gctx> {
        type Error = ConfigError;

        fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
        where
            K: de::DeserializeSeed<'de>,
        {
            if self.field_index >= self.fields.len() {
                return Ok(None);
            }
            let field = match &self.fields[self.field_index] {
                KeyKind::Normal(s) | KeyKind::CaseSensitive(s) => s.as_str(),
            };
            seed.deserialize(field.into_deserializer()).map(Some)
        }

        fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
        where
            V: de::DeserializeSeed<'de>,
        {
            let field = &self.fields[self.field_index];
            self.field_index += 1;
            // Set this as the current key in the deserializer.
            let field = match field {
                KeyKind::Normal(field) => {
                    self.de.key.push(field);
                    field
                }
                KeyKind::CaseSensitive(field) => {
                    self.de.key.push_sensitive(field);
                    field
                }
            };
            // Env vars that are a prefix of another with a dash/underscore cannot
            // be supported by our serde implementation, so check for them here.
            // Example:
            //     CARGO_BUILD_TARGET
            //     CARGO_BUILD_TARGET_DIR
            // or
            //     CARGO_PROFILE_DEV_DEBUG
            //     CARGO_PROFILE_DEV_DEBUG_ASSERTIONS
            // The `deserialize_option` method does not know the type of the field.
            // If the type is an Option<struct> (like
            // `profile.dev.build-override`), then it needs to check for env vars
            // starting with CARGO_FOO_BAR_. This is a problem for keys like
            // CARGO_BUILD_TARGET because checking for a prefix would incorrectly
            // match CARGO_BUILD_TARGET_DIR. `deserialize_option` would have no
            // choice but to call `visit_some()` which would then fail if
            // CARGO_BUILD_TARGET isn't set. So we check for these prefixes and
            // disallow them here.
            let env_prefix = format!("{}_", field).replace('-', "_");
            let env_prefix_ok = !self.fields.iter().any(|field| {
                let field = match field {
                    KeyKind::Normal(s) | KeyKind::CaseSensitive(s) => s.as_str(),
                };
                field.replace('-', "_").starts_with(&env_prefix)
            });

            let result = seed
                .deserialize(Deserializer {
                    gctx: self.de.gctx,
                    key: self.de.key.clone(),
                    env_prefix_ok,
                })
                .map_err(|e| {
                    if !e.is_missing_field() {
                        return e;
                    }
                    e.with_key_context(
                        &self.de.key,
                        self.de
                            .gctx
                            .get_cv_with_env(&self.de.key)
                            .ok()
                            .and_then(|cv| cv.map(|cv| cv.get_definition().clone())),
                    )
                });
            self.de.key.pop();
            result
        }
    }

    struct ConfigSeqAccess {
        list_iter: vec::IntoIter<(String, Definition)>,
    }

    impl ConfigSeqAccess {
        fn new(de: Deserializer<'_>) -> Result<ConfigSeqAccess, ConfigError> {
            let mut res = Vec::new();
            if let Some(v) = de.gctx._get_list(&de.key)? {
                res.extend(v.val);
            }

            de.gctx.get_env_list(&de.key, &mut res)?;

            Ok(ConfigSeqAccess {
                list_iter: res.into_iter(),
            })
        }
    }

    impl<'de> de::SeqAccess<'de> for ConfigSeqAccess {
        type Error = ConfigError;

        fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Self::Error>
        where
            T: de::DeserializeSeed<'de>,
        {
            match self.list_iter.next() {
                // TODO: add `def` to error?
                Some((value, def)) => {
                    // This might be a String or a Value<String>.
                    // ValueDeserializer will handle figuring out which one it is.
                    let maybe_value_de = ValueDeserializer::new_with_string(value, def);
                    seed.deserialize(maybe_value_de).map(Some)
                }
                None => Ok(None),
            }
        }
    }

    /// This is a deserializer that deserializes into a `Value<T>` for
    /// configuration.
    ///
    /// This is a special deserializer because it deserializes one of its struct
    /// fields into the location that this configuration value was defined in.
    ///
    /// See more comments in `value.rs` for the protocol used here.
    struct ValueDeserializer<'gctx> {
        hits: u32,
        definition: Definition,
        /// The deserializer, used to actually deserialize a Value struct.
        /// This is `None` if deserializing a string.
        de: Option<Deserializer<'gctx>>,
        /// A string value to deserialize.
        ///
        /// This is used for situations where you can't address a string via a
        /// TOML key, such as a string inside an array. The `ConfigSeqAccess`
        /// doesn't know if the type it should deserialize to is a `String` or
        /// `Value<String>`, so `ValueDeserializer` needs to be able to handle
        /// both.
        str_value: Option<String>,
    }

    impl<'gctx> ValueDeserializer<'gctx> {
        fn new(de: Deserializer<'gctx>) -> Result<ValueDeserializer<'gctx>, ConfigError> {
            // Figure out where this key is defined.
            let definition = {
                let env = de.key.as_env_key();
                let env_def = Definition::Environment(env.to_string());
                match (de.gctx.env.contains_key(env), de.gctx.get_cv(&de.key)?) {
                    (true, Some(cv)) => {
                        // Both, pick highest priority.
                        if env_def.is_higher_priority(cv.definition()) {
                            env_def
                        } else {
                            cv.definition().clone()
                        }
                    }
                    (false, Some(cv)) => cv.definition().clone(),
                    // Assume it is an environment, even if the key is not set.
                    // This can happen for intermediate tables, like
                    // CARGO_FOO_BAR_* where `CARGO_FOO_BAR` is not set.
                    (_, None) => env_def,
                }
            };
            Ok(ValueDeserializer {
                hits: 0,
                definition,
                de: Some(de),
                str_value: None,
            })
        }

        fn new_with_string(s: String, definition: Definition) -> ValueDeserializer<'gctx> {
            ValueDeserializer {
                hits: 0,
                definition,
                de: None,
                str_value: Some(s),
            }
        }
    }

    impl<'de, 'gctx> de::MapAccess<'de> for ValueDeserializer<'gctx> {
        type Error = ConfigError;

        fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
        where
            K: de::DeserializeSeed<'de>,
        {
            self.hits += 1;
            match self.hits {
                1 => seed
                    .deserialize(value::VALUE_FIELD.into_deserializer())
                    .map(Some),
                2 => seed
                    .deserialize(value::DEFINITION_FIELD.into_deserializer())
                    .map(Some),
                _ => Ok(None),
            }
        }

        fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Self::Error>
        where
            V: de::DeserializeSeed<'de>,
        {
            // If this is the first time around we deserialize the `value` field
            // which is the actual deserializer
            if self.hits == 1 {
                if let Some(de) = &self.de {
                    return seed
                        .deserialize(de.clone())
                        .map_err(|e| e.with_key_context(&de.key, Some(self.definition.clone())));
                } else {
                    return seed
                        .deserialize(self.str_value.as_ref().unwrap().clone().into_deserializer());
                }
            }

            // ... otherwise we're deserializing the `definition` field, so we need
            // to figure out where the field we just deserialized was defined at.
            match &self.definition {
                Definition::Path(path) => {
                    seed.deserialize(Tuple2Deserializer(0i32, path.to_string_lossy()))
                }
                Definition::Environment(env) => {
                    seed.deserialize(Tuple2Deserializer(1i32, env.as_str()))
                }
                Definition::Cli(path) => {
                    let str = path
                        .as_ref()
                        .map(|p| p.to_string_lossy())
                        .unwrap_or_default();
                    seed.deserialize(Tuple2Deserializer(2i32, str))
                }
            }
        }
    }

    // Deserializer is only implemented to handle deserializing a String inside a
    // sequence (like `Vec<String>` or `Vec<Value<String>>`). `Value<String>` is
    // handled by deserialize_struct, and the plain `String` is handled by all the
    // other functions here.
    impl<'de, 'gctx> de::Deserializer<'de> for ValueDeserializer<'gctx> {
        type Error = ConfigError;

        fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_str(&self.str_value.expect("string expected"))
        }

        fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_string(self.str_value.expect("string expected"))
        }

        fn deserialize_struct<V>(
            self,
            name: &'static str,
            fields: &'static [&'static str],
            visitor: V,
        ) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            // Match on the magical struct name/field names that are passed in to
            // detect when we're deserializing `Value<T>`.
            //
            // See more comments in `value.rs` for the protocol used here.
            if name == value::NAME && fields == value::FIELDS {
                return visitor.visit_map(self);
            }
            unimplemented!("only strings and Value can be deserialized from a sequence");
        }

        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_string(self.str_value.expect("string expected"))
        }

        fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: de::Visitor<'de>,
        {
            visitor.visit_unit()
        }

        serde::forward_to_deserialize_any! {
            i8 i16 i32 i64
            u8 u16 u32 u64
            option
            newtype_struct seq tuple tuple_struct map enum bool
            f32 f64 char bytes
            byte_buf unit unit_struct
            identifier
        }
    }

    /// A deserializer which takes two values and deserializes into a tuple of those
    /// two values. This is similar to types like `StrDeserializer` in upstream
    /// serde itself.
    struct Tuple2Deserializer<T, U>(T, U);

    impl<'de, T, U> de::Deserializer<'de> for Tuple2Deserializer<T, U>
    where
        T: IntoDeserializer<'de, ConfigError>,
        U: IntoDeserializer<'de, ConfigError>,
    {
        type Error = ConfigError;

        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, ConfigError>
        where
            V: de::Visitor<'de>,
        {
            struct SeqVisitor<T, U> {
                first: Option<T>,
                second: Option<U>,
            }
            impl<'de, T, U> de::SeqAccess<'de> for SeqVisitor<T, U>
            where
                T: IntoDeserializer<'de, ConfigError>,
                U: IntoDeserializer<'de, ConfigError>,
            {
                type Error = ConfigError;
                fn next_element_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Self::Error>
                where
                    K: de::DeserializeSeed<'de>,
                {
                    if let Some(first) = self.first.take() {
                        return seed.deserialize(first.into_deserializer()).map(Some);
                    }
                    if let Some(second) = self.second.take() {
                        return seed.deserialize(second.into_deserializer()).map(Some);
                    }
                    Ok(None)
                }
            }

            visitor.visit_seq(SeqVisitor {
                first: Some(self.0),
                second: Some(self.1),
            })
        }

        serde::forward_to_deserialize_any! {
            bool u8 u16 u32 u64 i8 i16 i32 i64 f32 f64 char str string seq
            bytes byte_buf map struct option unit newtype_struct
            ignored_any unit_struct tuple_struct tuple enum identifier
        }
    }