Merge rust-embedded-community#23

23: Attempt to add support for de/serializing maps r=japaric a=dflemstr

This enables constructing map-like types (a PR for that to heapless will follow)

Co-authored-by: David Flemström <dflemstr@spotify.com>

Author: bors[bot]

src/de/mod.rs

@@ -527,22 +527,7 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
         self.deserialize_seq(visitor)
     }
 
-    /// Unsupported. Can’t make an arbitrary-sized map in no-std. Use a struct with a
-    /// known format, or implement a custom map deserializer / visitor:
-    /// https://serde.rs/deserialize-map.html
-    fn deserialize_map<V>(self, _visitor: V) -> Result<V::Value>
-    where
-        V: Visitor<'de>,
-    {
-        unreachable!()
-    }
-
-    fn deserialize_struct<V>(
-        self,
-        _name: &'static str,
-        _fields: &'static [&'static str],
-        visitor: V,
-    ) -> Result<V::Value>
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>
     where
         V: Visitor<'de>,
     {
@@ -561,6 +546,18 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
         }
     }
 
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_map(visitor)
+    }
+
     fn deserialize_enum<V>(
         self,
         _name: &'static str,

src/ser/map.rs

@@ -0,0 +1,56 @@
+use serde::ser;
+
+use heapless::ArrayLength;
+
+use crate::ser::{Error, Result, Serializer};
+
+pub struct SerializeMap<'a, B>
+where
+    B: ArrayLength<u8>,
+{
+    ser: &'a mut Serializer<B>,
+    first: bool,
+}
+
+impl<'a, B> SerializeMap<'a, B>
+where
+    B: ArrayLength<u8>,
+{
+    pub(crate) fn new(ser: &'a mut Serializer<B>) -> Self {
+        SerializeMap { ser, first: true }
+    }
+}
+
+impl<'a, B> ser::SerializeMap for SerializeMap<'a, B>
+where
+    B: ArrayLength<u8>,
+{
+    type Ok = ();
+    type Error = Error;
+
+    fn end(self) -> Result<Self::Ok> {
+        self.ser.buf.push(b'}')?;
+        Ok(())
+    }
+
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<()>
+    where
+        T: ser::Serialize,
+    {
+        if !self.first {
+            self.ser.buf.push(b',')?;
+        }
+        self.first = false;
+        key.serialize(&mut *self.ser)?;
+        self.ser.buf.extend_from_slice(b":")?;
+        Ok(())
+    }
+
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<()>
+    where
+        T: ser::Serialize,
+    {
+        value.serialize(&mut *self.ser)?;
+        Ok(())
+    }
+}

src/ser/mod.rs

@@ -6,9 +6,11 @@ use serde::ser;
 
 use heapless::{consts::*, String, Vec};
 
+use self::map::SerializeMap;
 use self::seq::SerializeSeq;
 use self::struct_::SerializeStruct;
 
+mod map;
 mod seq;
 mod struct_;
 
@@ -142,7 +144,7 @@ where
     type SerializeTuple = SerializeSeq<'a, B>;
     type SerializeTupleStruct = Unreachable;
     type SerializeTupleVariant = Unreachable;
-    type SerializeMap = Unreachable;
+    type SerializeMap = SerializeMap<'a, B>;
     type SerializeStruct = SerializeStruct<'a, B>;
     type SerializeStructVariant = Unreachable;
 
@@ -301,7 +303,9 @@ where
     }
 
     fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
-        unreachable!()
+        self.buf.push(b'{')?;
+
+        Ok(SerializeMap::new(self))
     }
 
     fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {

src/ser/struct_.rs

@@ -8,16 +8,16 @@ pub struct SerializeStruct<'a, B>
 where
     B: ArrayLength<u8>,
 {
-    de: &'a mut Serializer<B>,
+    ser: &'a mut Serializer<B>,
     first: bool,
 }
 
 impl<'a, B> SerializeStruct<'a, B>
 where
     B: ArrayLength<u8>,
 {
-    pub(crate) fn new(de: &'a mut Serializer<B>) -> Self {
-        SerializeStruct { de, first: true }
+    pub(crate) fn new(ser: &'a mut Serializer<B>) -> Self {
+        SerializeStruct { ser, first: true }
     }
 }
 
@@ -34,21 +34,21 @@ where
     {
         // XXX if `value` is `None` we not produce any output for this field
         if !self.first {
-            self.de.buf.push(b',')?;
+            self.ser.buf.push(b',')?;
         }
         self.first = false;
 
-        self.de.buf.push(b'"')?;
-        self.de.buf.extend_from_slice(key.as_bytes())?;
-        self.de.buf.extend_from_slice(b"\":")?;
+        self.ser.buf.push(b'"')?;
+        self.ser.buf.extend_from_slice(key.as_bytes())?;
+        self.ser.buf.extend_from_slice(b"\":")?;
 
-        value.serialize(&mut *self.de)?;
+        value.serialize(&mut *self.ser)?;
 
         Ok(())
     }
 
     fn end(self) -> Result<Self::Ok> {
-        self.de.buf.push(b'}')?;
+        self.ser.buf.push(b'}')?;
         Ok(())
     }
 }