api: drop $float as JSON number is OK

2 files changed, 40 insertions, 27 deletions

diff --git a/src/document/store.rs b/src/document/store.rs
index 9075032..1a235b2 100644
--- a/src/document/store.rs
+++ b/src/document/store.rs
@@ -676,14 +676,27 @@ pub(crate) fn write_val_path(
     Ok(writing.retyped)
 }
 
+/// Which values a write writes as the type of what they are written over (`stuck`).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum Sticky {
+    /// None: the value says its type (a type's own media type, a cast).
+    No,
+    /// A number without a fraction over a float: typed JSON says every other type
+    /// itself, but not a float's, as JSON numbers don't keep `2.0` apart from `2` in
+    /// every language.
+    Floats,
+    /// Plain JSON, which has fewer types than Automerge: where it is the JSON form of a
+    /// value of the type there (a string that reads as a timestamp, as base64, a number
+    /// without a fraction over a float, an unsigned integer or a counter, a string over
+    /// a text).
+    All,
+}
+
 /// How a write treats the types of what it writes over.
 pub(crate) struct Writing {
-    /// Types are sticky: the value comes as plain JSON, which has fewer types than
-    /// Automerge, and where it is the JSON form of a value of the type there (a string
-    /// that reads as a timestamp, as base64, a number without a fraction over a float,
-    /// an unsigned integer or a counter, a string over a text), it is written as that
-    /// type (`stuck`). Typed JSON and a type's own media type say the type themselves.
-    pub(crate) sticky: bool,
+    /// Types are sticky: what the value is written as where it is the JSON form of a
+    /// value of the type there.
+    pub(crate) sticky: Sticky,
     /// How sticky timestamps are written in JSON (`typed::TimestampFormat::json`).
     pub(crate) timestamps: TimestampFormat,
     /// Whether the write may change the type of what it writes over; if not, one that
@@ -695,10 +708,10 @@ pub(crate) struct Writing {
 
 impl Writing {
     pub(crate) fn sticky(timestamps: TimestampFormat) -> Self {
-        Self::new(true, timestamps, true)
+        Self::new(Sticky::All, timestamps, true)
     }
 
-    pub(crate) fn new(sticky: bool, timestamps: TimestampFormat, retype: bool) -> Self {
+    pub(crate) fn new(sticky: Sticky, timestamps: TimestampFormat, retype: bool) -> Self {
         Self {
             sticky,
             timestamps,
@@ -760,11 +773,23 @@ fn kind_of(held: &Value<'_>) -> Kind {
 }
 
 /// `value` written as the type of `held`, where it is a JSON form of a value of it
-/// (`Writing::sticky`); None where it isn't (it is written as it is).
-fn stuck(held: &Value<'_>, value: &Val, timestamps: TimestampFormat) -> Option<Val> {
+/// as `sticky` says (`Writing::sticky`); None where it isn't (it is written as it is).
+fn stuck(
+    held: &Value<'_>,
+    value: &Val,
+    sticky: Sticky,
+    timestamps: TimestampFormat,
+) -> Option<Val> {
     let Val::Scalar(scalar) = value else {
         return None;
     };
+    let over_float = matches!(held, Value::Scalar(held) if matches!(held.as_ref(), ScalarValue::F64(_)))
+        && matches!(scalar, ScalarValue::Int(_) | ScalarValue::Uint(_));
+    match sticky {
+        Sticky::No => return None,
+        Sticky::Floats if !over_float => return None,
+        Sticky::Floats | Sticky::All => {}
+    }
     let held = match held {
         Value::Object(ObjType::Text) => {
             return match scalar {
@@ -843,11 +868,7 @@ fn update_of<'v>(
     let Some((held, _)) = holds.first() else {
         return Ok((Update::Anew, Cow::Borrowed(value)));
     };
-    let value = match writing
-        .sticky
-        .then(|| stuck(held, value, writing.timestamps))
-        .flatten()
-    {
+    let value = match stuck(held, value, writing.sticky, writing.timestamps) {
         Some(stuck) => Cow::Owned(stuck),
         None => Cow::Borrowed(value),
     };
@@ -1083,7 +1104,7 @@ pub(crate) fn cast_path(
         .as_ref()
         .ok_or_else(|| not_castable(format!("{} is cast to nothing", held.kind.name())))?;
     let cast = typed::cast(held.kind, value, to, timestamps).map_err(not_castable)?;
-    write_val_path(doc, path, &cast, Writing::new(false, timestamps, true))
+    write_val_path(doc, path, &cast, Writing::new(Sticky::No, timestamps, true))
 }
 
 /// Inserts `value` into a list: `path` ends in the index it goes to (the items from
diff --git a/src/document/typed.rs b/src/document/typed.rs
index 7f6e0cc..def06df 100644
--- a/src/document/typed.rs
+++ b/src/document/typed.rs
@@ -224,9 +224,9 @@ pub(crate) struct JsonForm {
 // Typed JSON is plain JSON but for what plain JSON shows as another type: a single-key
 // object whose key is a tag names it. `{"$uint": 5}`, `{"$counter": 5}`,
 // `{"$timestamp": "2026-11-01T21:50:20.345Z"}` (in the timestamp format asked),
-// `{"$bytes": "<base64>"}`, `{"$float": 2}` (a float without a fraction, which JSON
-// numbers don't keep apart from integers in every language), `{"$text": "…"}` (an
-// Automerge text). A map whose only key starts with `$` is `{"$map": {…}}`, so that
+// `{"$bytes": "<base64>"}`, `{"$text": "…"}` (an Automerge text). A float is a number,
+// as in plain JSON; a number without a fraction written over a float stays one
+// (`store::Sticky::Floats`). A map whose only key starts with `$` is `{"$map": {…}}`, so that
 // nothing else reads as a tag.
 
 /// A map's single key that is a tag, or would be taken for one.
@@ -270,9 +270,6 @@ pub(crate) fn scalar_to_json(scalar: &ScalarValue, form: JsonForm) -> Option<Jso
                 return Some(tagged("$timestamp", form.timestamps.json(*t)));
             }
             ScalarValue::Bytes(b) => return Some(tagged("$bytes", BASE64.encode(b).into())),
-            ScalarValue::F64(f) if f.fract() == 0.0 => {
-                return Some(tagged("$float", serde_json::Number::from_f64(*f)?.into()));
-            }
             _ => {}
         }
     }
@@ -590,11 +587,6 @@ impl Val {
                 })?))
             }
             "$counter" => Val::Scalar(ScalarValue::counter(integer(value)?)),
-            "$float" => Val::Scalar(ScalarValue::F64(
-                value
-                    .as_f64()
-                    .ok_or_else(|| format!("$float: not a number: {value}"))?,
-            )),
             "$timestamp" => {
                 let text = match value {
                     JsonValue::String(text) => text.clone(),