rollup merge of #21718: alexcrichton/stabilize-from-str

This commits adds an associated type to the `FromStr` trait representing an
error payload for parses which do not succeed. The previous return value,
`Option<Self>` did not allow for this form of payload. After the associated type
was added, the following attributes were applied:

* `FromStr` is now stable
* `FromStr::Err` is now stable
* `FromStr::from_str` is now stable
* `StrExt::parse` is now stable
* `FromStr for bool` is now stable
* `FromStr for $float` is now stable
* `FromStr for $integral` is now stable
* Errors returned from stable `FromStr` implementations are stable
* Errors implement `Display` and `Error` (both impl blocks being `#[stable]`)

Closes #15138

1 files changed, 5 insertions, 4 deletions

diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index 2e7a6fd4923..b50f12deb44 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -2127,7 +2127,7 @@ macro_rules! read_primitive {
                 Json::F64(f) => Err(ExpectedError("Integer".to_string(), format!("{}", f))),
                 // re: #12967.. a type w/ numeric keys (ie HashMap<uint, V> etc)
                 // is going to have a string here, as per JSON spec.
-                Json::String(s) => match s.parse() {
+                Json::String(s) => match s.parse().ok() {
                     Some(f) => Ok(f),
                     None => Err(ExpectedError("Number".to_string(), s)),
                 },
@@ -2165,7 +2165,7 @@ impl ::Decoder for Decoder {
             Json::String(s) => {
                 // re: #12967.. a type w/ numeric keys (ie HashMap<uint, V> etc)
                 // is going to have a string here, as per JSON spec.
-                match s.parse() {
+                match s.parse().ok() {
                     Some(f) => Ok(f),
                     None => Err(ExpectedError("Number".to_string(), s)),
                 }
@@ -2597,8 +2597,9 @@ impl<'a, T: Encodable> fmt::Display for AsPrettyJson<'a, T> {
 }
 
 impl FromStr for Json {
-    fn from_str(s: &str) -> Option<Json> {
-        from_str(s).ok()
+    type Err = BuilderError;
+    fn from_str(s: &str) -> Result<Json, BuilderError> {
+        from_str(s)
     }
 }