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, 2 insertions, 2 deletions

diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 493a97c24cf..2cf6058a433 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -613,7 +613,7 @@ impl<'a> StringReader<'a> {
         // find the integer representing the name
         self.scan_digits(base);
         let encoded_name : u32 = self.with_str_from(start_bpos, |s| {
-            num::from_str_radix(s, 10).unwrap_or_else(|| {
+            num::from_str_radix(s, 10).ok().unwrap_or_else(|| {
                 panic!("expected digits representing a name, got {:?}, {}, range [{:?},{:?}]",
                       s, whence, start_bpos, self.last_pos);
             })
@@ -631,7 +631,7 @@ impl<'a> StringReader<'a> {
         let start_bpos = self.last_pos;
         self.scan_digits(base);
         let encoded_ctxt : ast::SyntaxContext = self.with_str_from(start_bpos, |s| {
-            num::from_str_radix(s, 10).unwrap_or_else(|| {
+            num::from_str_radix(s, 10).ok().unwrap_or_else(|| {
                 panic!("expected digits representing a ctxt, got {:?}, {}", s, whence);
             })
         });