Use static strings for CustomError.

This resulted in a 20% speedup.

scripts/callgrind.bash

@@ -4,10 +4,23 @@ set -euo pipefail
 IFS=$'\n\t'
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
+: ${PROFILE:="perf"}
 
+function main {
+    local additional_flags=()
+    if [ "$PROFILE" = "dev" ] || [ "$PROFILE" = "debug" ]; then
+        PROFILE="debug"
+    else
+        additional_flags+=(--profile "$PROFILE")
+        # We have to disable avx512 because valgrind does not yet support it.
+        export RUSTFLAGS="-C target-feature=-avx512"
+    fi
 
-(cd "$DIR/../" && RUSTFLAGS="-C opt-level=0" cargo build --no-default-features)
-valgrind --tool=callgrind --callgrind-out-file="$DIR/../callgrind.out" "$DIR/../target/debug/parse" "${@}"
+    (cd "$DIR/../" && RUSTFLAGS="-C target-cpu=x86-64-v3" cargo build --no-default-features "${additional_flags[@]}")
+    valgrind --tool=callgrind --callgrind-out-file="$DIR/../callgrind.out" "$DIR/../target/${PROFILE}/parse" "${@}"
 
     echo "You probably want to run:"
     echo "callgrind_annotate --auto=yes '$DIR/../callgrind.out'"
+}
+
+main "${@}"

src/error/error.rs

@@ -4,10 +4,9 @@ use nom::IResult;
 
 pub(crate) type Res<T, U> = IResult<T, U, CustomError<T>>;
 
-// TODO: MyError probably shouldn't be based on the same type as the input type since it's used exclusively with static strings right now.
 #[derive(Debug)]
 pub enum CustomError<I> {
-    MyError(MyError<I>),
+    MyError(MyError<&'static str>),
     Nom(I, ErrorKind),
     IO(std::io::Error),
 }
@@ -31,3 +30,9 @@ impl<I> From<std::io::Error> for CustomError<I> {
         CustomError::IO(value)
     }
 }
+
+impl<I> From<&'static str> for CustomError<I> {
+    fn from(value: &'static str) -> Self {
+        CustomError::MyError(MyError(value))
+    }
+}

src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(round_char_boundary)]
 #![feature(exit_status_error)]
 #![feature(trait_alias)]
 // TODO: #![warn(missing_docs)]