measureme 12.0.3

Support crate for rustc's self-profiling feature
Documentation 
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use smallvec::SmallVec;

use crate::{Profiler, StringComponent, StringId};

/// Event IDs are strings conforming to the following grammar:
///
/// ```ignore
///   <event_id> = <label> {<argument>}
///   <label> = <text>
///   <argument> = '\x1E' <text>
///   <text> = regex([[[:^cntrl:]][[:space:]]]+) // Anything but ASCII control characters except for whitespace.
///  ```
///
/// This means there's always a "label", followed by an optional list of
/// arguments. Future versions may support other optional suffixes (with a tag
/// other than '\x11' after the '\x1E' separator), such as a "category".

/// The byte used to separate arguments from the label and each other.
pub const SEPARATOR_BYTE: &str = "\x1E";

/// An `EventId` is a `StringId` with the additional guarantee that the
/// corresponding string conforms to the event_id grammar.
#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug)]
#[repr(C)]
pub struct EventId(StringId);

impl EventId {
    pub const INVALID: EventId = EventId(StringId::INVALID);

    #[inline]
    pub fn to_string_id(self) -> StringId {
        self.0
    }

    #[inline]
    pub fn as_u64(self) -> u64 {
        self.0.as_u64()
    }

    #[inline]
    pub fn from_label(label: StringId) -> Self {
        EventId(label)
    }

    #[inline]
    pub fn from_virtual(virtual_id: StringId) -> Self {
        EventId(virtual_id)
    }

    /// Create an EventId from a raw u64 value. Only used internally for
    /// deserialization.
    #[inline]
    pub fn from_u64(raw_id: u64) -> Self {
        EventId(StringId::new(raw_id))
    }
}

pub struct EventIdBuilder<'p> {
    profiler: &'p Profiler,
}

impl<'p> EventIdBuilder<'p> {
    pub fn new(profiler: &Profiler) -> EventIdBuilder<'_> {
        EventIdBuilder { profiler }
    }

    #[inline]
    pub fn from_label(&self, label: StringId) -> EventId {
        // Just forward the string ID, a single identifier is a valid event_id
        EventId::from_label(label)
    }

    pub fn from_label_and_arg(&self, label: StringId, arg: StringId) -> EventId {
        EventId(self.profiler.alloc_string(&[
            // Label
            StringComponent::Ref(label),
            // Seperator and start tag for arg
            StringComponent::Value(SEPARATOR_BYTE),
            // Arg string id
            StringComponent::Ref(arg),
        ]))
    }

    pub fn from_label_and_args(&self, label: StringId, args: &[StringId]) -> EventId {
        // Store up to 7 components on the stack: 1 label + 3 arguments + 3 argument separators
        let mut parts = SmallVec::<[StringComponent<'_>; 7]>::with_capacity(1 + args.len() * 2);

        parts.push(StringComponent::Ref(label));

        for arg in args {
            parts.push(StringComponent::Value(SEPARATOR_BYTE));
            parts.push(StringComponent::Ref(*arg));
        }

        EventId(self.profiler.alloc_string(&parts[..]))
    }
}