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use std::ops::Index;
use crate::opcode::{CodeIdx, ConstantIdx, OpCode};
use crate::value::Value;
/// Represents a source location from which one or more operations
/// were compiled.
///
/// The span itself is an index into a [codemap::Codemap], and the
/// structure tracks the number of operations that were yielded from
/// the same span.
///
/// At error reporting time, it becomes possible to either just fetch
/// the textual representation of that span from the codemap, or to
/// even re-parse the AST using rnix to create more semantically
/// interesting errors.
#[derive(Clone, Debug)]
struct SourceSpan {
/// Span into the [codemap::Codemap].
span: codemap::Span,
/// Number of instructions derived from this span.
count: usize,
}
#[derive(Clone, Debug, Default)]
pub struct Chunk {
pub code: Vec<OpCode>,
pub constants: Vec<Value>,
spans: Vec<SourceSpan>,
#[cfg(feature = "disassembler")]
pub codemap: std::rc::Rc<codemap::CodeMap>,
}
impl Index<ConstantIdx> for Chunk {
type Output = Value;
fn index(&self, index: ConstantIdx) -> &Self::Output {
&self.constants[index.0]
}
}
impl Index<CodeIdx> for Chunk {
type Output = OpCode;
fn index(&self, index: CodeIdx) -> &Self::Output {
&self.code[index.0]
}
}
impl Chunk {
pub fn push_op(&mut self, data: OpCode, span: codemap::Span) -> CodeIdx {
let idx = self.code.len();
self.code.push(data);
self.push_span(span);
CodeIdx(idx)
}
pub fn push_constant(&mut self, data: Value) -> ConstantIdx {
let idx = self.constants.len();
self.constants.push(data);
ConstantIdx(idx)
}
// Span tracking implementation
fn push_span(&mut self, span: codemap::Span) {
match self.spans.last_mut() {
// We do not need to insert the same span again, as this
// instruction was compiled from the same span as the last
// one.
Some(last) if last.span == span => last.count += 1,
// In all other cases, this is a new source span.
_ => self.spans.push(SourceSpan { span, count: 1 }),
}
}
/// Retrieve the [codemap::Span] from which the instruction at
/// `offset` was compiled.
pub fn get_span(&self, offset: CodeIdx) -> codemap::Span {
let mut pos = 0;
for span in &self.spans {
pos += span.count;
if pos > offset.0 {
return span.span;
}
}
panic!("compiler error: chunk missing span for offset {}", offset.0);
}
/// Retrieve the line from which the instruction at `offset` was
/// compiled. Only available when the chunk carries a codemap,
/// i.e. when the disassembler is enabled.
#[cfg(feature = "disassembler")]
pub fn get_line(&self, offset: CodeIdx) -> usize {
let span = self.get_span(offset);
self.codemap.look_up_span(span).begin.line + 1
}
}
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