feat(tazjin/rlox): Bootstrap rough shape of bytecode compiler r/2237

This one necessarily has to diverge more from the book than the
treewalk interpreter did, so some of this is expected to change, but
I'm happy with the rough shape.

Since we're reusing the old scanner, the compiler/parser struct owns
an iterator over all tokens with which the pull-scanner from the
bytecode chapters is simulated.

Change-Id: Icfa0bd4729d9df786e08f7e49a25cba1b9989a91
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2556
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

1 files changed, 84 insertions, 0 deletions

diff --git a/users/tazjin/rlox/src/bytecode/compiler.rs b/users/tazjin/rlox/src/bytecode/compiler.rs
new file mode 100644
index 000000000000..0197885a52d2
--- /dev/null
+++ b/users/tazjin/rlox/src/bytecode/compiler.rs
@@ -0,0 +1,84 @@
+use super::chunk::Chunk;
+use super::errors::{Error, ErrorKind, LoxResult};
+use super::opcode::OpCode;
+use crate::scanner;
+
+struct Compiler<T: Iterator<Item = scanner::Token>> {
+    // panic: bool,
+    errors: Vec<Error>,
+    tokens: T,
+    chunk: Chunk,
+
+    // TODO(tazjin): Restructure so that these don't need to be Option?
+    current: Option<scanner::Token>,
+    previous: Option<scanner::Token>,
+}
+
+impl<T: Iterator<Item = scanner::Token>> Compiler<T> {
+    fn compile(&mut self) -> LoxResult<()> {
+        self.advance();
+        self.expression();
+        self.consume(
+            &scanner::TokenKind::Eof,
+            ErrorKind::ExpectedToken("Expected end of expression"),
+        )?;
+
+        self.end_compiler()
+    }
+
+    fn advance(&mut self) {
+        self.previous = self.current.take();
+        self.current = self.tokens.next();
+    }
+
+    fn expression(&mut self) {
+        unimplemented!()
+    }
+
+    fn consume(
+        &mut self,
+        expected: &scanner::TokenKind,
+        err: ErrorKind,
+    ) -> LoxResult<()> {
+        unimplemented!()
+    }
+
+    fn current_chunk(&mut self) -> &mut Chunk {
+        &mut self.chunk
+    }
+
+    fn end_compiler(&mut self) -> LoxResult<()> {
+        let line = self.previous().line;
+        self.current_chunk().add_op(OpCode::OpReturn, line);
+        Ok(())
+    }
+
+    fn previous(&self) -> &scanner::Token {
+        self.previous
+            .as_ref()
+            .expect("invalid internal compiler state: missing previous token")
+    }
+}
+
+pub fn compile(code: &str) -> Result<Chunk, Vec<Error>> {
+    let chars = code.chars().collect::<Vec<char>>();
+    let tokens = scanner::scan(&chars).map_err(|errors| {
+        errors.into_iter().map(Into::into).collect::<Vec<Error>>()
+    })?;
+
+    let mut compiler = Compiler {
+        tokens: tokens.into_iter().peekable(),
+        errors: vec![],
+        current: None,
+        previous: None,
+        chunk: Default::default(),
+    };
+
+    compiler.compile()?;
+
+    if compiler.errors.is_empty() {
+        Ok(unimplemented!())
+    } else {
+        Err(compiler.errors)
+    }
+}