implement support for start function

examples/microw8/circles.cwa

@@ -5,7 +5,7 @@ import "env.sin" fn sin(f32) -> f32;
 import "env.cls" fn cls(i32);
 
 export fn tic(time: i32) {
-    cls(0);
+    cls(32);
     let i: i32;
     loop outer {
         let lazy fi = i as f32 / 4 as f32;

examples/microw8/technotunnel.cwa

@@ -1,6 +1,5 @@
 import "env.memory" memory(4);
 import "env.sin" fn sin(f32) -> f32;
-import "env.atan2" fn atan2(f32, f32) -> f32;
 
 export fn tic(time: i32) {
     let i: i32;

src/ast.rs

@@ -53,6 +53,7 @@ pub struct GlobalVar {
 pub struct Function {
     pub span: Span,
     pub export: bool,
+    pub start: bool,
     pub name: String,
     pub params: Vec<(String, Type)>,
     pub type_: Option<Type>,

src/emit.rs

@@ -3,7 +3,7 @@ use std::collections::HashMap;
 use wasm_encoder::{
     BlockType, CodeSection, DataSection, EntityType, Export, ExportSection, Function,
     FunctionSection, GlobalSection, GlobalType, ImportSection, Instruction, MemArg, MemoryType,
-    Module, TypeSection, ValType,
+    Module, StartSection, TypeSection, ValType,
 };
 
 use crate::{ast, intrinsics::Intrinsics};
@@ -94,9 +94,14 @@ pub fn emit(script: &ast::Script) -> Vec<u8> {
         let mut exports = ExportSection::new();
         let mut code = CodeSection::new();
 
+        let mut start_index = None;
+
         let intrinsics = Intrinsics::new();
 
         for func in script.functions.iter() {
+            if func.start {
+                start_index = Some(function_map.len() as u32);
+            }
             function_map.insert(func.name.clone(), function_map.len() as u32);
         }
 
@@ -118,6 +123,11 @@ pub fn emit(script: &ast::Script) -> Vec<u8> {
             module.section(&global_section);
         }
         module.section(&exports);
+
+        if let Some(function_index) = start_index {
+            module.section(&StartSection { function_index });
+        }
+
         module.section(&code);
     }
 
@@ -611,9 +621,10 @@ fn emit_expression<'a>(ctx: &mut FunctionContext<'a>, expr: &'a ast::Expression)
             ctx.labels.pop();
             ctx.function.instruction(&Instruction::End);
         }
-        ast::Expr::LabelBlock {label, block } => {
+        ast::Expr::LabelBlock { label, block } => {
             ctx.labels.push(label.to_string());
-            ctx.function.instruction(&Instruction::Block(map_block_type(block.type_)));
+            ctx.function
+                .instruction(&Instruction::Block(map_block_type(block.type_)));
             emit_expression(ctx, block);
             ctx.labels.pop();
             ctx.function.instruction(&Instruction::End);

src/parser.rs

@@ -6,11 +6,8 @@ use std::fmt;
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 enum Token {
-    Import,
-    Export,
     Fn,
     Let,
-    Memory,
     Global,
     Mut,
     Loop,
@@ -24,7 +21,6 @@ enum Token {
     If,
     Else,
     Return,
-    Data,
     Ident(String),
     Str(String),
     Int(i32),
@@ -38,11 +34,8 @@ enum Token {
 impl fmt::Display for Token {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            Token::Import => write!(f, "import"),
-            Token::Export => write!(f, "export"),
             Token::Fn => write!(f, "fn"),
             Token::Let => write!(f, "let"),
-            Token::Memory => write!(f, "memory"),
             Token::Global => write!(f, "global"),
             Token::Mut => write!(f, "mut"),
             Token::Loop => write!(f, "loop"),
@@ -56,7 +49,6 @@ impl fmt::Display for Token {
             Token::If => write!(f, "if"),
             Token::Else => write!(f, "else"),
             Token::Return => write!(f, "return"),
-            Token::Data => write!(f, "data"),
             Token::Ident(s) => write!(f, "{}", s),
             Token::Str(s) => write!(f, "{:?}", s),
             Token::Int(v) => write!(f, "{}", v),
@@ -231,11 +223,8 @@ fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = Simple<char>> {
     }
 
     let ident = ident().map(|ident: String| match ident.as_str() {
-        "import" => Token::Import,
-        "export" => Token::Export,
         "fn" => Token::Fn,
         "let" => Token::Let,
-        "memory" => Token::Memory,
         "global" => Token::Global,
         "mut" => Token::Mut,
         "loop" => Token::Loop,
@@ -249,7 +238,6 @@ fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = Simple<char>> {
         "if" => Token::If,
         "else" => Token::Else,
         "return" => Token::Return,
-        "data" => Token::Data,
         _ => Token::Ident(ident),
     });
 
@@ -755,7 +743,7 @@ fn script_parser() -> impl Parser<Token, ast::Script, Error = Simple<Token>> + C
     let expression = expression_out.unwrap();
 
     let top_level_item = {
-        let import_memory = just(Token::Memory)
+        let import_memory = just(Token::Ident("memory".to_string()))
             .ignore_then(
                 integer
                     .clone()
@@ -795,7 +783,7 @@ fn script_parser() -> impl Parser<Token, ast::Script, Error = Simple<Token>> + C
             })
             .boxed();
 
-        let import = just(Token::Import)
+        let import = just(Token::Ident("import".to_string()))
             .ignore_then(string.clone())
             .then(import_memory.or(import_global).or(import_function))
             .then_ignore(just(Token::Ctrl(';')))
@@ -814,8 +802,9 @@ fn script_parser() -> impl Parser<Token, ast::Script, Error = Simple<Token>> + C
             .then(type_parser())
             .boxed();
 
-        let function = just(Token::Export)
+        let function = just(Token::Ident("export".to_string()))
             .or_not()
+            .then(just(Token::Ident("start".to_string())).or_not())
             .then_ignore(just(Token::Fn))
             .then(identifier.clone())
             .then(
@@ -829,11 +818,12 @@ fn script_parser() -> impl Parser<Token, ast::Script, Error = Simple<Token>> + C
                     .or_not(),
             )
             .then(block.clone())
-            .map_with_span(|((((export, name), params), type_), body), span| {
+            .map_with_span(|(((((export, start), name), params), type_), body), span| {
                 ast::TopLevelItem::Function(ast::Function {
                     span,
                     params,
                     export: export.is_some(),
+                    start: start.is_some(),
                     name,
                     type_,
                     body,
@@ -875,7 +865,7 @@ fn script_parser() -> impl Parser<Token, ast::Script, Error = Simple<Token>> + C
 
         let data_string = string.map(|s| ast::DataValues::String(s));
 
-        let data = just(Token::Data)
+        let data = just(Token::Ident("data".to_string()))
             .ignore_then(expression.clone())
             .then(
                 data_i8

src/typecheck.rs

@@ -150,6 +150,36 @@ pub fn tc_script(script: &mut ast::Script, source: &str) -> Result<()> {
         }
     }
 
+    let mut start_function: Option<&ast::Function> = None;
+    for f in &script.functions {
+        if f.start {
+            if !f.params.is_empty() || f.type_.is_some() {
+                Report::build(ReportKind::Error, (), f.span.start)
+                    .with_message("Start function can't have params or a return value")
+                    .with_label(
+                        Label::new(f.span.clone())
+                            .with_message("Start function can't have params or a return value")
+                            .with_color(Color::Red),
+                    )
+                    .finish()
+                    .eprint(Source::from(source))
+                    .unwrap();
+
+                result = Err(());
+            }
+            if let Some(prev) = start_function {
+                result = report_duplicate_definition(
+                    "Start function already defined",
+                    &f.span,
+                    &prev.span,
+                    source,
+                );
+            } else {
+                start_function = Some(f);
+            }
+        }
+    }
+
     for data in &mut script.data {
         tc_const(&mut data.offset, source)?;
         if data.offset.type_ != Some(I32) {