refactor(lexer, ast): Rewrite decl with c standard grammar of decl

src/ast/parser/decl.rs

@@ -1,7 +1,8 @@
 use crate::{
     ast::err::ParseError,
     ast::types::{
-        ArrayDimension, CompileUnit, FuncDeclStmt, GlobalDeclStmt, Param, VarDeclStmt, VarDeclStmtValue,
+        ArrayDimension, CompileUnit, Expr, FuncDeclStmt, GlobalDeclStmt, Param, VarDeclStmt,
+        VarDeclStmtValue,
     },
     diagnostic::span::Span,
     lexer::types::{TokenValue, TypeIdent},
@@ -9,11 +10,41 @@ use crate::{
 
 use super::{ParseProcessError, ParseType, Parser};
 
+#[derive(Clone, Copy)]
+enum StorageClass {
+    Static,
+}
+
+struct DeclSpecifiers {
+    _storage_class: Option<StorageClass>,
+    type_specifier: TypeIdent,
+    type_span: Span,
+}
+
+struct Declarator {
+    name: String,
+    name_span: Span,
+    suffixes: Vec<DeclaratorSuffix>,
+}
+
+enum DeclaratorSuffix {
+    Array(ArrayDimension),
+    Function {
+        params: Vec<Param>,
+        span: Span,
+    },
+}
+
+struct InitDeclarator {
+    declarator: Declarator,
+    initializer: Option<Expr>,
+}
+
 impl Parser {
     pub(super) fn parse_compile_unit(&mut self) -> CompileUnit {
         let mut global_decls = vec![];
         while !self.is_eof() {
-            if let Some(decl) = self.parse_global_decl_stmt() {
+            if let Some(decl) = self.parse_external_decl_stmt() {
                 global_decls.push(decl);
             } else {
                 self.until_next_token(&[TokenValue::Semicolon, TokenValue::RBrace]);
@@ -22,260 +53,391 @@ impl Parser {
         CompileUnit { global_decls }
     }
 
-    fn parse_global_decl_stmt(&mut self) -> Option<GlobalDeclStmt> {
-        match self.parse_func_decl_stmt() {
-            Ok(func_decl) => return Some(GlobalDeclStmt::FuncDecl(func_decl)),
-            Err(ParseProcessError::ErrorInMatch) => {
-                return None
-            },
-            _ => {}
+    fn parse_external_decl_stmt(&mut self) -> Option<GlobalDeclStmt> {
+        let specifiers = match self.parse_decl_specifiers(ParseType::MustParse) {
+            Ok(specifiers) => specifiers,
+            Err(ParseProcessError::ErrorInMatch) => return None,
+            Err(ParseProcessError::TryNext) => unreachable!(),
         };
-        match self.parse_var_decl_stmt(ParseType::MustParse) {
-            Ok(var_decl) => return Some(GlobalDeclStmt::VarDecl(var_decl)),
-            Err(ParseProcessError::ErrorInMatch) => {
-                return None
-            },
-            _ => {}
-        }
-        let token = self.next().clone();
-        self.diagnostics.add_from_frontend_error(
-            ParseError::ExpectedBefore(token.value, "ident"),
-            token.span,
-        );
-        None
-    }
-    // fn until_next_stmt(&mut self) {
-    //     // skip tokens until we find a semicolon or a right brace, which may indicate the end of the declaration
-    //     while let Some(t) = self.peek() {
-    //         if matches!(t.value, TokenValue::Semicolon | TokenValue::RBrace) {
-    //             self.advance(1);
-    //             break;
-    //         }
-    //         self.advance(1);
-    //     }
-    // }
-    fn parse_type_and_name(&mut self, parse_type: ParseType) -> Result<(TypeIdent, String, Span, Span), ParseProcessError> {
-        let type_token = self.peek().clone();
-        let type_ident = match self.peek().value.as_type_ident() {
-            Some(ti) => ti,
-            None => {
-                if matches!(parse_type, ParseType::MustParse) {
-                    let token = self.next().clone();
-                    self.diagnostics.add_from_frontend_error(
-                        ParseError::ExpectedBefore(token.value, "type ident"),
-                        token.span,
-                    );
-                    return Err(ParseProcessError::ErrorInMatch);
-                }
-                return Err(ParseProcessError::TryNext);
-            },
+        let declarator = match self.parse_declarator() {
+            Ok(declarator) => declarator,
+            Err(ParseProcessError::ErrorInMatch) => return None,
+            Err(ParseProcessError::TryNext) => unreachable!(),
         };
-        let type_span = type_token.span;
-        self.advance(1);
-        let name = match self.peek().value.as_ident() {
-            None => {
-                let next_span = self.peek().span;
-                self.diagnostics.add_from_frontend_error(
-                    ParseError::ExpectedIdentAfter(type_token.value),
-                    next_span
-                );
-                return Err(ParseProcessError::ErrorInMatch);
-            }
-            Some(ident) => ident,
-        };
-        let name_span = self.peek().span;
-        self.advance(1);
-        Ok((type_ident, name, type_span, name_span))
-    }
-    fn parse_func_decl_stmt(&mut self) -> Result<FuncDeclStmt, ParseProcessError> {
-        let (return_type, name, ret_type_span, name_span) = self.parse_type_and_name(ParseType::MustParse)?;
-        if matches!(self.peek().value, TokenValue::LParen) {
-        } else {
-            self.back(2);
-            return Err(ParseProcessError::TryNext);
-        }
-        // from here we can be sure it's a function declaration, so we can report error if the syntax is wrong
-        let params = self.parse_param_list()?;
-        let body = self.parse_block_stmt(ParseType::MustParse)?;
-        Ok(FuncDeclStmt {
-            return_type: return_type.into(),
-            name,
-            params,
-            body,
-            ret_type_span,
-            name_span,
-        })
-    }
-    fn parse_param_list(&mut self) -> Result<Vec<Param>, ParseProcessError> {
-        if self.peek().value != TokenValue::LParen {
-            let token = self.next().clone();
-            self.diagnostics.add_from_frontend_error(
-                ParseError::ExpectedBefore(token.value, "`(`"),
-                token.span,
-            );
-            return Err(ParseProcessError::ErrorInMatch);
-        }
-        self.advance(1);
-        let mut params = vec![];
-        let mut last_is_var = false;
-        while !self.is_eof() {
-            if self.peek().value == TokenValue::RParen {
-                self.advance(1);
-                break;
-            }
-            if last_is_var {
-                self.must_match_token(&TokenValue::Comma, "`,` or `)`")
-                    .inspect_err(|_| self.until_next_token(&[TokenValue::RBrace]))?;                
-            }
-            match self.parse_param() {
-                Ok(param) => {
-                    params.push(param);
-                    last_is_var = true;
-                }
-                Err(_e) => {
-                    self.until_next_token(&[TokenValue::RParen]);
-                    if self.last().value == TokenValue::RParen {
-                        break;
-                    }
-                }
+
+        if self.peek().value == TokenValue::LBrace {
+            match self.finish_func_def_stmt(specifiers, declarator) {
+                Ok(func_decl) => return Some(GlobalDeclStmt::FuncDecl(func_decl)),
+                Err(ParseProcessError::ErrorInMatch) => return None,
+                Err(ParseProcessError::TryNext) => unreachable!(),
             }
         }
-        Ok(params)
-    }
-    fn parse_param(&mut self) -> Result<Param, ParseProcessError> {
-        let (param_type, name, type_span, name_span) = self.parse_type_and_name(ParseType::MustParse)?;
-        Ok(Param {
-            param_type: param_type.into(),
-            name,
-            dimensions: self.parse_array_dimensions(true)?,
-            name_span,
-            type_span,
-        })
-    }
-    // fn must_match_semicolon(&mut self) -> Option<()> {
-    //     if self
-    //         .peek()
-    //         .is_some_and(|t| matches!(t.value, TokenValue::Semicolon))
-    //     {
-    //         self.advance(1);
-    //         Some(())
-    //     } else {
-    //         let token = self.next().clone();
-    //         self.diagnostics
-    //             .add_from_frontend_error(ParseError::ExpectedBefore(token.value, "`;`"), token.span);
-    //         while let Some(t) = self.peek() {
-    //             if matches!(t.value, TokenValue::Semicolon) {
-    //                 self.advance(1);
-    //                 break;
-    //             }
-    //             if matches!(t.value, TokenValue::RBrace) {
-    //                 break;
-    //             }
-    //             self.advance(1);
-    //         }
-    //         None
-    //     }
-    // }
-    pub(super) fn parse_var_decl_stmt(&mut self, parse_type: ParseType) -> Result<VarDeclStmt, ParseProcessError> {
-        self.parse_var_decl_stmt_inner(parse_type, true)
+
+        match self.finish_var_decl_stmt(specifiers, declarator, true, true) {
+            Ok(var_decl) => Some(GlobalDeclStmt::VarDecl(var_decl)),
+            Err(ParseProcessError::ErrorInMatch) => None,
+            Err(ParseProcessError::TryNext) => unreachable!(),
+        }
     }
 
-    pub(super) fn parse_var_decl_stmt_inner(&mut self, parse_type: ParseType, consume_semicolon: bool) -> Result<VarDeclStmt, ParseProcessError> {
-        let mut values = vec![];
-        let (var_type, name, type_span, name_span) = match self.parse_type_and_name(parse_type) {
-            Ok(res) => res,
-            Err(_e) => {
-                if matches!(parse_type, ParseType::TryParse) {
-                    return Err(ParseProcessError::TryNext);
-                } else {
-                    return Err(ParseProcessError::ErrorInMatch);
-                }
-            }
-        };
-        let dimensions = self.parse_array_dimensions(false)?;
-        let value = if self.peek().value == TokenValue::Equal {
+    fn parse_decl_specifiers(
+        &mut self,
+        parse_type: ParseType,
+    ) -> Result<DeclSpecifiers, ParseProcessError> {
+        let storage_class = if self.peek().value == TokenValue::Static {
             self.advance(1);
-            Some(self.parse_expr()?)
+            Some(StorageClass::Static)
         } else {
             None
         };
-        values.push(VarDeclStmtValue { name, name_span, dimensions, value });
-        let mut last_name = true; // indicate whether the last parsed token is a variable name
-        while !self.is_eof() {
-            if matches!(self.peek().value, TokenValue::Semicolon) { // statement end
-                break;
+
+        let type_token = self.peek().clone();
+        let type_specifier = match type_token.value.as_type_ident() {
+            Some(type_specifier) => {
+                self.advance(1);
+                type_specifier
             }
-            if last_name { // expect a comma after a variable name
-                self.must_match_token(&TokenValue::Comma, "`,` or `;`")?;
-                last_name = false;
+            None if parse_type == ParseType::TryParse && storage_class.is_none() => {
+                return Err(ParseProcessError::TryNext);
             }
-            if let Some(ident) = self.peek().value.as_ident() {
-                let span = self.next().span;
-                let dimensions = self.parse_array_dimensions(false)?;
-                let value = if self.peek().value == TokenValue::Equal {
-                    self.advance(1);
-                    Some(self.parse_expr()?)
-                } else {
-                    None
-                };
-                values.push(VarDeclStmtValue { name: ident, name_span: span, dimensions, value });
-                last_name = true;
-            } else {
-                let token = self.next().clone();
+            None => {
+                let token = self.next();
                 self.diagnostics.add_from_frontend_error(
-                    ParseError::ExpectedIdentAfter(TokenValue::TypeIdent(var_type)),
+                    ParseError::ExpectedBefore(token.value, "type specifier"),
                     token.span,
                 );
                 return Err(ParseProcessError::ErrorInMatch);
             }
+        };
+
+        Ok(DeclSpecifiers {
+            _storage_class: storage_class,
+            type_specifier,
+            type_span: type_token.span,
+        })
+    }
+
+    fn parse_declarator(&mut self) -> Result<Declarator, ParseProcessError> {
+        self.parse_direct_declarator()
+    }
+
+    fn parse_direct_declarator(&mut self) -> Result<Declarator, ParseProcessError> {
+        let mut declarator = match self.peek().value.clone() {
+            TokenValue::Ident(name) => {
+                let name_span = self.peek().span;
+                self.advance(1);
+                Declarator {
+                    name,
+                    name_span,
+                    suffixes: vec![],
+                }
+            }
+            TokenValue::LParen => {
+                self.advance(1);
+                let declarator = self.parse_declarator()?;
+                self.must_match_token(&TokenValue::RParen, "`)`")?;
+                declarator
+            }
+            _ => {
+                let token = self.next();
+                self.diagnostics.add_from_frontend_error(
+                    ParseError::ExpectedBefore(token.value, "declarator"),
+                    token.span,
+                );
+                return Err(ParseProcessError::ErrorInMatch);
+            }
+        };
+
+        loop {
+            match self.peek().value {
+                TokenValue::LBracket => {
+                    let dimension = self.parse_array_declarator_suffix()?;
+                    declarator.suffixes.push(DeclaratorSuffix::Array(dimension));
+                }
+                TokenValue::LParen => {
+                    let start_span = self.next().span;
+                    let params = self.parse_parameter_list_after_lparen()?;
+                    let end_span = self.last().span;
+                    declarator.suffixes.push(DeclaratorSuffix::Function {
+                        params,
+                        span: Span::from_two(start_span, end_span),
+                    });
+                }
+                _ => break,
+            }
         }
+
+        Ok(declarator)
+    }
+
+    fn parse_array_declarator_suffix(&mut self) -> Result<ArrayDimension, ParseProcessError> {
+        let start_span = self.next().span;
+        let value = if self.peek().value == TokenValue::RBracket {
+            None
+        } else {
+            Some(self.parse_expr()?)
+        };
+        let end_span = match &self.peek().value {
+            TokenValue::RBracket => {
+                let span = self.peek().span;
+                self.advance(1);
+                span
+            }
+            TokenValue::Eof => {
+                self.diagnostics.add_from_frontend_error(
+                    ParseError::ExpectedBefore(TokenValue::Eof, "`]`"),
+                    start_span,
+                );
+                return Err(ParseProcessError::ErrorInMatch);
+            }
+            _ => {
+                let token = self.next();
+                self.diagnostics.add_from_frontend_error(
+                    ParseError::ExpectedBefore(token.value, "`]`"),
+                    token.span,
+                );
+                return Err(ParseProcessError::ErrorInMatch);
+            }
+        };
+        Ok(ArrayDimension {
+            value,
+            span: Span::from_two(start_span, end_span),
+        })
+    }
+
+    fn parse_parameter_list_after_lparen(&mut self) -> Result<Vec<Param>, ParseProcessError> {
+        if self.peek().value == TokenValue::RParen {
+            self.advance(1);
+            return Ok(vec![]);
+        }
+
+        let mut params = vec![];
+        loop {
+            match self.parse_param() {
+                Ok(param) => params.push(param),
+                Err(error) => {
+                    self.until_next_token(&[TokenValue::Comma, TokenValue::RParen]);
+                    if self.last().value == TokenValue::RParen {
+                        return Err(error);
+                    }
+                    continue;
+                }
+            }
+
+            match self.peek().value {
+                TokenValue::Comma => {
+                    self.advance(1);
+                }
+                TokenValue::RParen => {
+                    self.advance(1);
+                    break;
+                }
+                _ => {
+                    self.must_match_token(&TokenValue::RParen, "`,` or `)`")?;
+                    break;
+                }
+            }
+        }
+
+        Ok(params)
+    }
+
+    fn parse_param(&mut self) -> Result<Param, ParseProcessError> {
+        let specifiers = self.parse_decl_specifiers(ParseType::MustParse)?;
+        let declarator = self.parse_declarator()?;
+        self.declarator_to_param(specifiers, declarator)
+    }
+
+    pub(super) fn parse_var_decl_stmt(
+        &mut self,
+        parse_type: ParseType,
+    ) -> Result<VarDeclStmt, ParseProcessError> {
+        self.parse_var_decl_stmt_inner(parse_type, true)
+    }
+
+    pub(super) fn parse_var_decl_stmt_inner(
+        &mut self,
+        parse_type: ParseType,
+        consume_semicolon: bool,
+    ) -> Result<VarDeclStmt, ParseProcessError> {
+        let specifiers = self.parse_decl_specifiers(parse_type)?;
+        let declarator = self.parse_declarator()?;
+        self.finish_var_decl_stmt(specifiers, declarator, consume_semicolon, false)
+    }
+
+    fn finish_func_def_stmt(
+        &mut self,
+        specifiers: DeclSpecifiers,
+        declarator: Declarator,
+    ) -> Result<FuncDeclStmt, ParseProcessError> {
+        let Declarator {
+            name,
+            name_span,
+            suffixes,
+        } = declarator;
+        let params = self.take_function_params(name_span, suffixes)?;
+        let body = self.parse_block_stmt(ParseType::MustParse)?;
+        Ok(FuncDeclStmt {
+            return_type: specifiers.type_specifier.into(),
+            name,
+            params,
+            body,
+            ret_type_span: specifiers.type_span,
+            name_span,
+        })
+    }
+
+    fn finish_var_decl_stmt(
+        &mut self,
+        specifiers: DeclSpecifiers,
+        first_declarator: Declarator,
+        consume_semicolon: bool,
+        allow_empty_declarator_list: bool,
+    ) -> Result<VarDeclStmt, ParseProcessError> {
+        let mut values = vec![];
+
+        if self.peek().value == TokenValue::Semicolon && allow_empty_declarator_list {
+            if consume_semicolon {
+                self.advance(1);
+            }
+            return Ok(VarDeclStmt {
+                values,
+                type_span: specifiers.type_span,
+                data_type: specifiers.type_specifier.into(),
+            });
+        }
+
+        let initializer = self.parse_initializer()?;
+        values.push(self.init_declarator_to_var_value(InitDeclarator {
+            declarator: first_declarator,
+            initializer,
+        })?);
+
+        while self.peek().value == TokenValue::Comma {
+            self.advance(1);
+            let declarator = self.parse_declarator()?;
+            let initializer = self.parse_initializer()?;
+            values.push(self.init_declarator_to_var_value(InitDeclarator {
+                declarator,
+                initializer,
+            })?);
+        }
+
         if consume_semicolon {
             self.must_match_token(&TokenValue::Semicolon, "`;`")?;
         }
-        Ok(VarDeclStmt { values, type_span, data_type: var_type.into()  })
+
+        Ok(VarDeclStmt {
+            values,
+            type_span: specifiers.type_span,
+            data_type: specifiers.type_specifier.into(),
+        })
     }
 
-    fn parse_array_dimensions(&mut self, allow_empty_first: bool) -> Result<Vec<ArrayDimension>, ParseProcessError> {
+    fn parse_initializer(&mut self) -> Result<Option<Expr>, ParseProcessError> {
+        if self.peek().value != TokenValue::Equal {
+            return Ok(None);
+        }
+        self.advance(1);
+        Ok(Some(self.parse_expr()?))
+    }
+
+    fn init_declarator_to_var_value(
+        &mut self,
+        init_declarator: InitDeclarator,
+    ) -> Result<VarDeclStmtValue, ParseProcessError> {
+        let Declarator {
+            name,
+            name_span,
+            suffixes,
+        } = init_declarator.declarator;
+        let dimensions = self.take_array_dimensions(suffixes)?;
+        Ok(VarDeclStmtValue {
+            name,
+            name_span,
+            dimensions,
+            value: init_declarator.initializer,
+        })
+    }
+
+    fn declarator_to_param(
+        &mut self,
+        specifiers: DeclSpecifiers,
+        declarator: Declarator,
+    ) -> Result<Param, ParseProcessError> {
+        let Declarator {
+            name,
+            name_span,
+            suffixes,
+        } = declarator;
+        let dimensions = self.take_array_dimensions(suffixes)?;
+        Ok(Param {
+            param_type: specifiers.type_specifier.into(),
+            name,
+            dimensions,
+            name_span,
+            type_span: specifiers.type_span,
+        })
+    }
+
+    fn take_array_dimensions(
+        &mut self,
+        suffixes: Vec<DeclaratorSuffix>,
+    ) -> Result<Vec<ArrayDimension>, ParseProcessError> {
         let mut dimensions = vec![];
-        while self.peek().value == TokenValue::LBracket {
-            let start_span = self.next().span;
-            let value = if self.peek().value == TokenValue::RBracket {
-                if !allow_empty_first || !dimensions.is_empty() {
-                    let span = self.peek().span;
+        for suffix in suffixes {
+            match suffix {
+                DeclaratorSuffix::Array(dimension) => dimensions.push(dimension),
+                DeclaratorSuffix::Function { span, .. } => {
                     self.diagnostics.add_from_frontend_error(
-                        ParseError::ExpectedBefore(TokenValue::RBracket, "array dimension expression"),
+                        ParseError::ExpectedBefore(TokenValue::LParen, "variable declarator"),
                         span,
                     );
                     return Err(ParseProcessError::ErrorInMatch);
                 }
-                None
-            } else {
-                Some(self.parse_expr()?)
-            };
-            let end_span = match &self.peek().value {
-                TokenValue::RBracket => {
-                    let span = self.peek().span;
-                    self.advance(1);
-                    span
-                }
-                TokenValue::Eof => {
-                    self.diagnostics.add_from_frontend_error(ParseError::ExpectedBefore(TokenValue::Eof, "`]`"), start_span);
-                    return Err(ParseProcessError::ErrorInMatch);
-                }
-                _ => {
-                    let token = self.next();
-                    self.diagnostics.add_from_frontend_error(
-                        ParseError::ExpectedBefore(token.value, "`]`"),
-                        token.span,
-                    );
-                    return Err(ParseProcessError::ErrorInMatch);
-                }
-            };
-            dimensions.push(ArrayDimension {
-                value,
-                span: Span::from_two(start_span, end_span),
-            });
+            }
         }
         Ok(dimensions)
     }
+
+    fn take_function_params(
+        &mut self,
+        name_span: Span,
+        suffixes: Vec<DeclaratorSuffix>,
+    ) -> Result<Vec<Param>, ParseProcessError> {
+        let mut params = None;
+        for suffix in suffixes {
+            match suffix {
+                DeclaratorSuffix::Function {
+                    params: suffix_params,
+                    ..
+                } if params.is_none() => params = Some(suffix_params),
+                DeclaratorSuffix::Function { span, .. } => {
+                    self.diagnostics.add_from_frontend_error(
+                        ParseError::ExpectedBefore(TokenValue::LParen, "function body"),
+                        span,
+                    );
+                    return Err(ParseProcessError::ErrorInMatch);
+                }
+                DeclaratorSuffix::Array(dimension) => {
+                    self.diagnostics.add_from_frontend_error(
+                        ParseError::ExpectedBefore(TokenValue::LBracket, "function declarator"),
+                        dimension.span,
+                    );
+                    return Err(ParseProcessError::ErrorInMatch);
+                }
+            }
+        }
+
+        match params {
+            Some(params) => Ok(params),
+            None => {
+                self.diagnostics.add_from_frontend_error(
+                    ParseError::ExpectedBefore(TokenValue::LBrace, "function declarator"),
+                    name_span,
+                );
+                Err(ParseProcessError::ErrorInMatch)
+            }
+        }
+    }
 }