Add return-type checking and fix string literal type-info bug.

dmc-lib/src/ast/expression_statement.rs

@@ -3,7 +3,10 @@ use crate::ast::ir_builder::IrBuilder;
 use crate::diagnostic::Diagnostic;
 use crate::ir::ir_return::IrReturn;
 use crate::ir::ir_statement::IrStatement;
+use crate::symbol::FunctionSymbol;
 use crate::symbol_table::SymbolTable;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 pub struct ExpressionStatement {
     expression: Box<Expression>,
@@ -31,8 +34,30 @@ impl ExpressionStatement {
         self.expression.check_name_usages(symbol_table)
     }
 
-    pub fn type_check(&mut self, symbol_table: &SymbolTable) -> Result<(), Vec<Diagnostic>> {
-        self.expression.type_check(symbol_table)
+    pub fn type_check(
+        &mut self,
+        symbol_table: &SymbolTable,
+        is_last: bool,
+        function_symbol: &Rc<RefCell<FunctionSymbol>>,
+    ) -> Result<(), Vec<Diagnostic>> {
+        self.expression.type_check(symbol_table)?;
+
+        if is_last {
+            let expression_type = self.expression.type_info();
+            let borrowed_symbol = function_symbol.borrow();
+            let return_type = borrowed_symbol.return_type_info();
+            if !return_type.is_assignable_from(expression_type) {
+                return Err(vec![Diagnostic::new(
+                    &format!(
+                        "Incompatible type on return expression: expected {} but found {}",
+                        return_type, expression_type
+                    ),
+                    self.expression.source_range().start(),
+                    self.expression.source_range().end(),
+                )]);
+            }
+        }
+        Ok(())
     }
 
     pub fn to_ir(

dmc-lib/src/ast/function.rs

@@ -168,12 +168,19 @@ impl Function {
                 .collect(),
         );
 
+        let function_symbol = self.function_symbol.as_ref().unwrap();
+        let statements_len = self.statements.len();
+
         // statements
         diagnostics.append(
             &mut self
                 .statements
                 .iter_mut()
-                .map(|statement| statement.type_check(symbol_table))
+                .enumerate()
+                .map(|(i, statement)| {
+                    let is_last = i == statements_len - 1;
+                    statement.type_check(symbol_table, is_last, function_symbol)
+                })
                 .filter_map(Result::err)
                 .flatten()
                 .collect(),

dmc-lib/src/ast/statement.rs

@@ -2,7 +2,10 @@ use crate::ast::expression_statement::ExpressionStatement;
 use crate::ast::ir_builder::IrBuilder;
 use crate::ast::let_statement::LetStatement;
 use crate::diagnostic::Diagnostic;
+use crate::symbol::FunctionSymbol;
 use crate::symbol_table::SymbolTable;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 pub enum Statement {
     Let(LetStatement),
@@ -31,11 +34,16 @@ impl Statement {
         }
     }
 
-    pub fn type_check(&mut self, symbol_table: &SymbolTable) -> Result<(), Vec<Diagnostic>> {
+    pub fn type_check(
+        &mut self,
+        symbol_table: &SymbolTable,
+        is_last: bool,
+        function_symbol: &Rc<RefCell<FunctionSymbol>>,
+    ) -> Result<(), Vec<Diagnostic>> {
         match self {
             Statement::Let(let_statement) => let_statement.type_check(symbol_table),
             Statement::Expression(expression_statement) => {
-                expression_statement.type_check(symbol_table)
+                expression_statement.type_check(symbol_table, is_last, function_symbol)
             }
         }
     }

dmc-lib/src/ast/string_literal.rs

@@ -9,7 +9,7 @@ pub struct StringLiteral {
 
 impl StringLiteral {
     pub fn new(content: &str, source_range: SourceRange) -> Self {
-        const TYPE_INFO: TypeInfo = TypeInfo::Integer;
+        const TYPE_INFO: TypeInfo = TypeInfo::String;
         Self {
             content: content.into(),
             source_range,

dmc-lib/src/type_info.rs

@@ -68,9 +68,15 @@ impl TypeInfo {
         }
     }
 
-    pub fn add_result(&self, _rhs: &Self) -> TypeInfo {
+    pub fn add_result(&self, rhs: &Self) -> TypeInfo {
         match self {
-            TypeInfo::Integer => TypeInfo::Integer,
+            TypeInfo::Integer => match rhs {
+                TypeInfo::Integer => TypeInfo::Integer,
+                TypeInfo::String => TypeInfo::String,
+                _ => panic!(
+                    "Adding things other than integers/strings to integer not yet supported."
+                ),
+            },
             TypeInfo::String => TypeInfo::String,
             _ => panic!("Adding things other than integers and strings not yet supported"),
         }

e2e-tests/src/lib.rs

@@ -137,3 +137,47 @@ mod e2e_tests {
         assert_result("fn sub() -> Int 3 - 2 end", "sub", &vec![], Value::Int(1))
     }
 }
+
+#[cfg(test)]
+mod diagnostic_tests {
+    use dmc_lib::diagnostic::Diagnostic;
+    use dmc_lib::parser::parse_compilation_unit;
+    use dmc_lib::symbol_table::SymbolTable;
+
+    fn get_diagnostics(input: &str) -> Vec<Diagnostic> {
+        let parse_result = parse_compilation_unit(input);
+        let mut compilation_unit = match parse_result {
+            Ok(compilation_unit) => compilation_unit,
+            Err(diagnostics) => {
+                return diagnostics;
+            }
+        };
+
+        let mut symbol_table = SymbolTable::new();
+
+        match compilation_unit.gather_declared_names(&mut symbol_table) {
+            Ok(_) => {}
+            Err(diagnostics) => {
+                return diagnostics;
+            }
+        }
+
+        match compilation_unit.check_name_usages(&symbol_table) {
+            Ok(_) => {}
+            Err(diagnostics) => {
+                return diagnostics;
+            }
+        }
+
+        match compilation_unit.type_check(&symbol_table) {
+            Ok(_) => vec![],
+            Err(diagnostics) => diagnostics,
+        }
+    }
+
+    #[test]
+    fn wrong_return_type() {
+        let diagnostics = get_diagnostics("fn main() -> String 42 end");
+        assert_eq!(diagnostics.len(), 1);
+    }
+}