chore: Instantiate pre_linter context with Default

As a consequence, `Position` now implements `Default`,
which results to `Position::start` (1,1).

Author: ngeor

rusty_common/src/position.rs

@@ -32,3 +32,9 @@ impl Position {
         self.col
     }
 }
+
+impl Default for Position {
+    fn default() -> Self {
+        Self::start()
+    }
+}

rusty_linter/src/pre_linter/main.rs

@@ -9,6 +9,7 @@ use rusty_parser::*;
 // TYPE ... END TYPE -> stored in user_defined_types depends on CONST for resolving string length (AS STRING * some_const)
 // FUNCTION/SUB -> depends on resolver for resolving bare names and on user_defined_types to ensure types exist
 
+#[derive(Default)]
 struct MainContext {
     resolver: TypeResolverImpl,
     user_defined_types: UserDefinedTypes,
@@ -19,14 +20,7 @@ struct MainContext {
 }
 
 pub fn pre_lint_program(program: &Program) -> Result<PreLinterResult, LintErrorPos> {
-    let mut ctx = MainContext {
-        resolver: TypeResolverImpl::new(),
-        user_defined_types: Default::default(),
-        functions: SubprogramContext::new(),
-        subs: SubprogramContext::new(),
-        global_constants: Default::default(),
-        declaration_pos: Position::start(),
-    };
+    let mut ctx = MainContext::default();
     <MainContext as Visitor<Program>>::visit(&mut ctx, program)?;
     ctx.post_visit_functions()?;
     ctx.post_visit_subs()?;

rusty_linter/src/pre_linter/sub_program_context.rs

@@ -109,10 +109,6 @@ impl Implementations {
 }
 
 impl SubprogramContext {
-    pub fn new() -> Self {
-        Self::default()
-    }
-
     pub fn add_declaration(
         &mut self,
         bare_name: BareName,