Add support for L?[x] list access syntax (#262)

I renamed the current `IndexKind` enum to `PropertyAccessKind` purely 
based off of the fact that somewhere in the byond ref both procs and 
vars are referred to as a datum's "properties" and I had no better name 
ideas.

The checker treats conditional list accesses exactly the same as normal 
ones. I was going to add some linting stuff for them but their expected 
behaviour is completely up in the air at the moment.

src/dreamchecker/lib.rs

@@ -1898,10 +1898,10 @@ impl<'o, 's> AnalyzeProc<'o, 's> {
 
     fn visit_follow(&mut self, location: Location, lhs: Analysis<'o>, rhs: &'o Follow, local_vars: &mut HashMap<String, LocalVar<'o>>) -> Analysis<'o> {
         match rhs {
-            Follow::Field(IndexKind::Colon, _) => Analysis::empty(),
-            Follow::Field(IndexKind::SafeColon, _) => Analysis::empty(),
-            Follow::Call(IndexKind::Colon, _, args) |
-            Follow::Call(IndexKind::SafeColon, _, args) => {
+            Follow::Field(PropertyAccessKind::Colon, _) => Analysis::empty(),
+            Follow::Field(PropertyAccessKind::SafeColon, _) => Analysis::empty(),
+            Follow::Call(PropertyAccessKind::Colon, _, args) |
+            Follow::Call(PropertyAccessKind::SafeColon, _, args) => {
                 // No analysis yet, but be sure to visit the arguments
                 for arg in args {
                     let mut argument_value = arg;
@@ -1920,7 +1920,7 @@ impl<'o, 's> AnalyzeProc<'o, 's> {
                 Analysis::empty()
             },
 
-            Follow::Index(expr) => {
+            Follow::Index(_, expr) => {
                 self.visit_expression(location, expr, None, local_vars);
                 // TODO: differentiate between L[1] and L[non_numeric_key]
                 match lhs.static_ty {

src/dreamchecker/tests/static_type_tests.rs

@@ -5,6 +5,7 @@ use dc::test_helpers::*;
 
 pub const FIELD_ACCESS_ERRORS: &[(u32, u16, &str)] = &[
     (3, 9, "field access requires static type: \"name\""),
+    (4, 10, "field access requires static type: \"name\""),
 ];
 
 #[test]
@@ -13,12 +14,14 @@ fn field_access() {
 /proc/test()
     var/list/L = list()
     L[1].name
+    L?[1].name
 "##.trim();
     check_errors_match(code, FIELD_ACCESS_ERRORS);
 }
 
 pub const PROC_CALL_ERRORS: &[(u32, u16, &str)] = &[
     (3, 9, "proc call requires static type: \"foo\""),
+    (4, 10, "proc call requires static type: \"foo\""),
 ];
 
 #[test]
@@ -27,6 +30,7 @@ fn proc_call() {
 /proc/test()
     var/list/L = list()
     L[1].foo()
+    L?[1].foo()
 /mob/proc/foo()
 "##.trim();
     check_errors_match(code, PROC_CALL_ERRORS);

src/dreamchecker/type_expr.rs

@@ -230,7 +230,7 @@ impl<'o> TypeExprCompiler<'o> {
     ) -> Result<TypeExpr<'o>, DMError> {
         match rhs {
             // X[_] => static type of argument X with one /list stripped
-            Follow::Index(expr) => match expr.as_term() {
+            Follow::Index(_, expr) => match expr.as_term() {
                 Some(Term::Ident(name)) if name == "_" => match lhs {
                     TypeExpr::ParamTypepath {
                         name,

src/dreammaker/ast.rs

@@ -639,9 +639,18 @@ impl From<Expression> for Term {
     }
 }
 
+/// The possible kinds of access operators for lists
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum ListAccessKind {
+    /// `[]`
+    Normal,
+    /// `?[]`
+    Safe,
+}
+
 /// The possible kinds of index operators, for both fields and methods.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum IndexKind {
+pub enum PropertyAccessKind {
     /// `a.b`
     Dot,
     /// `a:b`
@@ -652,18 +661,18 @@ pub enum IndexKind {
     SafeColon,
 }
 
-impl IndexKind {
+impl PropertyAccessKind {
     pub fn name(self) -> &'static str {
         match self {
-            IndexKind::Dot => ".",
-            IndexKind::Colon => ":",
-            IndexKind::SafeDot => "?.",
-            IndexKind::SafeColon => "?:",
+            PropertyAccessKind::Dot => ".",
+            PropertyAccessKind::Colon => ":",
+            PropertyAccessKind::SafeDot => "?.",
+            PropertyAccessKind::SafeColon => "?:",
         }
     }
 }
 
-impl fmt::Display for IndexKind {
+impl fmt::Display for PropertyAccessKind {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         fmt.write_str(self.name())
     }
@@ -673,17 +682,17 @@ impl fmt::Display for IndexKind {
 #[derive(Debug, Clone, PartialEq)]
 pub enum Follow {
     /// Index the value by an expression.
-    Index(Box<Expression>),
+    Index(ListAccessKind, Box<Expression>),
     /// Access a field of the value.
-    Field(IndexKind, Ident),
+    Field(PropertyAccessKind, Ident),
     /// Call a method of the value.
-    Call(IndexKind, Ident, Vec<Expression>),
+    Call(PropertyAccessKind, Ident, Vec<Expression>),
 }
 
 /// Like a `Follow` but only supports field accesses.
 #[derive(Debug, Clone, PartialEq)]
 pub struct Field {
-    pub kind: IndexKind,
+    pub kind: PropertyAccessKind,
     pub ident: Ident,
 }
 

src/dreammaker/lexer.rs

@@ -116,6 +116,7 @@ table! {
     "?",   QuestionMark;
     "?.",  SafeDot;
     "?:",  SafeColon;
+    "?[",  SafeLBracket;
     "[",   LBracket;
     "]",   RBracket;
     "^",   BitXor;
@@ -151,15 +152,15 @@ static SPEEDY_TABLE: [(usize, usize); 127] = [
     (2, 3), (3, 5), (5, 6), (6, 8), (0, 0), (8, 10), (10, 14), (14, 15),
     (15, 16), (16, 17), (17, 20), (20, 23), (23, 24), (24, 27), (27, 30), (30, 34),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
-    (0, 0), (0, 0), (34, 36), (36, 37), (37, 42), (42, 44), (44, 48), (48, 51),
+    (0, 0), (0, 0), (34, 36), (36, 37), (37, 42), (42, 44), (44, 48), (48, 52),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
-    (0, 0), (0, 0), (0, 0), (51, 52), (0, 0), (52, 53), (53, 55), (0, 0),
+    (0, 0), (0, 0), (0, 0), (52, 53), (0, 0), (53, 54), (54, 56), (0, 0),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
     (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0), (0, 0),
-    (0, 0), (0, 0), (0, 0), (55, 57), (57, 61), (61, 62), (62, 65)];
+    (0, 0), (0, 0), (0, 0), (56, 58), (58, 62), (62, 63), (63, 66)];
 
 #[test]
 fn make_speedy_table() {

src/dreammaker/parser.rs

@@ -2110,23 +2110,36 @@ impl<'ctx, 'an, 'inp> Parser<'ctx, 'an, 'inp> {
         success(Spanned::new(start, term))
     }
 
-    fn follow(&mut self, belongs_to: &mut Vec<Ident>, in_ternary: bool) -> Status<Spanned<Follow>> {
+    fn list_access(&mut self, belongs_to: &mut Vec<Ident>) -> Status<Spanned<Follow>> {
         let first_location = self.updated_location();
+
+        // follow :: ('[' | '?[') expression ']'
         let kind = match self.next("field access")? {
-            // follow :: '[' expression ']'
-            Token::Punct(Punctuation::LBracket) => {
-                belongs_to.clear();
-                let expr = require!(self.expression());
-                require!(self.exact(Token::Punct(Punctuation::RBracket)));
-                return success(Spanned::new(first_location, Follow::Index(Box::new(expr))))
-            }
+            Token::Punct(Punctuation::LBracket) => ListAccessKind::Normal,
+            Token::Punct(Punctuation::SafeLBracket) => ListAccessKind::Safe,
+            other => return self.try_another(other),
+        };
+
+        belongs_to.clear();
+        let expr = require!(self.expression());
+        require!(self.exact(Token::Punct(Punctuation::RBracket)));
+        success(Spanned::new(first_location, Follow::Index(kind, Box::new(expr))))
+    }
 
-            // follow :: '.' ident arglist?
+    fn follow(&mut self, belongs_to: &mut Vec<Ident>, in_ternary: bool) -> Status<Spanned<Follow>> {
+        let first_location = self.updated_location();
+
+        if let Some(follow) = self.list_access(belongs_to)? {
+            return success(follow);
+        }
+
+        // follow :: '.' ident arglist?
+        let kind = match self.next("field access")? {
             // TODO: only apply these rules if there is no whitespace around the punctuation
-            Token::Punct(Punctuation::Dot) => IndexKind::Dot,
-            Token::Punct(Punctuation::CloseColon) if !belongs_to.is_empty() || !in_ternary => IndexKind::Colon,
-            Token::Punct(Punctuation::SafeDot) => IndexKind::SafeDot,
-            Token::Punct(Punctuation::SafeColon) => IndexKind::SafeColon,
+            Token::Punct(Punctuation::Dot) => PropertyAccessKind::Dot,
+            Token::Punct(Punctuation::CloseColon) if !belongs_to.is_empty() || !in_ternary => PropertyAccessKind::Colon,
+            Token::Punct(Punctuation::SafeDot) => PropertyAccessKind::SafeDot,
+            Token::Punct(Punctuation::SafeColon) => PropertyAccessKind::SafeColon,
 
             other => return self.try_another(other),
         };
@@ -2172,10 +2185,10 @@ impl<'ctx, 'an, 'inp> Parser<'ctx, 'an, 'inp> {
         let kind = match self.next("field access")? {
             // follow :: '.' ident
             // TODO: only apply these rules if there is no whitespace around the punctuation
-            Token::Punct(Punctuation::Dot) => IndexKind::Dot,
-            Token::Punct(Punctuation::CloseColon) if !belongs_to.is_empty() || !in_ternary => IndexKind::Colon,
-            Token::Punct(Punctuation::SafeDot) => IndexKind::SafeDot,
-            Token::Punct(Punctuation::SafeColon) => IndexKind::SafeColon,
+            Token::Punct(Punctuation::Dot) => PropertyAccessKind::Dot,
+            Token::Punct(Punctuation::CloseColon) if !belongs_to.is_empty() || !in_ternary => PropertyAccessKind::Colon,
+            Token::Punct(Punctuation::SafeDot) => PropertyAccessKind::SafeDot,
+            Token::Punct(Punctuation::SafeColon) => PropertyAccessKind::SafeColon,
 
             other => return self.try_another(other),
         };

src/langserver/find_references.rs

@@ -564,7 +564,7 @@ impl<'o> WalkProc<'o> {
 
     fn visit_follow(&mut self, location: Location, lhs: StaticType<'o>, rhs: &'o Follow) -> StaticType<'o> {
         match rhs {
-            Follow::Index(expr) => {
+            Follow::Index(_, expr) => {
                 self.visit_expression(location, expr, None);
                 // TODO: call operator[] or operator[]=
                 // TODO: differentiate between L[1] and L[non_numeric_key]