From f2e82942dfc8ed544e82578a13c540084c4eae77 Mon Sep 17 00:00:00 2001
From: John Doty <john@d0ty.me>
Date: Mon, 29 Jan 2024 10:04:47 -0800
Subject: [PATCH] [fine] Some resilience, a design improvement for iterator

---
 fine/src/parser.rs                            | 24 +++++++++++++++----
 fine/tests/expression/alternates.fine         |  6 ++++-
 .../expression/errors/broken_conditional.fine |  1 -
 .../expression/errors/wild_member_access.fine |  6 ++++-
 4 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/fine/src/parser.rs b/fine/src/parser.rs
index e8bd273d..374260b7 100644
--- a/fine/src/parser.rs
+++ b/fine/src/parser.rs
@@ -318,6 +318,7 @@ struct CParser<'a> {
     current: Token<'a>,
     fuel: Cell<u32>,
     events: Vec<ParseEvent<'a>>,
+    panic: bool,
 }
 
 impl<'a> CParser<'a> {
@@ -327,6 +328,7 @@ impl<'a> CParser<'a> {
             current: Token::new(TokenKind::EOF, 0, ""),
             fuel: Cell::new(256),
             events: Vec::new(),
+            panic: false,
         };
         parser.current = parser.tokens.next();
         parser.skip_ephemera();
@@ -412,6 +414,7 @@ impl<'a> CParser<'a> {
 
     fn eat(&mut self, kind: TokenKind) -> bool {
         if self.at(kind) {
+            self.panic = false; // Check
             self.advance();
             true
         } else {
@@ -454,6 +457,11 @@ impl<'a> CParser<'a> {
     where
         T: Into<String>,
     {
+        if self.panic {
+            return;
+        }
+        self.panic = true;
+
         let message: String = message.into();
         let mut final_message = "Error ".to_string();
 
@@ -472,6 +480,10 @@ impl<'a> CParser<'a> {
         });
     }
 
+    fn synchronize(&mut self) {
+        if self.panic {}
+    }
+
     fn build_tree(self) -> (SyntaxTree<'a>, Lines) {
         let mut events = self.events;
         let mut stack = Vec::new();
@@ -599,21 +611,23 @@ fn field_decl(p: &mut CParser) {
     p.end(m, TreeKind::FieldDecl);
 }
 
-const PARAM_LIST_RECOVERY: &[TokenKind] = &[TokenKind::Arrow, TokenKind::LeftBrace, TokenKind::Fun];
+const PARAM_LIST_RECOVERY: &[TokenKind] = &[
+    TokenKind::Arrow,
+    TokenKind::LeftBrace,
+    TokenKind::Fun,
+    TokenKind::RightParen,
+];
 
 fn param_list(p: &mut CParser) {
     let m = p.start();
 
     p.expect_start(TokenKind::LeftParen);
-    while !p.at(TokenKind::RightParen) && !p.eof() {
+    while !p.at_any(PARAM_LIST_RECOVERY) && !p.eof() {
         if p.at(TokenKind::Identifier) {
             parameter(p);
         } else if p.at(TokenKind::Selff) {
             self_parameter(p);
         } else {
-            if p.at_any(PARAM_LIST_RECOVERY) {
-                break;
-            }
             p.advance_with_error("expected parameter");
         }
     }
diff --git a/fine/tests/expression/alternates.fine b/fine/tests/expression/alternates.fine
index 8ee2ebb4..79304484 100644
--- a/fine/tests/expression/alternates.fine
+++ b/fine/tests/expression/alternates.fine
@@ -83,16 +83,20 @@ fun more_examples(weapon: MeleeWeapon or RangedWeapon) -> f64 or () {
 }
 
 // Some fun with iterators
+class Finished {}
+let FINISHED = new Finished {}
 
 class Iterator {
   current: f64;
 
-  fun next(self) -> f64 or () {
+  fun next(self) -> f64 or Finished {
     if self.current < 10 {
       let result = self.current;
       self.current = self.current + 1;
       return result;
     }
+
+    FINISHED
   }
 }
 
diff --git a/fine/tests/expression/errors/broken_conditional.fine b/fine/tests/expression/errors/broken_conditional.fine
index 84efd0cb..dbcfe35c 100644
--- a/fine/tests/expression/errors/broken_conditional.fine
+++ b/fine/tests/expression/errors/broken_conditional.fine
@@ -5,4 +5,3 @@ fun test() {
 // NOTE: These errors should be better
 // @expect-errors:
 // | 2:10: Error at 'true': expected a block after `if`
-// | 2:15: Error at '{': expect ';' to end an expression statement
diff --git a/fine/tests/expression/errors/wild_member_access.fine b/fine/tests/expression/errors/wild_member_access.fine
index 649b6f2d..f1c47c2d 100644
--- a/fine/tests/expression/errors/wild_member_access.fine
+++ b/fine/tests/expression/errors/wild_member_access.fine
@@ -11,8 +11,12 @@ fun test() {
 //       We need to make sure things are parsed correctly.
 //
 // TODO: Better parser recovery will improve the specifics of the errors.
+//
+// TODO: This is parsed wrong; the `{` is consumed after the '.' and it
+// should instead be ignored. This is the "greedy" expression parsing that
+// matklad talks about in his resilient parser article.
+//
 // @expect-errors:
 // | 7:12: Error at '{': expected an expression
-// | 7:13: Error at 'let': expect ';' to end a let statement
 // | 7:26: cannot find value foo here
 // | 8:0: Error at '}': unbalanced '}'