Merge #987

987: Refactor maybe_item to use Marker argument r=pcpthm a=pcpthm

As suggested at <https://github.com/rust-analyzer/rust-analyzer/pull/980#issuecomment-473659745>.
For expression paring functions, changing signature
- from `fn(&mut Parser) -> Option<CompletedMarker>` to `fn(&mut Parser, Marker) -> Result<CompletedMarker, Marker>`
- from `fn(&mut Parser) -> CompletedMarker` to `fn(&mut Parser, Marker) -> CompletedMarker`
is my plan.

Co-authored-by: pcpthm <[email protected]>

2 files changed, 70 insertions, 84 deletions

diff --git a/crates/ra_parser/src/grammar/expressions.rs b/crates/ra_parser/src/grammar/expressions.rs
index 5a3b9f589..ccbc905ab 100644
--- a/crates/ra_parser/src/grammar/expressions.rs
+++ b/crates/ra_parser/src/grammar/expressions.rs
@@ -62,47 +62,41 @@ pub(crate) fn expr_block_contents(p: &mut Parser) {
             continue;
         }
 
-        match items::maybe_item(p, items::ItemFlavor::Mod) {
-            items::MaybeItem::Item(kind) => {
-                m.complete(p, kind);
-            }
-            items::MaybeItem::Modifiers => {
+        let m = match items::maybe_item(p, m, items::ItemFlavor::Mod) {
+            Ok(()) => continue,
+            Err(m) => m,
+        };
+
+        // test pub_expr
+        // fn foo() { pub 92; } //FIXME
+        if has_attrs {
+            m.abandon(p);
+            p.error("expected a let statement or an item after attributes in block");
+        } else {
+            let is_blocklike = expressions::expr_stmt(p) == BlockLike::Block;
+            if p.at(R_CURLY) {
                 m.abandon(p);
-                p.error("expected an item");
-            }
-            // test pub_expr
-            // fn foo() { pub 92; } //FIXME
-            items::MaybeItem::None => {
-                if has_attrs {
-                    m.abandon(p);
-                    p.error("expected a let statement or an item after attributes in block");
+            } else {
+                // test no_semi_after_block
+                // fn foo() {
+                //     if true {}
+                //     loop {}
+                //     match () {}
+                //     while true {}
+                //     for _ in () {}
+                //     {}
+                //     {}
+                //     macro_rules! test {
+                //          () => {}
+                //     }
+                //     test!{}
+                // }
+                if is_blocklike {
+                    p.eat(SEMI);
                 } else {
-                    let is_blocklike = expressions::expr_stmt(p) == BlockLike::Block;
-                    if p.at(R_CURLY) {
-                        m.abandon(p);
-                    } else {
-                        // test no_semi_after_block
-                        // fn foo() {
-                        //     if true {}
-                        //     loop {}
-                        //     match () {}
-                        //     while true {}
-                        //     for _ in () {}
-                        //     {}
-                        //     {}
-                        //     macro_rules! test {
-                        //          () => {}
-                        //     }
-                        //     test!{}
-                        // }
-                        if is_blocklike {
-                            p.eat(SEMI);
-                        } else {
-                            p.expect(SEMI);
-                        }
-                        m.complete(p, EXPR_STMT);
-                    }
+                    p.expect(SEMI);
                 }
+                m.complete(p, EXPR_STMT);
             }
         }
     }
diff --git a/crates/ra_parser/src/grammar/items.rs b/crates/ra_parser/src/grammar/items.rs
index a057c8167..94b93a02b 100644
--- a/crates/ra_parser/src/grammar/items.rs
+++ b/crates/ra_parser/src/grammar/items.rs
@@ -37,52 +37,40 @@ pub(super) const ITEM_RECOVERY_SET: TokenSet = token_set![
 pub(super) fn item_or_macro(p: &mut Parser, stop_on_r_curly: bool, flavor: ItemFlavor) {
     let m = p.start();
     attributes::outer_attributes(p);
-    match maybe_item(p, flavor) {
-        MaybeItem::Item(kind) => {
-            m.complete(p, kind);
-        }
-        MaybeItem::None => {
-            if paths::is_path_start(p) {
-                match macro_call(p) {
-                    BlockLike::Block => (),
-                    BlockLike::NotBlock => {
-                        p.expect(SEMI);
-                    }
-                }
-                m.complete(p, MACRO_CALL);
-            } else {
-                m.abandon(p);
-                if p.at(L_CURLY) {
-                    error_block(p, "expected an item");
-                } else if p.at(R_CURLY) && !stop_on_r_curly {
-                    let e = p.start();
-                    p.error("unmatched `}`");
-                    p.bump();
-                    e.complete(p, ERROR);
-                } else if !p.at(EOF) && !p.at(R_CURLY) {
-                    p.err_and_bump("expected an item");
-                } else {
-                    p.error("expected an item");
-                }
+    let m = match maybe_item(p, m, flavor) {
+        Ok(()) => return,
+        Err(m) => m,
+    };
+    if paths::is_path_start(p) {
+        match macro_call(p) {
+            BlockLike::Block => (),
+            BlockLike::NotBlock => {
+                p.expect(SEMI);
             }
         }
-        MaybeItem::Modifiers => {
-            p.error("expected fn, trait or impl");
-            m.complete(p, ERROR);
+        m.complete(p, MACRO_CALL);
+    } else {
+        m.abandon(p);
+        if p.at(L_CURLY) {
+            error_block(p, "expected an item");
+        } else if p.at(R_CURLY) && !stop_on_r_curly {
+            let e = p.start();
+            p.error("unmatched `}`");
+            p.bump();
+            e.complete(p, ERROR);
+        } else if !p.at(EOF) && !p.at(R_CURLY) {
+            p.err_and_bump("expected an item");
+        } else {
+            p.error("expected an item");
         }
     }
 }
 
-pub(super) enum MaybeItem {
-    None,
-    Item(SyntaxKind),
-    Modifiers,
-}
-
-pub(super) fn maybe_item(p: &mut Parser, flavor: ItemFlavor) -> MaybeItem {
+pub(super) fn maybe_item(p: &mut Parser, m: Marker, flavor: ItemFlavor) -> Result<(), Marker> {
     opt_visibility(p);
     if let Some(kind) = items_without_modifiers(p) {
-        return MaybeItem::Item(kind);
+        m.complete(p, kind);
+        return Ok(());
     }
 
     let mut has_mods = false;
@@ -115,7 +103,7 @@ pub(super) fn maybe_item(p: &mut Parser, flavor: ItemFlavor) -> MaybeItem {
     }
 
     // items
-    let kind = match p.current() {
+    match p.current() {
         // test async_fn
         // async fn foo() {}
 
@@ -135,7 +123,7 @@ pub(super) fn maybe_item(p: &mut Parser, flavor: ItemFlavor) -> MaybeItem {
         // unsafe fn foo() {}
         FN_KW => {
             fn_def(p, flavor);
-            FN_DEF
+            m.complete(p, FN_DEF);
         }
 
         // test unsafe_trait
@@ -148,7 +136,7 @@ pub(super) fn maybe_item(p: &mut Parser, flavor: ItemFlavor) -> MaybeItem {
         // unsafe auto trait T {}
         TRAIT_KW => {
             traits::trait_def(p);
-            TRAIT_DEF
+            m.complete(p, TRAIT_DEF);
         }
 
         // test unsafe_impl
@@ -161,14 +149,18 @@ pub(super) fn maybe_item(p: &mut Parser, flavor: ItemFlavor) -> MaybeItem {
         // unsafe default impl Foo {}
         IMPL_KW => {
             traits::impl_block(p);
-            IMPL_BLOCK
+            m.complete(p, IMPL_BLOCK);
         }
         _ => {
-            return if has_mods { MaybeItem::Modifiers } else { MaybeItem::None };
+            if !has_mods {
+                return Err(m);
+            } else {
+                p.error("expected fn, trait or impl");
+                m.complete(p, ERROR);
+            }
         }
-    };
-
-    MaybeItem::Item(kind)
+    }
+    Ok(())
 }
 
 fn items_without_modifiers(p: &mut Parser) -> Option<SyntaxKind> {