WIP: switch to fully decomposed tokens internally

12 files changed, 423 insertions, 280 deletions

diff --git a/crates/ra_parser/src/grammar.rs b/crates/ra_parser/src/grammar.rs
index 4e6f2f558..0158f9b8a 100644
--- a/crates/ra_parser/src/grammar.rs
+++ b/crates/ra_parser/src/grammar.rs
@@ -210,7 +210,7 @@ fn opt_visibility(p: &mut Parser) -> bool {
         //
         // test crate_keyword_path
         // fn foo() { crate::foo(); }
-        T![crate] if p.nth(1) != T![::] => {
+        T![crate] if !p.nth_at(1, T![::]) => {
             let m = p.start();
             p.bump_any();
             m.complete(p, VISIBILITY);
@@ -245,7 +245,7 @@ fn abi(p: &mut Parser) {
 fn opt_fn_ret_type(p: &mut Parser) -> bool {
     if p.at(T![->]) {
         let m = p.start();
-        p.bump_any();
+        p.bump(T![->]);
         types::type_(p);
         m.complete(p, RET_TYPE);
         true
diff --git a/crates/ra_parser/src/grammar/expressions.rs b/crates/ra_parser/src/grammar/expressions.rs
index 30036eb46..ea04b9458 100644
--- a/crates/ra_parser/src/grammar/expressions.rs
+++ b/crates/ra_parser/src/grammar/expressions.rs
@@ -212,52 +212,48 @@ struct Restrictions {
     prefer_stmt: bool,
 }
 
-enum Op {
-    Simple,
-    Composite(SyntaxKind, u8),
-}
-
-fn current_op(p: &Parser) -> (u8, Op) {
-    if let Some(t) = p.current3() {
-        match t {
-            (T![<], T![<], T![=]) => return (1, Op::Composite(T![<<=], 3)),
-            (T![>], T![>], T![=]) => return (1, Op::Composite(T![>>=], 3)),
-            _ => (),
-        }
-    }
-
-    if let Some(t) = p.current2() {
-        match t {
-            (T![+], T![=]) => return (1, Op::Composite(T![+=], 2)),
-            (T![-], T![=]) => return (1, Op::Composite(T![-=], 2)),
-            (T![*], T![=]) => return (1, Op::Composite(T![*=], 2)),
-            (T![%], T![=]) => return (1, Op::Composite(T![%=], 2)),
-            (T![/], T![=]) => return (1, Op::Composite(T![/=], 2)),
-            (T![|], T![=]) => return (1, Op::Composite(T![|=], 2)),
-            (T![&], T![=]) => return (1, Op::Composite(T![&=], 2)),
-            (T![^], T![=]) => return (1, Op::Composite(T![^=], 2)),
-            (T![|], T![|]) => return (3, Op::Composite(T![||], 2)),
-            (T![&], T![&]) => return (4, Op::Composite(T![&&], 2)),
-            (T![<], T![=]) => return (5, Op::Composite(T![<=], 2)),
-            (T![>], T![=]) => return (5, Op::Composite(T![>=], 2)),
-            (T![<], T![<]) => return (9, Op::Composite(T![<<], 2)),
-            (T![>], T![>]) => return (9, Op::Composite(T![>>], 2)),
-            _ => (),
-        }
+/// Binding powers of operators for a Pratt parser.
+///
+/// See https://www.oilshell.org/blog/2016/11/03.html
+#[rustfmt::skip]
+fn current_op(p: &Parser) -> (u8, SyntaxKind) {
+    const NOT_AN_OP: (u8, SyntaxKind) = (0, T![@]);
+    match p.current() {
+        T![|] if p.at(T![||])  => (3,  T![||]),
+        T![|] if p.at(T![|=])  => (1,  T![|=]),
+        T![|]                  => (6,  T![|]),
+        T![>] if p.at(T![>>=]) => (1,  T![>>=]),
+        T![>] if p.at(T![>>])  => (9,  T![>>]),
+        T![>] if p.at(T![>=])  => (5,  T![>=]),
+        T![>]                  => (5,  T![>]),
+        T![=] if p.at(T![=>])  => NOT_AN_OP,
+        T![=] if p.at(T![==])  => (5,  T![==]),
+        T![=]                  => (1,  T![=]),
+        T![<] if p.at(T![<=])  => (5,  T![<=]),
+        T![<] if p.at(T![<<=]) => (1,  T![<<=]),
+        T![<] if p.at(T![<<])  => (9,  T![<<]),
+        T![<]                  => (5,  T![<]),
+        T![+] if p.at(T![+=])  => (1,  T![+=]),
+        T![+]                  => (10, T![+]),
+        T![^] if p.at(T![^=])  => (1,  T![^=]),
+        T![^]                  => (7,  T![^]),
+        T![%] if p.at(T![%=])  => (1,  T![%=]),
+        T![%]                  => (11, T![%]),
+        T![&] if p.at(T![&=])  => (1,  T![&=]),
+        T![&] if p.at(T![&&])  => (4,  T![&&]),
+        T![&]                  => (8,  T![&]),
+        T![/] if p.at(T![/=])  => (1,  T![/=]),
+        T![/]                  => (11, T![/]),
+        T![*] if p.at(T![*=])  => (1,  T![*=]),
+        T![*]                  => (11, T![*]),
+        T![.] if p.at(T![..=]) => (2,  T![..=]),
+        T![.] if p.at(T![..])  => (2,  T![..]),
+        T![!] if p.at(T![!=])  => (5,  T![!=]),
+        T![-] if p.at(T![-=])  => (1,  T![-=]),
+        T![-]                  => (10, T![-]),
+
+        _                      => NOT_AN_OP
     }
-
-    let bp = match p.current() {
-        T![=] => 1,
-        T![..] | T![..=] => 2,
-        T![==] | T![!=] | T![<] | T![>] => 5,
-        T![|] => 6,
-        T![^] => 7,
-        T![&] => 8,
-        T![-] | T![+] => 10,
-        T![*] | T![/] | T![%] => 11,
-        _ => 0,
-    };
-    (bp, Op::Simple)
 }
 
 // Parses expression with binding power of at least bp.
@@ -308,12 +304,7 @@ fn expr_bp(
             break;
         }
         let m = lhs.precede(p);
-        match op {
-            Op::Simple => p.bump_any(),
-            Op::Composite(kind, n) => {
-                p.bump_compound(kind, n);
-            }
-        }
+        p.bump(op);
 
         expr_bp(p, r, op_bp + 1, dollar_lvl);
         lhs = m.complete(p, if is_range { RANGE_EXPR } else { BIN_EXPR });
@@ -321,8 +312,7 @@ fn expr_bp(
     (Some(lhs), BlockLike::NotBlock)
 }
 
-const LHS_FIRST: TokenSet =
-    atom::ATOM_EXPR_FIRST.union(token_set![AMP, STAR, EXCL, DOTDOT, DOTDOTEQ, MINUS]);
+const LHS_FIRST: TokenSet = atom::ATOM_EXPR_FIRST.union(token_set![AMP, STAR, EXCL, DOT, MINUS]);
 
 fn lhs(
     p: &mut Parser,
@@ -353,17 +343,20 @@ fn lhs(
             p.bump_any();
             PREFIX_EXPR
         }
-        // test full_range_expr
-        // fn foo() { xs[..]; }
-        T![..] | T![..=] => {
-            m = p.start();
-            p.bump_any();
-            if p.at_ts(EXPR_FIRST) {
-                expr_bp(p, r, 2, dollar_lvl);
-            }
-            return Some((m.complete(p, RANGE_EXPR), BlockLike::NotBlock));
-        }
         _ => {
+            // test full_range_expr
+            // fn foo() { xs[..]; }
+            for &op in [T![..=], T![..]].iter() {
+                if p.at(op) {
+                    m = p.start();
+                    p.bump(op);
+                    if p.at_ts(EXPR_FIRST) {
+                        expr_bp(p, r, 2, dollar_lvl);
+                    }
+                    return Some((m.complete(p, RANGE_EXPR), BlockLike::NotBlock));
+                }
+            }
+
             // test expression_after_block
             // fn foo() {
             //    let mut p = F{x: 5};
@@ -399,29 +392,13 @@ fn postfix_expr(
             // }
             T!['('] if allow_calls => call_expr(p, lhs),
             T!['['] if allow_calls => index_expr(p, lhs),
-            T![.] if p.nth(1) == IDENT && (p.nth(2) == T!['('] || p.nth(2) == T![::]) => {
-                method_call_expr(p, lhs)
-            }
-            T![.] if p.nth(1) == AWAIT_KW => {
-                // test await_expr
-                // fn foo() {
-                //     x.await;
-                //     x.0.await;
-                //     x.0().await?.hello();
-                // }
-                let m = lhs.precede(p);
-                p.bump_any();
-                p.bump_any();
-                m.complete(p, AWAIT_EXPR)
-            }
-            T![.] => field_expr(p, lhs),
-            // test postfix_range
-            // fn foo() { let x = 1..; }
-            T![..] | T![..=] if !EXPR_FIRST.contains(p.nth(1)) => {
-                let m = lhs.precede(p);
-                p.bump_any();
-                m.complete(p, RANGE_EXPR)
-            }
+            T![.] => match postfix_dot_expr(p, lhs) {
+                Ok(it) => it,
+                Err(it) => {
+                    lhs = it;
+                    break;
+                }
+            },
             T![?] => try_expr(p, lhs),
             T![as] => cast_expr(p, lhs),
             _ => break,
@@ -429,7 +406,46 @@ fn postfix_expr(
         allow_calls = true;
         block_like = BlockLike::NotBlock;
     }
-    (lhs, block_like)
+    return (lhs, block_like);
+
+    fn postfix_dot_expr(
+        p: &mut Parser,
+        lhs: CompletedMarker,
+    ) -> Result<CompletedMarker, CompletedMarker> {
+        assert!(p.at(T![.]));
+        if p.nth(1) == IDENT && (p.nth(2) == T!['('] || p.nth_at(2, T![::])) {
+            return Ok(method_call_expr(p, lhs));
+        }
+
+        // test await_expr
+        // fn foo() {
+        //     x.await;
+        //     x.0.await;
+        //     x.0().await?.hello();
+        // }
+        if p.nth(1) == T![await] {
+            let m = lhs.precede(p);
+            p.bump(T![.]);
+            p.bump(T![await]);
+            return Ok(m.complete(p, AWAIT_EXPR));
+        }
+
+        // test postfix_range
+        // fn foo() { let x = 1..; }
+        for &(op, la) in [(T![..=], 3), (T![..], 2)].iter() {
+            if p.at(op) {
+                return if EXPR_FIRST.contains(p.nth(la)) {
+                    Err(lhs)
+                } else {
+                    let m = lhs.precede(p);
+                    p.bump(op);
+                    Ok(m.complete(p, RANGE_EXPR))
+                };
+            }
+        }
+
+        Ok(field_expr(p, lhs))
+    }
 }
 
 // test call_expr
@@ -465,7 +481,7 @@ fn index_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
 //     y.bar::<T>(1, 2,);
 // }
 fn method_call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
-    assert!(p.at(T![.]) && p.nth(1) == IDENT && (p.nth(2) == T!['('] || p.nth(2) == T![::]));
+    assert!(p.at(T![.]) && p.nth(1) == IDENT && (p.nth(2) == T!['('] || p.nth_at(2, T![::])));
     let m = lhs.precede(p);
     p.bump_any();
     name_ref(p);
@@ -567,7 +583,7 @@ fn path_expr(p: &mut Parser, r: Restrictions) -> (CompletedMarker, BlockLike) {
             record_field_list(p);
             (m.complete(p, RECORD_LIT), BlockLike::NotBlock)
         }
-        T![!] => {
+        T![!] if !p.at(T![!=]) => {
             let block_like = items::macro_call_after_excl(p);
             (m.complete(p, MACRO_CALL), block_like)
         }
@@ -601,8 +617,8 @@ pub(crate) fn record_field_list(p: &mut Parser) {
                 }
                 m.complete(p, RECORD_FIELD);
             }
-            T![..] => {
-                p.bump_any();
+            T![.] if p.at(T![..]) => {
+                p.bump(T![..]);
                 expr(p);
             }
             T!['{'] => error_block(p, "expected a field"),
diff --git a/crates/ra_parser/src/grammar/items.rs b/crates/ra_parser/src/grammar/items.rs
index f27cc85ff..eff9d67e4 100644
--- a/crates/ra_parser/src/grammar/items.rs
+++ b/crates/ra_parser/src/grammar/items.rs
@@ -422,7 +422,7 @@ pub(crate) fn token_tree(p: &mut Parser) {
                 return;
             }
             T![')'] | T![']'] => p.err_and_bump("unmatched brace"),
-            _ => p.bump_raw(),
+            _ => p.bump_any(),
         }
     }
     p.expect(closing_paren_kind);
diff --git a/crates/ra_parser/src/grammar/items/use_item.rs b/crates/ra_parser/src/grammar/items/use_item.rs
index 7a1693a34..f28f522b8 100644
--- a/crates/ra_parser/src/grammar/items/use_item.rs
+++ b/crates/ra_parser/src/grammar/items/use_item.rs
@@ -13,9 +13,8 @@ pub(super) fn use_item(p: &mut Parser, m: Marker) {
 /// so handles both `some::path::{inner::path}` and `inner::path` in
 /// `use some::path::{inner::path};`
 fn use_tree(p: &mut Parser) {
-    let la = p.nth(1);
     let m = p.start();
-    match (p.current(), la) {
+    match p.current() {
         // Finish the use_tree for cases of e.g.
         // `use some::path::{self, *};` or `use *;`
         // This does not handle cases such as `use some::path::*`
@@ -28,15 +27,15 @@ fn use_tree(p: &mut Parser) {
         // use ::*;
         // use some::path::{*};
         // use some::path::{::*};
-        (T![*], _) => p.bump_any(),
-        (T![::], T![*]) => {
+        T![*] => p.bump(T![*]),
+        T![:] if p.at(T![::]) && p.nth(2) == T![*] => {
             // Parse `use ::*;`, which imports all from the crate root in Rust 2015
             // This is invalid inside a use_tree_list, (e.g. `use some::path::{::*}`)
             // but still parses and errors later: ('crate root in paths can only be used in start position')
             // FIXME: Add this error (if not out of scope)
             // In Rust 2018, it is always invalid (see above)
-            p.bump_any();
-            p.bump_any();
+            p.bump(T![::]);
+            p.bump(T![*]);
         }
         // Open a use tree list
         // Handles cases such as `use {some::path};` or `{inner::path}` in
@@ -47,10 +46,11 @@ fn use_tree(p: &mut Parser) {
         // use {path::from::root}; // Rust 2015
         // use ::{some::arbritrary::path}; // Rust 2015
         // use ::{{{crate::export}}}; // Nonsensical but perfectly legal nestnig
-        (T!['{'], _) | (T![::], T!['{']) => {
-            if p.at(T![::]) {
-                p.bump_any();
-            }
+        T!['{'] => {
+            use_tree_list(p);
+        }
+        T![:] if p.at(T![::]) && p.nth(2) == T!['{'] => {
+            p.bump(T![::]);
             use_tree_list(p);
         }
         // Parse a 'standard' path.
@@ -80,8 +80,8 @@ fn use_tree(p: &mut Parser) {
                     // use Trait as _;
                     opt_alias(p);
                 }
-                T![::] => {
-                    p.bump_any();
+                T![:] if p.at(T![::]) => {
+                    p.bump(T![::]);
                     match p.current() {
                         T![*] => {
                             p.bump_any();
diff --git a/crates/ra_parser/src/grammar/params.rs b/crates/ra_parser/src/grammar/params.rs
index 56e457325..5893b22fd 100644
--- a/crates/ra_parser/src/grammar/params.rs
+++ b/crates/ra_parser/src/grammar/params.rs
@@ -80,7 +80,7 @@ fn value_parameter(p: &mut Parser, flavor: Flavor) {
     match flavor {
         Flavor::OptionalType | Flavor::Normal => {
             patterns::pattern(p);
-            if p.at(T![:]) || flavor.type_required() {
+            if p.at(T![:]) && !p.at(T![::]) || flavor.type_required() {
                 types::ascription(p)
             }
         }
@@ -96,10 +96,11 @@ fn value_parameter(p: &mut Parser, flavor: Flavor) {
             // trait Foo {
             //     fn bar(_: u64, mut x: i32);
             // }
-            if (la0 == IDENT || la0 == T![_]) && la1 == T![:]
+            if (la0 == IDENT || la0 == T![_]) && la1 == T![:] && !p.nth_at(1, T![::])
                 || la0 == T![mut] && la1 == IDENT && la2 == T![:]
-                || la0 == T![&] && la1 == IDENT && la2 == T![:]
-                || la0 == T![&] && la1 == T![mut] && la2 == IDENT && la3 == T![:]
+                || la0 == T![&]
+                    && (la1 == IDENT && la2 == T![:] && !p.nth_at(2, T![::])
+                        || la1 == T![mut] && la2 == IDENT && la3 == T![:] && !p.nth_at(3, T![::]))
             {
                 patterns::pattern(p);
                 types::ascription(p);
diff --git a/crates/ra_parser/src/grammar/paths.rs b/crates/ra_parser/src/grammar/paths.rs
index 345c93f55..24b65128e 100644
--- a/crates/ra_parser/src/grammar/paths.rs
+++ b/crates/ra_parser/src/grammar/paths.rs
@@ -1,7 +1,7 @@
 use super::*;
 
 pub(super) const PATH_FIRST: TokenSet =
-    token_set![IDENT, SELF_KW, SUPER_KW, CRATE_KW, COLONCOLON, L_ANGLE];
+    token_set![IDENT, SELF_KW, SUPER_KW, CRATE_KW, COLON, L_ANGLE];
 
 pub(super) fn is_path_start(p: &Parser) -> bool {
     is_use_path_start(p) || p.at(T![<])
@@ -9,7 +9,8 @@ pub(super) fn is_path_start(p: &Parser) -> bool {
 
 pub(super) fn is_use_path_start(p: &Parser) -> bool {
     match p.current() {
-        IDENT | T![self] | T![super] | T![crate] | T![::] => true,
+        IDENT | T![self] | T![super] | T![crate] => true,
+        T![:] if p.at(T![::]) => true,
         _ => false,
     }
 }
@@ -38,13 +39,13 @@ fn path(p: &mut Parser, mode: Mode) {
     path_segment(p, mode, true);
     let mut qual = path.complete(p, PATH);
     loop {
-        let use_tree = match p.nth(1) {
+        let use_tree = match p.nth(2) {
             T![*] | T!['{'] => true,
             _ => false,
         };
         if p.at(T![::]) && !use_tree {
             let path = qual.precede(p);
-            p.bump_any();
+            p.bump(T![::]);
             path_segment(p, mode, false);
             let path = path.complete(p, PATH);
             qual = path;
diff --git a/crates/ra_parser/src/grammar/patterns.rs b/crates/ra_parser/src/grammar/patterns.rs
index d2f4296f8..dd1d25b07 100644
--- a/crates/ra_parser/src/grammar/patterns.rs
+++ b/crates/ra_parser/src/grammar/patterns.rs
@@ -34,17 +34,20 @@ pub(super) fn pattern_r(p: &mut Parser, recovery_set: TokenSet) {
         //         200 .. 301=> (),
         //     }
         // }
-        if p.at(T![...]) || p.at(T![..=]) || p.at(T![..]) {
-            let m = lhs.precede(p);
-            p.bump_any();
-            atom_pat(p, recovery_set);
-            m.complete(p, RANGE_PAT);
+        for &range_op in [T![...], T![..=], T![..]].iter() {
+            if p.at(range_op) {
+                let m = lhs.precede(p);
+                p.bump(range_op);
+                atom_pat(p, recovery_set);
+                m.complete(p, RANGE_PAT);
+                return;
+            }
         }
         // test marco_pat
         // fn main() {
         //     let m!(x) = 0;
         // }
-        else if lhs.kind() == PATH_PAT && p.at(T![!]) {
+        if lhs.kind() == PATH_PAT && p.at(T![!]) {
             let m = lhs.precede(p);
             items::macro_call_after_excl(p);
             m.complete(p, MACRO_CALL);
@@ -56,14 +59,16 @@ const PAT_RECOVERY_SET: TokenSet =
     token_set![LET_KW, IF_KW, WHILE_KW, LOOP_KW, MATCH_KW, R_PAREN, COMMA];
 
 fn atom_pat(p: &mut Parser, recovery_set: TokenSet) -> Option<CompletedMarker> {
-    // Checks the token after an IDENT to see if a pattern is a path (Struct { .. }) or macro
-    // (T![x]).
-    let is_path_or_macro_pat =
-        |la1| la1 == T![::] || la1 == T!['('] || la1 == T!['{'] || la1 == T![!];
-
     let m = match p.nth(0) {
         T![box] => box_pat(p),
-        T![ref] | T![mut] | IDENT if !is_path_or_macro_pat(p.nth(1)) => bind_pat(p, true),
+        T![ref] | T![mut] => bind_pat(p, true),
+        IDENT => match p.nth(1) {
+            // Checks the token after an IDENT to see if a pattern is a path (Struct { .. }) or macro
+            // (T![x]).
+            T!['('] | T!['{'] | T![!] => path_pat(p),
+            T![:] if p.nth_at(1, T![::]) => path_pat(p),
+            _ => bind_pat(p, true),
+        },
 
         _ if paths::is_use_path_start(p) => path_pat(p),
         _ if is_literal_pat_start(p) => literal_pat(p),
@@ -158,7 +163,7 @@ fn record_field_pat_list(p: &mut Parser) {
     p.bump_any();
     while !p.at(EOF) && !p.at(T!['}']) {
         match p.current() {
-            T![..] => p.bump_any(),
+            T![.] if p.at(T![..]) => p.bump(T![..]),
             IDENT if p.nth(1) == T![:] => record_field_pat(p),
             T!['{'] => error_block(p, "expected ident"),
             T![box] => {
@@ -237,7 +242,7 @@ fn slice_pat(p: &mut Parser) -> CompletedMarker {
 fn pat_list(p: &mut Parser, ket: SyntaxKind) {
     while !p.at(EOF) && !p.at(ket) {
         match p.current() {
-            T![..] => p.bump_any(),
+            T![.] if p.at(T![..]) => p.bump(T![..]),
             _ => {
                 if !p.at_ts(PATTERN_FIRST) {
                     p.error("expected a pattern");
diff --git a/crates/ra_parser/src/grammar/type_args.rs b/crates/ra_parser/src/grammar/type_args.rs
index e100af531..edc7d4ff2 100644
--- a/crates/ra_parser/src/grammar/type_args.rs
+++ b/crates/ra_parser/src/grammar/type_args.rs
@@ -2,19 +2,16 @@ use super::*;
 
 pub(super) fn opt_type_arg_list(p: &mut Parser, colon_colon_required: bool) {
     let m;
-    match (colon_colon_required, p.nth(0), p.nth(1)) {
-        (_, T![::], T![<]) => {
-            m = p.start();
-            p.bump_any();
-            p.bump_any();
-        }
-        (false, T![<], T![=]) => return,
-        (false, T![<], _) => {
-            m = p.start();
-            p.bump_any();
-        }
-        _ => return,
-    };
+    if p.at(T![::]) && p.nth(2) == T![<] {
+        m = p.start();
+        p.bump(T![::]);
+        p.bump(T![<]);
+    } else if !colon_colon_required && p.at(T![<]) && p.nth(1) != T![=] {
+        m = p.start();
+        p.bump(T![<]);
+    } else {
+        return;
+    }
 
     while !p.at(EOF) && !p.at(T![>]) {
         type_arg(p);
@@ -37,7 +34,7 @@ fn type_arg(p: &mut Parser) {
         }
         // test associated_type_bounds
         // fn print_all<T: Iterator<Item: Display>>(printables: T) {}
-        IDENT if p.nth(1) == T![:] => {
+        IDENT if p.nth(1) == T![:] && p.nth(2) != T![:] => {
             name_ref(p);
             type_params::bounds(p);
             m.complete(p, ASSOC_TYPE_ARG);
diff --git a/crates/ra_parser/src/parser.rs b/crates/ra_parser/src/parser.rs
index d8567e84b..a27cdc2ea 100644
--- a/crates/ra_parser/src/parser.rs
+++ b/crates/ra_parser/src/parser.rs
@@ -6,7 +6,7 @@ use crate::{
     event::Event,
     ParseError,
     SyntaxKind::{self, EOF, ERROR, TOMBSTONE},
-    Token, TokenSet, TokenSource, T,
+    TokenSet, TokenSource, T,
 };
 
 /// `Parser` struct provides the low-level API for
@@ -40,38 +40,6 @@ impl<'t> Parser<'t> {
         self.nth(0)
     }
 
-    /// Returns the kinds of the current two tokens, if they are not separated
-    /// by trivia.
-    ///
-    /// Useful for parsing things like `>>`.
-    pub(crate) fn current2(&self) -> Option<(SyntaxKind, SyntaxKind)> {
-        let c1 = self.nth(0);
-        let c2 = self.nth(1);
-
-        if self.token_source.current().is_jointed_to_next {
-            Some((c1, c2))
-        } else {
-            None
-        }
-    }
-
-    /// Returns the kinds of the current three tokens, if they are not separated
-    /// by trivia.
-    ///
-    /// Useful for parsing things like `=>>`.
-    pub(crate) fn current3(&self) -> Option<(SyntaxKind, SyntaxKind, SyntaxKind)> {
-        let c1 = self.nth(0);
-        let c2 = self.nth(1);
-        let c3 = self.nth(2);
-        if self.token_source.current().is_jointed_to_next
-            && self.token_source.lookahead_nth(1).is_jointed_to_next
-        {
-            Some((c1, c2, c3))
-        } else {
-            None
-        }
-    }
-
     /// Lookahead operation: returns the kind of the next nth
     /// token.
     pub(crate) fn nth(&self, n: usize) -> SyntaxKind {
@@ -81,33 +49,116 @@ impl<'t> Parser<'t> {
         assert!(steps <= 10_000_000, "the parser seems stuck");
         self.steps.set(steps + 1);
 
-        // It is beecause the Dollar will appear between nth
-        // Following code skips through it
-        let mut non_dollars_count = 0;
-        let mut i = 0;
+        self.token_source.lookahead_nth(n).kind
 
-        loop {
-            let token = self.token_source.lookahead_nth(i);
-            let mut kind = token.kind;
-            if let Some((composited, step)) = self.is_composite(token, i) {
-                kind = composited;
-                i += step;
-            } else {
-                i += 1;
-            }
+        // // It is because the Dollar will appear between nth
+        // // Following code skips through it
+        // let mut non_dollars_count = 0;
+        // let mut i = 0;
 
-            match kind {
-                EOF => return EOF,
-                SyntaxKind::L_DOLLAR | SyntaxKind::R_DOLLAR => {}
-                _ if non_dollars_count == n => return kind,
-                _ => non_dollars_count += 1,
-            }
-        }
+        // loop {
+        //     let token = self.token_source.lookahead_nth(i);
+        //     let mut kind = token.kind;
+        //     if let Some((composited, step)) = self.is_composite(token, i) {
+        //         kind = composited;
+        //         i += step;
+        //     } else {
+        //         i += 1;
+        //     }
+
+        //     match kind {
+        //         EOF => return EOF,
+        //         SyntaxKind::L_DOLLAR | SyntaxKind::R_DOLLAR => {}
+        //         _ if non_dollars_count == n => return kind,
+        //         _ => non_dollars_count += 1,
+        //     }
+        // }
     }
 
     /// Checks if the current token is `kind`.
     pub(crate) fn at(&self, kind: SyntaxKind) -> bool {
-        self.current() == kind
+        self.nth_at(0, kind)
+    }
+
+    pub(crate) fn nth_at(&self, n: usize, kind: SyntaxKind) -> bool {
+        match kind {
+            T![-=] => self.at_composite2(n, T![-], T![=]),
+            T![->] => self.at_composite2(n, T![-], T![>]),
+            T![::] => self.at_composite2(n, T![:], T![:]),
+            T![!=] => self.at_composite2(n, T![!], T![=]),
+            T![..] => self.at_composite2(n, T![.], T![.]),
+            T![*=] => self.at_composite2(n, T![*], T![=]),
+            T![/=] => self.at_composite2(n, T![/], T![=]),
+            T![&&] => self.at_composite2(n, T![&], T![&]),
+            T![&=] => self.at_composite2(n, T![&], T![=]),
+            T![%=] => self.at_composite2(n, T![%], T![=]),
+            T![^=] => self.at_composite2(n, T![^], T![=]),
+            T![+=] => self.at_composite2(n, T![+], T![=]),
+            T![<<] => self.at_composite2(n, T![<], T![<]),
+            T![<=] => self.at_composite2(n, T![<], T![=]),
+            T![==] => self.at_composite2(n, T![=], T![=]),
+            T![=>] => self.at_composite2(n, T![=], T![>]),
+            T![>=] => self.at_composite2(n, T![>], T![=]),
+            T![>>] => self.at_composite2(n, T![>], T![>]),
+            T![|=] => self.at_composite2(n, T![|], T![=]),
+            T![||] => self.at_composite2(n, T![|], T![|]),
+
+            T![...] => self.at_composite3(n, T![.], T![.], T![.]),
+            T![..=] => self.at_composite3(n, T![.], T![.], T![=]),
+            T![<<=] => self.at_composite3(n, T![<], T![<], T![=]),
+            T![>>=] => self.at_composite3(n, T![>], T![>], T![=]),
+
+            _ => self.token_source.lookahead_nth(n).kind == kind,
+        }
+    }
+
+    /// Consume the next token if `kind` matches.
+    pub(crate) fn eat(&mut self, kind: SyntaxKind) -> bool {
+        if !self.at(kind) {
+            return false;
+        }
+        let n_raw_tokens = match kind {
+            T![-=]
+            | T![->]
+            | T![::]
+            | T![!=]
+            | T![..]
+            | T![*=]
+            | T![/=]
+            | T![&&]
+            | T![&=]
+            | T![%=]
+            | T![^=]
+            | T![+=]
+            | T![<<]
+            | T![<=]
+            | T![==]
+            | T![=>]
+            | T![>=]
+            | T![>>]
+            | T![|=]
+            | T![||] => 2,
+
+            T![...] | T![..=] | T![<<=] | T![>>=] => 3,
+            _ => 1,
+        };
+        self.do_bump(kind, n_raw_tokens);
+        true
+    }
+
+    fn at_composite2(&self, n: usize, k1: SyntaxKind, k2: SyntaxKind) -> bool {
+        let t1 = self.token_source.lookahead_nth(n + 0);
+        let t2 = self.token_source.lookahead_nth(n + 1);
+        t1.kind == k1 && t1.is_jointed_to_next && t2.kind == k2
+    }
+
+    fn at_composite3(&self, n: usize, k1: SyntaxKind, k2: SyntaxKind, k3: SyntaxKind) -> bool {
+        let t1 = self.token_source.lookahead_nth(n + 0);
+        let t2 = self.token_source.lookahead_nth(n + 1);
+        let t3 = self.token_source.lookahead_nth(n + 2);
+        (t1.kind == k1 && t1.is_jointed_to_next)
+            && (t2.kind == k2 && t2.is_jointed_to_next)
+            && t3.kind == k3
     }
 
     /// Checks if the current token is in `kinds`.
@@ -129,9 +180,15 @@ impl<'t> Parser<'t> {
         Marker::new(pos)
     }
 
+    /// Consume the next token if `kind` matches.
+    pub(crate) fn bump(&mut self, kind: SyntaxKind) {
+        assert!(self.eat(kind));
+    }
+
     /// Advances the parser by one token unconditionally
     /// Mainly use in `token_tree` parsing
-    pub(crate) fn bump_raw(&mut self) {
+    #[allow(unused)]
+    fn bump_raw(&mut self) {
         let mut kind = self.token_source.current().kind;
 
         // Skip dollars, do_bump will eat these later
@@ -153,27 +210,7 @@ impl<'t> Parser<'t> {
         if kind == EOF {
             return;
         }
-
-        use SyntaxKind::*;
-
-        // Handle parser composites
-        match kind {
-            T![...] | T![..=] => {
-                self.bump_compound(kind, 3);
-            }
-            T![..] | T![::] | T![==] | T![=>] | T![!=] | T![->] => {
-                self.bump_compound(kind, 2);
-            }
-            _ => {
-                self.do_bump(kind, 1);
-            }
-        }
-    }
-
-    /// Advances the parser by one token, asserting that it is exactly the expected token
-    pub(crate) fn bump(&mut self, expected: SyntaxKind) {
-        debug_assert!(self.nth(0) == expected);
-        self.bump_any()
+        self.do_bump(kind, 1)
     }
 
     /// Advances the parser by one token, remapping its kind.
@@ -190,13 +227,6 @@ impl<'t> Parser<'t> {
         self.do_bump(kind, 1);
     }
 
-    /// Advances the parser by `n` tokens, remapping its kind.
-    /// This is useful to create compound tokens from parts. For
-    /// example, an `<<` token is two consecutive remapped `<` tokens
-    pub(crate) fn bump_compound(&mut self, kind: SyntaxKind, n: u8) {
-        self.do_bump(kind, n);
-    }
-
     /// Emit error with the `message`
     /// FIXME: this should be much more fancy and support
     /// structured errors with spans and notes, like rustc
@@ -206,15 +236,6 @@ impl<'t> Parser<'t> {
         self.push_event(Event::Error { msg })
     }
 
-    /// Consume the next token if `kind` matches.
-    pub(crate) fn eat(&mut self, kind: SyntaxKind) -> bool {
-        if !self.at(kind) {
-            return false;
-        }
-        self.bump_any();
-        true
-    }
-
     /// Consume the next token if it is `kind` or emit an error
     /// otherwise.
     pub(crate) fn expect(&mut self, kind: SyntaxKind) -> bool {
@@ -243,7 +264,7 @@ impl<'t> Parser<'t> {
     }
 
     fn do_bump(&mut self, kind: SyntaxKind, n_raw_tokens: u8) {
-        self.eat_dollars();
+        // self.eat_dollars();
 
         for _ in 0..n_raw_tokens {
             self.token_source.bump();
@@ -256,50 +277,7 @@ impl<'t> Parser<'t> {
         self.events.push(event)
     }
 
-    /// helper function for check if it is composite.
-    fn is_composite(&self, first: Token, n: usize) -> Option<(SyntaxKind, usize)> {
-        // We assume the dollars will not occuried between
-        // mult-byte tokens
-
-        let jn1 = first.is_jointed_to_next;
-        if !jn1 && first.kind != T![-] {
-            return None;
-        }
-
-        let second = self.token_source.lookahead_nth(n + 1);
-        if first.kind == T![-] && second.kind == T![>] {
-            return Some((T![->], 2));
-        }
-        if !jn1 {
-            return None;
-        }
-
-        match (first.kind, second.kind) {
-            (T![:], T![:]) => return Some((T![::], 2)),
-            (T![=], T![=]) => return Some((T![==], 2)),
-            (T![=], T![>]) => return Some((T![=>], 2)),
-            (T![!], T![=]) => return Some((T![!=], 2)),
-            _ => {}
-        }
-
-        if first.kind != T![.] || second.kind != T![.] {
-            return None;
-        }
-
-        let third = self.token_source.lookahead_nth(n + 2);
-
-        let jn2 = second.is_jointed_to_next;
-        let la3 = third.kind;
-
-        if jn2 && la3 == T![.] {
-            return Some((T![...], 3));
-        }
-        if la3 == T![=] {
-            return Some((T![..=], 3));
-        }
-        return Some((T![..], 2));
-    }
-
+    #[allow(unused)]
     fn eat_dollars(&mut self) {
         loop {
             match self.token_source.current().kind {
diff --git a/crates/ra_syntax/src/tests.rs b/crates/ra_syntax/src/tests.rs
index fa5d2d5d8..458920607 100644
--- a/crates/ra_syntax/src/tests.rs
+++ b/crates/ra_syntax/src/tests.rs
@@ -16,6 +16,18 @@ fn lexer_tests() {
 }
 
 #[test]
+fn parse_smoke_test() {
+    let code = r##"
+fn main() {
+    println!("Hello, world!")
+}
+    "##;
+
+    let parse = SourceFile::parse(code);
+    assert!(parse.ok().is_ok());
+}
+
+#[test]
 fn parser_tests() {
     dir_tests(&test_data_dir(), &["parser/inline/ok", "parser/ok"], |text, path| {
         let parse = SourceFile::parse(text);
@@ -75,7 +87,9 @@ fn self_hosting_parsing() {
     {
         count += 1;
         let text = read_text(entry.path());
-        SourceFile::parse(&text).ok().expect("There should be no errors in the file");
+        if let Err(errors) = SourceFile::parse(&text).ok() {
+            panic!("Parsing errors:\n{:?}\n{}\n", errors, entry.path().display());
+        }
     }
     assert!(
         count > 30,
diff --git a/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.rs b/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.rs
new file mode 100644
index 000000000..0d3f5722a
--- /dev/null
+++ b/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.rs
@@ -0,0 +1,5 @@
+fn a() -> Foo<bar::Baz> {}
+
+fn b(_: impl FnMut(x::Y)) {}
+
+fn c(_: impl FnMut(&x::Y)) {}
diff --git a/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.txt b/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.txt
new file mode 100644
index 000000000..7e1af254c
--- /dev/null
+++ b/crates/ra_syntax/test_data/parser/ok/0054_qual_path_in_type_arg.txt
@@ -0,0 +1,126 @@
+SOURCE_FILE@[0; 88)
+  FN_DEF@[0; 26)
+    FN_KW@[0; 2) "fn"
+    WHITESPACE@[2; 3) " "
+    NAME@[3; 4)
+      IDENT@[3; 4) "a"
+    PARAM_LIST@[4; 6)
+      L_PAREN@[4; 5) "("
+      R_PAREN@[5; 6) ")"
+    WHITESPACE@[6; 7) " "
+    RET_TYPE@[7; 23)
+      THIN_ARROW@[7; 9) "->"
+      WHITESPACE@[9; 10) " "
+      PATH_TYPE@[10; 23)
+        PATH@[10; 23)
+          PATH_SEGMENT@[10; 23)
+            NAME_REF@[10; 13)
+              IDENT@[10; 13) "Foo"
+            TYPE_ARG_LIST@[13; 23)
+              L_ANGLE@[13; 14) "<"
+              TYPE_ARG@[14; 22)
+                PATH_TYPE@[14; 22)
+                  PATH@[14; 22)
+                    PATH@[14; 17)
+                      PATH_SEGMENT@[14; 17)
+                        NAME_REF@[14; 17)
+                          IDENT@[14; 17) "bar"
+                    COLONCOLON@[17; 19) "::"
+                    PATH_SEGMENT@[19; 22)
+                      NAME_REF@[19; 22)
+                        IDENT@[19; 22) "Baz"
+              R_ANGLE@[22; 23) ">"
+    WHITESPACE@[23; 24) " "
+    BLOCK_EXPR@[24; 26)
+      BLOCK@[24; 26)
+        L_CURLY@[24; 25) "{"
+        R_CURLY@[25; 26) "}"
+  WHITESPACE@[26; 28) "\n\n"
+  FN_DEF@[28; 56)
+    FN_KW@[28; 30) "fn"
+    WHITESPACE@[30; 31) " "
+    NAME@[31; 32)
+      IDENT@[31; 32) "b"
+    PARAM_LIST@[32; 53)
+      L_PAREN@[32; 33) "("
+      PARAM@[33; 52)
+        PLACEHOLDER_PAT@[33; 34)
+          UNDERSCORE@[33; 34) "_"
+        COLON@[34; 35) ":"
+        WHITESPACE@[35; 36) " "
+        IMPL_TRAIT_TYPE@[36; 52)
+          IMPL_KW@[36; 40) "impl"
+          WHITESPACE@[40; 41) " "
+          TYPE_BOUND_LIST@[41; 52)
+            TYPE_BOUND@[41; 52)
+              PATH_TYPE@[41; 52)
+                PATH@[41; 52)
+                  PATH_SEGMENT@[41; 52)
+                    NAME_REF@[41; 46)
+                      IDENT@[41; 46) "FnMut"
+                    PARAM_LIST@[46; 52)
+                      L_PAREN@[46; 47) "("
+                      PARAM@[47; 51)
+                        PATH_TYPE@[47; 51)
+                          PATH@[47; 51)
+                            PATH@[47; 48)
+                              PATH_SEGMENT@[47; 48)
+                                NAME_REF@[47; 48)
+                                  IDENT@[47; 48) "x"
+                            COLONCOLON@[48; 50) "::"
+                            PATH_SEGMENT@[50; 51)
+                              NAME_REF@[50; 51)
+                                IDENT@[50; 51) "Y"
+                      R_PAREN@[51; 52) ")"
+      R_PAREN@[52; 53) ")"
+    WHITESPACE@[53; 54) " "
+    BLOCK_EXPR@[54; 56)
+      BLOCK@[54; 56)
+        L_CURLY@[54; 55) "{"
+        R_CURLY@[55; 56) "}"
+  WHITESPACE@[56; 58) "\n\n"
+  FN_DEF@[58; 87)
+    FN_KW@[58; 60) "fn"
+    WHITESPACE@[60; 61) " "
+    NAME@[61; 62)
+      IDENT@[61; 62) "c"
+    PARAM_LIST@[62; 84)
+      L_PAREN@[62; 63) "("
+      PARAM@[63; 83)
+        PLACEHOLDER_PAT@[63; 64)
+          UNDERSCORE@[63; 64) "_"
+        COLON@[64; 65) ":"
+        WHITESPACE@[65; 66) " "
+        IMPL_TRAIT_TYPE@[66; 83)
+          IMPL_KW@[66; 70) "impl"
+          WHITESPACE@[70; 71) " "
+          TYPE_BOUND_LIST@[71; 83)
+            TYPE_BOUND@[71; 83)
+              PATH_TYPE@[71; 83)
+                PATH@[71; 83)
+                  PATH_SEGMENT@[71; 83)
+                    NAME_REF@[71; 76)
+                      IDENT@[71; 76) "FnMut"
+                    PARAM_LIST@[76; 83)
+                      L_PAREN@[76; 77) "("
+                      PARAM@[77; 82)
+                        REFERENCE_TYPE@[77; 82)
+                          AMP@[77; 78) "&"
+                          PATH_TYPE@[78; 82)
+                            PATH@[78; 82)
+                              PATH@[78; 79)
+                                PATH_SEGMENT@[78; 79)
+                                  NAME_REF@[78; 79)
+                                    IDENT@[78; 79) "x"
+                              COLONCOLON@[79; 81) "::"
+                              PATH_SEGMENT@[81; 82)
+                                NAME_REF@[81; 82)
+                                  IDENT@[81; 82) "Y"
+                      R_PAREN@[82; 83) ")"
+      R_PAREN@[83; 84) ")"
+    WHITESPACE@[84; 85) " "
+    BLOCK_EXPR@[85; 87)
+      BLOCK@[85; 87)
+        L_CURLY@[85; 86) "{"
+        R_CURLY@[86; 87) "}"
+  WHITESPACE@[87; 88) "\n"