2 files changed, 727 insertions, 0 deletions

diff --git a/crates/libsyntax2/src/grammar/expressions/atom.rs b/crates/libsyntax2/src/grammar/expressions/atom.rs
new file mode 100644
index 000000000..af9f47c5e
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/expressions/atom.rs
@@ -0,0 +1,348 @@
+use super::*;
+
+// test expr_literals
+// fn foo() {
+//     let _ = true;
+//     let _ = false;
+//     let _ = 1;
+//     let _ = 2.0;
+//     let _ = b'a';
+//     let _ = 'b';
+//     let _ = "c";
+//     let _ = r"d";
+//     let _ = b"e";
+//     let _ = br"f";
+// }
+const LITERAL_FIRST: TokenSet =
+    token_set![TRUE_KW, FALSE_KW, INT_NUMBER, FLOAT_NUMBER, BYTE, CHAR,
+               STRING, RAW_STRING, BYTE_STRING, RAW_BYTE_STRING];
+
+pub(crate) fn literal(p: &mut Parser) -> Option<CompletedMarker> {
+    if !LITERAL_FIRST.contains(p.current()) {
+        return None;
+    }
+    let m = p.start();
+    p.bump();
+    Some(m.complete(p, LITERAL))
+}
+
+pub(super) const ATOM_EXPR_FIRST: TokenSet =
+    token_set_union![
+        LITERAL_FIRST,
+        token_set![L_PAREN, PIPE, MOVE_KW, IF_KW, WHILE_KW, MATCH_KW, UNSAFE_KW, L_CURLY, RETURN_KW,
+                   IDENT, SELF_KW, SUPER_KW, COLONCOLON ],
+    ];
+
+pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<CompletedMarker> {
+    match literal(p) {
+        Some(m) => return Some(m),
+        None => (),
+    }
+    if paths::is_path_start(p) {
+        return Some(path_expr(p, r));
+    }
+    let la = p.nth(1);
+    let done = match p.current() {
+        L_PAREN => tuple_expr(p),
+        L_BRACK => array_expr(p),
+        PIPE => lambda_expr(p),
+        MOVE_KW if la == PIPE => lambda_expr(p),
+        IF_KW => if_expr(p),
+        WHILE_KW => while_expr(p),
+        LOOP_KW => loop_expr(p),
+        FOR_KW => for_expr(p),
+        MATCH_KW => match_expr(p),
+        UNSAFE_KW if la == L_CURLY => block_expr(p),
+        L_CURLY => block_expr(p),
+        RETURN_KW => return_expr(p),
+        _ => {
+            p.err_and_bump("expected expression");
+            return None;
+        }
+    };
+    Some(done)
+}
+
+// test tuple_expr
+// fn foo() {
+//     ();
+//     (1);
+//     (1,);
+// }
+fn tuple_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    p.expect(L_PAREN);
+
+    let mut saw_comma = false;
+    let mut saw_expr = false;
+    while !p.at(EOF) && !p.at(R_PAREN) {
+        saw_expr = true;
+        expr(p);
+        if !p.at(R_PAREN) {
+            saw_comma = true;
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_PAREN);
+    m.complete(p, if saw_expr && !saw_comma { PAREN_EXPR } else { TUPLE_EXPR })
+}
+
+// test array_expr
+// fn foo() {
+//     [];
+//     [1];
+//     [1, 2,];
+//     [1; 2];
+// }
+fn array_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_BRACK));
+    let m = p.start();
+    p.bump();
+    if p.eat(R_BRACK) {
+        return m.complete(p, ARRAY_EXPR);
+    }
+    expr(p);
+    if p.eat(SEMI) {
+        expr(p);
+        p.expect(R_BRACK);
+        return m.complete(p, ARRAY_EXPR);
+    }
+    while !p.at(EOF) && !p.at(R_BRACK) {
+        p.expect(COMMA);
+        if !p.at(R_BRACK) {
+            expr(p);
+        }
+    }
+    p.expect(R_BRACK);
+    m.complete(p, ARRAY_EXPR)
+}
+
+// test lambda_expr
+// fn foo() {
+//     || ();
+//     || -> i32 { 92 };
+//     |x| x;
+//     move |x: i32,| x;
+// }
+fn lambda_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(PIPE) || (p.at(MOVE_KW) && p.nth(1) == PIPE));
+    let m = p.start();
+    p.eat(MOVE_KW);
+    params::param_list_opt_types(p);
+    if fn_ret_type(p) {
+        block(p);
+    } else {
+        expr(p);
+    }
+    m.complete(p, LAMBDA_EXPR)
+}
+
+// test if_expr
+// fn foo() {
+//     if true {};
+//     if true {} else {};
+//     if true {} else if false {} else {};
+//     if S {};
+// }
+fn if_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(IF_KW));
+    let m = p.start();
+    p.bump();
+    cond(p);
+    block(p);
+    if p.at(ELSE_KW) {
+        p.bump();
+        if p.at(IF_KW) {
+            if_expr(p);
+        } else {
+            block(p);
+        }
+    }
+    m.complete(p, IF_EXPR)
+}
+
+// test while_expr
+// fn foo() {
+//     while true {};
+//     while let Some(x) = it.next() {};
+// }
+fn while_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(WHILE_KW));
+    let m = p.start();
+    p.bump();
+    cond(p);
+    block(p);
+    m.complete(p, WHILE_EXPR)
+}
+
+// test loop_expr
+// fn foo() {
+//     loop {};
+// }
+fn loop_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(LOOP_KW));
+    let m = p.start();
+    p.bump();
+    block(p);
+    m.complete(p, LOOP_EXPR)
+}
+
+// test for_expr
+// fn foo() {
+//     for x in [] {};
+// }
+fn for_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(FOR_KW));
+    let m = p.start();
+    p.bump();
+    patterns::pattern(p);
+    p.expect(IN_KW);
+    expr_no_struct(p);
+    block(p);
+    m.complete(p, FOR_EXPR)
+}
+
+// test cond
+// fn foo() { if let Some(_) = None {} }
+fn cond(p: &mut Parser) {
+    if p.eat(LET_KW) {
+        patterns::pattern(p);
+        p.expect(EQ);
+    }
+    expr_no_struct(p)
+}
+
+// test match_expr
+// fn foo() {
+//     match () { };
+//     match S {};
+// }
+fn match_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(MATCH_KW));
+    let m = p.start();
+    p.bump();
+    expr_no_struct(p);
+    p.eat(L_CURLY);
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        // test match_arms_commas
+        // fn foo() {
+        //     match () {
+        //         _ => (),
+        //         _ => {}
+        //         _ => ()
+        //     }
+        // }
+        if match_arm(p).is_block() {
+            p.eat(COMMA);
+        } else if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+    m.complete(p, MATCH_EXPR)
+}
+
+// test match_arm
+// fn foo() {
+//     match () {
+//         _ => (),
+//         X | Y if Z => (),
+//     };
+// }
+fn match_arm(p: &mut Parser) -> BlockLike {
+    let m = p.start();
+    loop {
+        patterns::pattern(p);
+        if !p.eat(PIPE) {
+            break;
+        }
+    }
+    if p.eat(IF_KW) {
+        expr_no_struct(p);
+    }
+    p.expect(FAT_ARROW);
+    let ret = expr_stmt(p);
+    m.complete(p, MATCH_ARM);
+    ret
+}
+
+// test block_expr
+// fn foo() {
+//     {};
+//     unsafe {};
+// }
+pub(super) fn block_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_CURLY) || p.at(UNSAFE_KW) && p.nth(1) == L_CURLY);
+    let m = p.start();
+    p.eat(UNSAFE_KW);
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        match p.current() {
+            LET_KW => let_stmt(p),
+            _ => {
+                // test block_items
+                // fn a() { fn b() {} }
+                let m = p.start();
+                match items::maybe_item(p) {
+                    items::MaybeItem::Item(kind) => {
+                        m.complete(p, kind);
+                    }
+                    items::MaybeItem::Modifiers => {
+                        m.abandon(p);
+                        p.error("expected an item");
+                    }
+                    // test pub_expr
+                    // fn foo() { pub 92; } //FIXME
+                    items::MaybeItem::None => {
+                        let is_blocklike = expressions::expr_stmt(p) == BlockLike::Block;
+                        if p.eat(SEMI) || (is_blocklike && !p.at(R_CURLY)) {
+                            m.complete(p, EXPR_STMT);
+                        } else {
+                            m.abandon(p);
+                        }
+                    }
+                }
+            }
+        }
+    }
+    p.expect(R_CURLY);
+    m.complete(p, BLOCK_EXPR)
+}
+
+// test let_stmt;
+// fn foo() {
+//     let a;
+//     let b: i32;
+//     let c = 92;
+//     let d: i32 = 92;
+// }
+fn let_stmt(p: &mut Parser) {
+    assert!(p.at(LET_KW));
+    let m = p.start();
+    p.bump();
+    patterns::pattern(p);
+    if p.at(COLON) {
+        types::ascription(p);
+    }
+    if p.eat(EQ) {
+        expressions::expr(p);
+    }
+    p.expect(SEMI);
+    m.complete(p, LET_STMT);
+}
+
+// test return_expr
+// fn foo() {
+//     return;
+//     return 92;
+// }
+fn return_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(RETURN_KW));
+    let m = p.start();
+    p.bump();
+    if EXPR_FIRST.contains(p.current()) {
+        expr(p);
+    }
+    m.complete(p, RETURN_EXPR)
+}
diff --git a/crates/libsyntax2/src/grammar/expressions/mod.rs b/crates/libsyntax2/src/grammar/expressions/mod.rs
new file mode 100644
index 000000000..dcbb1e2a8
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/expressions/mod.rs
@@ -0,0 +1,379 @@
+mod atom;
+
+use super::*;
+pub(super) use self::atom::literal;
+
+const EXPR_FIRST: TokenSet = LHS_FIRST;
+
+pub(super) fn expr(p: &mut Parser) -> BlockLike {
+    let r = Restrictions { forbid_structs: false, prefer_stmt: false };
+    expr_bp(p, r, 1)
+}
+
+pub(super) fn expr_stmt(p: &mut Parser) -> BlockLike {
+    let r = Restrictions { forbid_structs: false, prefer_stmt: true };
+    expr_bp(p, r, 1)
+}
+
+fn expr_no_struct(p: &mut Parser) {
+    let r = Restrictions { forbid_structs: true, prefer_stmt: false };
+    expr_bp(p, r, 1);
+}
+
+// test block
+// fn a() {}
+// fn b() { let _ = 1; }
+// fn c() { 1; 2; }
+// fn d() { 1; 2 }
+pub(super) fn block(p: &mut Parser) {
+    if !p.at(L_CURLY) {
+        p.error("expected block");
+        return;
+    }
+    atom::block_expr(p);
+}
+
+#[derive(Clone, Copy)]
+struct Restrictions {
+    forbid_structs: bool,
+    prefer_stmt: bool,
+}
+
+enum Op {
+    Simple,
+    Composite(SyntaxKind, u8),
+}
+
+fn current_op(p: &Parser) -> (u8, Op) {
+    if p.at_compound2(PLUS, EQ) {
+        return (1, Op::Composite(PLUSEQ, 2));
+    }
+    if p.at_compound2(MINUS, EQ) {
+        return (1, Op::Composite(MINUSEQ, 2));
+    }
+    if p.at_compound3(L_ANGLE, L_ANGLE, EQ) {
+        return (1, Op::Composite(SHLEQ, 3));
+    }
+    if p.at_compound3(R_ANGLE, R_ANGLE, EQ) {
+        return (1, Op::Composite(SHREQ, 3));
+    }
+    if p.at_compound2(PIPE, PIPE) {
+        return (3, Op::Composite(PIPEPIPE, 2));
+    }
+    if p.at_compound2(AMP, AMP) {
+        return (4, Op::Composite(AMPAMP, 2));
+    }
+    if p.at_compound2(L_ANGLE, EQ) {
+        return (5, Op::Composite(LTEQ, 2));
+    }
+    if p.at_compound2(R_ANGLE, EQ) {
+        return (5, Op::Composite(GTEQ, 2));
+    }
+    if p.at_compound2(L_ANGLE, L_ANGLE) {
+        return (9, Op::Composite(SHL, 2));
+    }
+    if p.at_compound2(R_ANGLE, R_ANGLE) {
+        return (9, Op::Composite(SHR, 2));
+    }
+
+    let bp = match p.current() {
+        EQ => 1,
+        DOTDOT => 2,
+        EQEQ | NEQ | L_ANGLE | R_ANGLE => 5,
+        PIPE => 6,
+        CARET => 7,
+        AMP => 8,
+        MINUS | PLUS => 10,
+        STAR | SLASH | PERCENT => 11,
+        _ => 0,
+    };
+    (bp, Op::Simple)
+}
+
+// Parses expression with binding power of at least bp.
+fn expr_bp(p: &mut Parser, r: Restrictions, bp: u8) -> BlockLike {
+    let mut lhs = match lhs(p, r) {
+        Some(lhs) => {
+            // test stmt_bin_expr_ambiguity
+            // fn foo() {
+            //     let _ = {1} & 2;
+            //     {1} &2;
+            // }
+            if r.prefer_stmt && is_block(lhs.kind()) {
+                return BlockLike::Block;
+            }
+            lhs
+        }
+        None => return BlockLike::NotBlock,
+    };
+
+    loop {
+        let is_range = p.current() == DOTDOT;
+        let (op_bp, op) = current_op(p);
+        if op_bp < bp {
+            break;
+        }
+        let m = lhs.precede(p);
+        match op {
+            Op::Simple => p.bump(),
+            Op::Composite(kind, n) => {
+                p.bump_compound(kind, n);
+            }
+        }
+        expr_bp(p, r, op_bp + 1);
+        lhs = m.complete(p, if is_range { RANGE_EXPR } else { BIN_EXPR });
+    }
+    BlockLike::NotBlock
+}
+
+// test no_semi_after_block
+// fn foo() {
+//     if true {}
+//     loop {}
+//     match () {}
+//     while true {}
+//     for _ in () {}
+//     {}
+//     {}
+// }
+fn is_block(kind: SyntaxKind) -> bool {
+    match kind {
+        IF_EXPR | WHILE_EXPR | FOR_EXPR | LOOP_EXPR | MATCH_EXPR | BLOCK_EXPR => true,
+        _ => false,
+    }
+}
+
+const LHS_FIRST: TokenSet =
+    token_set_union![
+        token_set![AMP, STAR, EXCL, DOTDOT, MINUS],
+        atom::ATOM_EXPR_FIRST,
+    ];
+
+fn lhs(p: &mut Parser, r: Restrictions) -> Option<CompletedMarker> {
+    let m;
+    let kind = match p.current() {
+        // test ref_expr
+        // fn foo() {
+        //     let _ = &1;
+        //     let _ = &mut &f();
+        // }
+        AMP => {
+            m = p.start();
+            p.bump();
+            p.eat(MUT_KW);
+            REF_EXPR
+        }
+        // test unary_expr
+        // fn foo() {
+        //     **&1;
+        //     !!true;
+        //     --1;
+        // }
+        STAR | EXCL | MINUS => {
+            m = p.start();
+            p.bump();
+            PREFIX_EXPR
+        }
+        DOTDOT => {
+            m = p.start();
+            p.bump();
+            expr_bp(p, r, 2);
+            return Some(m.complete(p, RANGE_EXPR));
+        }
+        _ => {
+            let lhs = atom::atom_expr(p, r)?;
+            return Some(postfix_expr(p, r, lhs));
+        }
+    };
+    expr_bp(p, r, 255);
+    Some(m.complete(p, kind))
+}
+
+fn postfix_expr(p: &mut Parser, r: Restrictions, mut lhs: CompletedMarker) -> CompletedMarker {
+    let mut allow_calls = !r.prefer_stmt || !is_block(lhs.kind());
+    loop {
+        lhs = match p.current() {
+            // test stmt_postfix_expr_ambiguity
+            // fn foo() {
+            //     match () {
+            //         _ => {}
+            //         () => {}
+            //         [] => {}
+            //     }
+            // }
+            L_PAREN if allow_calls => call_expr(p, lhs),
+            L_BRACK if allow_calls => index_expr(p, lhs),
+            DOT if p.nth(1) == IDENT => if p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON {
+                method_call_expr(p, lhs)
+            } else {
+                field_expr(p, lhs)
+            },
+            DOT if p.nth(1) == INT_NUMBER => field_expr(p, lhs),
+            // test postfix_range
+            // fn foo() { let x = 1..; }
+            DOTDOT if !EXPR_FIRST.contains(p.nth(1)) => {
+                let m = lhs.precede(p);
+                p.bump();
+                m.complete(p, RANGE_EXPR)
+            }
+            QUESTION => try_expr(p, lhs),
+            AS_KW => cast_expr(p, lhs),
+            _ => break,
+        };
+        allow_calls = true
+    }
+    lhs
+}
+
+// test call_expr
+// fn foo() {
+//     let _ = f();
+//     let _ = f()(1)(1, 2,);
+// }
+fn call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(L_PAREN));
+    let m = lhs.precede(p);
+    arg_list(p);
+    m.complete(p, CALL_EXPR)
+}
+
+// test index_expr
+// fn foo() {
+//     x[1][2];
+// }
+fn index_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(L_BRACK));
+    let m = lhs.precede(p);
+    p.bump();
+    expr(p);
+    p.expect(R_BRACK);
+    m.complete(p, INDEX_EXPR)
+}
+
+// test method_call_expr
+// fn foo() {
+//     x.foo();
+//     y.bar::<T>(1, 2,);
+// }
+fn method_call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(
+        p.at(DOT) && p.nth(1) == IDENT
+            && (p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON)
+    );
+    let m = lhs.precede(p);
+    p.bump();
+    name_ref(p);
+    type_args::type_arg_list(p, true);
+    arg_list(p);
+    m.complete(p, METHOD_CALL_EXPR)
+}
+
+// test field_expr
+// fn foo() {
+//     x.foo;
+//     x.0.bar;
+// }
+fn field_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(DOT) && (p.nth(1) == IDENT || p.nth(1) == INT_NUMBER));
+    let m = lhs.precede(p);
+    p.bump();
+    if p.at(IDENT) {
+        name_ref(p)
+    } else {
+        p.bump()
+    }
+    m.complete(p, FIELD_EXPR)
+}
+
+// test try_expr
+// fn foo() {
+//     x?;
+// }
+fn try_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(QUESTION));
+    let m = lhs.precede(p);
+    p.bump();
+    m.complete(p, TRY_EXPR)
+}
+
+// test cast_expr
+// fn foo() {
+//     82 as i32;
+// }
+fn cast_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(AS_KW));
+    let m = lhs.precede(p);
+    p.bump();
+    types::type_(p);
+    m.complete(p, CAST_EXPR)
+}
+
+fn arg_list(p: &mut Parser) {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    p.bump();
+    while !p.at(R_PAREN) && !p.at(EOF) {
+        expr(p);
+        if !p.at(R_PAREN) && !p.expect(COMMA) {
+            break;
+        }
+    }
+    p.eat(R_PAREN);
+    m.complete(p, ARG_LIST);
+}
+
+// test path_expr
+// fn foo() {
+//     let _ = a;
+//     let _ = a::b;
+//     let _ = ::a::<b>;
+//     let _ = format!();
+// }
+fn path_expr(p: &mut Parser, r: Restrictions) -> CompletedMarker {
+    assert!(paths::is_path_start(p));
+    let m = p.start();
+    paths::expr_path(p);
+    match p.current() {
+        L_CURLY if !r.forbid_structs => {
+            struct_lit(p);
+            m.complete(p, STRUCT_LIT)
+        }
+        EXCL => {
+            items::macro_call_after_excl(p);
+            m.complete(p, MACRO_CALL)
+        }
+        _ => m.complete(p, PATH_EXPR)
+    }
+}
+
+// test struct_lit
+// fn foo() {
+//     S {};
+//     S { x, y: 32, };
+//     S { x, y: 32, ..Default::default() };
+// }
+fn struct_lit(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        match p.current() {
+            IDENT => {
+                let m = p.start();
+                name_ref(p);
+                if p.eat(COLON) {
+                    expr(p);
+                }
+                m.complete(p, STRUCT_LIT_FIELD);
+            }
+            DOTDOT => {
+                p.bump();
+                expr(p);
+            }
+            _ => p.err_and_bump("expected identifier"),
+        }
+        if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+}