From 2c94c4964aa6242098f97ca3421a750a763567b4 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Wed, 23 Dec 2020 02:15:30 +0100
Subject: Parse const effect block

---
 crates/parser/src/grammar/expressions/atom.rs      |  9 +++++++++
 crates/parser/src/grammar/items.rs                 |  7 +++++--
 .../parser/inline/ok/0157_const_block.rast         | 23 ++++++++++++++++++++++
 .../test_data/parser/inline/ok/0157_const_block.rs |  1 +
 4 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 crates/syntax/test_data/parser/inline/ok/0157_const_block.rast
 create mode 100644 crates/syntax/test_data/parser/inline/ok/0157_const_block.rs

diff --git a/crates/parser/src/grammar/expressions/atom.rs b/crates/parser/src/grammar/expressions/atom.rs
index e897d5a52..c7a3556a7 100644
--- a/crates/parser/src/grammar/expressions/atom.rs
+++ b/crates/parser/src/grammar/expressions/atom.rs
@@ -46,6 +46,7 @@ pub(super) const ATOM_EXPR_FIRST: TokenSet =
         T![continue],
         T![async],
         T![try],
+        T![const],
         T![loop],
         T![for],
         LIFETIME_IDENT,
@@ -115,6 +116,14 @@ pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<(CompletedMar
             block_expr(p);
             m.complete(p, EFFECT_EXPR)
         }
+        // test const_block
+        // fn f() { const { } }
+        T![const] if la == T!['{'] => {
+            let m = p.start();
+            p.bump(T![const]);
+            block_expr(p);
+            m.complete(p, EFFECT_EXPR)
+        }
         T!['{'] => {
             // test for_range_from
             // fn foo() {
diff --git a/crates/parser/src/grammar/items.rs b/crates/parser/src/grammar/items.rs
index 8999829b4..72b73f891 100644
--- a/crates/parser/src/grammar/items.rs
+++ b/crates/parser/src/grammar/items.rs
@@ -96,7 +96,10 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
     let mut has_mods = false;
 
     // modifiers
-    has_mods |= p.eat(T![const]);
+    if p.at(T![const]) && p.nth(1) != T!['{'] {
+        p.eat(T![const]);
+        has_mods = true;
+    }
 
     // test_err async_without_semicolon
     // fn foo() { let _ = async {} }
@@ -167,7 +170,7 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             m.complete(p, TRAIT);
         }
 
-        T![const] => {
+        T![const] if p.nth(1) != T!['{'] => {
             consts::konst(p, m);
         }
 
diff --git a/crates/syntax/test_data/parser/inline/ok/0157_const_block.rast b/crates/syntax/test_data/parser/inline/ok/0157_const_block.rast
new file mode 100644
index 000000000..d5d2c8fe3
--- /dev/null
+++ b/crates/syntax/test_data/parser/inline/ok/0157_const_block.rast
@@ -0,0 +1,23 @@
+SOURCE_FILE@0..21
+  FN@0..20
+    FN_KW@0..2 "fn"
+    WHITESPACE@2..3 " "
+    NAME@3..4
+      IDENT@3..4 "f"
+    PARAM_LIST@4..6
+      L_PAREN@4..5 "("
+      R_PAREN@5..6 ")"
+    WHITESPACE@6..7 " "
+    BLOCK_EXPR@7..20
+      L_CURLY@7..8 "{"
+      WHITESPACE@8..9 " "
+      EFFECT_EXPR@9..18
+        CONST_KW@9..14 "const"
+        WHITESPACE@14..15 " "
+        BLOCK_EXPR@15..18
+          L_CURLY@15..16 "{"
+          WHITESPACE@16..17 " "
+          R_CURLY@17..18 "}"
+      WHITESPACE@18..19 " "
+      R_CURLY@19..20 "}"
+  WHITESPACE@20..21 "\n"
diff --git a/crates/syntax/test_data/parser/inline/ok/0157_const_block.rs b/crates/syntax/test_data/parser/inline/ok/0157_const_block.rs
new file mode 100644
index 000000000..a2e3565a3
--- /dev/null
+++ b/crates/syntax/test_data/parser/inline/ok/0157_const_block.rs
@@ -0,0 +1 @@
+fn f() { const { } }
-- 
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