Macro patterns are not confused with expressions.

We treat macro calls as expressions (there's appropriate Into impl),
which causes problem if there's expresison and non-expression macro in
the same node (like in the match arm).

We fix this problem by nesting macor patterns into another node (the
same way we nest path into PathExpr or PathPat). Ideally, we probably
should add a similar nesting for macro expressions, but that needs
some careful thinking about macros in blocks: `{ am_i_expression!() }`.

crates/ra_hir_def/src/body/lower.rs

@@ -672,8 +672,7 @@ impl ExprCollector<'_> {
             }
 
             // FIXME: implement
-            ast::Pat::BoxPat(_) => Pat::Missing,
-            ast::Pat::RangePat(_) => Pat::Missing,
+            ast::Pat::BoxPat(_) | ast::Pat::RangePat(_) | ast::Pat::MacroPat(_) => Pat::Missing,
         };
         let ptr = AstPtr::new(&pat);
         self.alloc_pat(pattern, Either::Left(ptr))

crates/ra_hir_ty/src/tests/macros.rs

@@ -1,8 +1,10 @@
-use super::{infer, type_at, type_at_pos};
-use crate::test_db::TestDB;
 use insta::assert_snapshot;
 use ra_db::fixture::WithFixture;
 
+use super::{infer, type_at, type_at_pos};
+
+use crate::test_db::TestDB;
+
 #[test]
 fn cfg_impl_def() {
     let (db, pos) = TestDB::with_position(
@@ -658,3 +660,28 @@ fn test() {
     );
     assert_eq!("S", type_at_pos(&db, pos));
 }
+
+#[test]
+fn macro_in_arm() {
+    assert_snapshot!(
+        infer(r#"
+macro_rules! unit {
+    () => { () };
+}
+
+fn main() {
+    let x = match () {
+        unit!() => 92u32,
+    };
+}
+"#),
+        @r###"
+    [52; 111) '{     ...  }; }': ()
+    [62; 63) 'x': u32
+    [66; 108) 'match ...     }': u32
+    [72; 74) '()': ()
+    [85; 92) 'unit!()': ()
+    [96; 101) '92u32': u32
+    "###
+    );
+}

crates/ra_parser/src/grammar/patterns.rs

@@ -84,7 +84,7 @@ 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]).
             T!['('] | T!['{'] | T![!] => path_or_macro_pat(p),
-            T![:] if p.nth_at(1, T![::]) => path_pat(p),
+            T![:] if p.nth_at(1, T![::]) => path_or_macro_pat(p),
             _ => bind_pat(p, true),
         },
 
@@ -156,7 +156,7 @@ fn path_or_macro_pat(p: &mut Parser) -> CompletedMarker {
         // }
         T![!] => {
             items::macro_call_after_excl(p);
-            MACRO_CALL
+            return m.complete(p, MACRO_CALL).precede(p).complete(p, MACRO_PAT);
         }
         _ => PATH_PAT,
     };

crates/ra_parser/src/syntax_kind/generated.rs

@@ -167,6 +167,7 @@ pub enum SyntaxKind {
     SLICE_PAT,
     RANGE_PAT,
     LITERAL_PAT,
+    MACRO_PAT,
     TUPLE_EXPR,
     ARRAY_EXPR,
     PAREN_EXPR,

crates/ra_syntax/src/ast/generated.rs

@@ -2563,6 +2563,38 @@ impl LiteralPat {
     }
 }
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct MacroPat {
+    pub(crate) syntax: SyntaxNode,
+}
+impl std::fmt::Display for MacroPat {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.syntax(), f)
+    }
+}
+impl AstNode for MacroPat {
+    fn can_cast(kind: SyntaxKind) -> bool {
+        match kind {
+            MACRO_PAT => true,
+            _ => false,
+        }
+    }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode {
+        &self.syntax
+    }
+}
+impl MacroPat {
+    pub fn macro_call(&self) -> Option<MacroCall> {
+        AstChildren::new(&self.syntax).next()
+    }
+}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct RecordPat {
     pub(crate) syntax: SyntaxNode,
 }
@@ -4600,6 +4632,7 @@ pub enum Pat {
     SlicePat(SlicePat),
     RangePat(RangePat),
     LiteralPat(LiteralPat),
+    MacroPat(MacroPat),
 }
 impl From<OrPat> for Pat {
     fn from(node: OrPat) -> Pat {
@@ -4671,6 +4704,11 @@ impl From<LiteralPat> for Pat {
         Pat::LiteralPat(node)
     }
 }
+impl From<MacroPat> for Pat {
+    fn from(node: MacroPat) -> Pat {
+        Pat::MacroPat(node)
+    }
+}
 impl std::fmt::Display for Pat {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
@@ -4681,7 +4719,7 @@ impl AstNode for Pat {
         match kind {
             OR_PAT | PAREN_PAT | REF_PAT | BOX_PAT | BIND_PAT | PLACEHOLDER_PAT | DOT_DOT_PAT
             | PATH_PAT | RECORD_PAT | TUPLE_STRUCT_PAT | TUPLE_PAT | SLICE_PAT | RANGE_PAT
-            | LITERAL_PAT => true,
+            | LITERAL_PAT | MACRO_PAT => true,
             _ => false,
         }
     }
@@ -4701,6 +4739,7 @@ impl AstNode for Pat {
             SLICE_PAT => Pat::SlicePat(SlicePat { syntax }),
             RANGE_PAT => Pat::RangePat(RangePat { syntax }),
             LITERAL_PAT => Pat::LiteralPat(LiteralPat { syntax }),
+            MACRO_PAT => Pat::MacroPat(MacroPat { syntax }),
             _ => return None,
         };
         Some(res)
@@ -4721,6 +4760,7 @@ impl AstNode for Pat {
             Pat::SlicePat(it) => &it.syntax,
             Pat::RangePat(it) => &it.syntax,
             Pat::LiteralPat(it) => &it.syntax,
+            Pat::MacroPat(it) => &it.syntax,
         }
     }
 }

crates/ra_syntax/test_data/parser/inline/ok/0129_marco_pat.txt

@@ -15,6 +15,7 @@ SOURCE_FILE@[0; 33)
         LET_STMT@[16; 30)
           LET_KW@[16; 19) "let"
           WHITESPACE@[19; 20) " "
+          MACRO_PAT@[20; 25)
             MACRO_CALL@[20; 25)
               PATH@[20; 21)
                 PATH_SEGMENT@[20; 21)

xtask/src/ast_src.rs

@@ -138,6 +138,7 @@ pub(crate) const KINDS_SRC: KindsSrc = KindsSrc {
         "SLICE_PAT",
         "RANGE_PAT",
         "LITERAL_PAT",
+        "MACRO_PAT",
         // atoms
         "TUPLE_EXPR",
         "ARRAY_EXPR",
@@ -440,6 +441,7 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
         struct SlicePat { args: [Pat] }
         struct RangePat {}
         struct LiteralPat { Literal }
+        struct MacroPat { MacroCall }
 
         struct RecordPat { RecordFieldPatList, Path }
         struct RecordFieldPatList {
@@ -622,6 +624,7 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
             SlicePat,
             RangePat,
             LiteralPat,
+            MacroPat,
         }
 
         enum AttrInput { Literal, TokenTree }