Enable parsing of attributes inside a match block

We allow invalid inner attributes to be parsed, e.g. inner attributes that are
not directly after the opening brace of the match block.

Instead we run validation on `MatchArmList` to allow better reporting of errors.

crates/ra_syntax/src/ast.rs

@@ -153,6 +153,20 @@ impl FnDef {
 }
 
 impl Attr {
+    pub fn is_inner(&self) -> bool {
+        let tt = match self.value() {
+            None => return false,
+            Some(tt) => tt,
+        };
+
+        let prev = match tt.syntax().prev_sibling() {
+            None => return false,
+            Some(prev) => prev,
+        };
+
+        prev.kind() == EXCL
+    }
+
     pub fn as_atom(&self) -> Option<SmolStr> {
         let tt = self.value()?;
         let (_bra, attr, _ket) = tt.syntax().children().collect_tuple()?;

crates/ra_syntax/src/ast/generated.rs

@@ -1946,6 +1946,7 @@ impl ToOwned for MatchArm {
 }
 
 
+impl ast::AttrsOwner for MatchArm {}
 impl MatchArm {
     pub fn pats(&self) -> impl Iterator<Item = &Pat> {
         super::children(self)
@@ -1986,6 +1987,7 @@ impl ToOwned for MatchArmList {
 }
 
 
+impl ast::AttrsOwner for MatchArmList {}
 impl MatchArmList {
     pub fn arms(&self) -> impl Iterator<Item = &MatchArm> {
         super::children(self)

crates/ra_syntax/src/grammar.ron

@@ -413,13 +413,15 @@ Grammar(
         ),
         "MatchArmList": (
             collections: [ ["arms", "MatchArm"] ],
+            traits: [ "AttrsOwner" ]
         ),
         "MatchArm": (
             options: [
                 [ "guard", "MatchGuard" ],
                 "Expr",
             ],
-            collections: [ [ "pats", "Pat" ] ]
+            collections: [ [ "pats", "Pat" ] ],
+            traits: [ "AttrsOwner" ]
         ),
         "MatchGuard": (options: ["Expr"]),
         "StructLit": (options: ["Path", "NamedFieldList", ["spread", "Expr"]]),

crates/ra_syntax/src/grammar/attributes.rs

@@ -1,5 +1,15 @@
 use super::*;
 
+/// Parses both inner & outer attributes.
+///
+/// Allowing to run validation for reporting errors
+/// regarding attributes
+pub(super) fn all_attributes(p: &mut Parser) {
+    while p.at(POUND) {
+        attribute(p, p.nth(1) == EXCL)
+    }
+}
+
 pub(super) fn inner_attributes(p: &mut Parser) {
     while p.current() == POUND && p.nth(1) == EXCL {
         attribute(p, true)

crates/ra_syntax/src/grammar/expressions/atom.rs

@@ -313,11 +313,44 @@ pub(crate) fn match_arm_list(p: &mut Parser) {
     assert!(p.at(L_CURLY));
     let m = p.start();
     p.eat(L_CURLY);
+
+    // test match_arms_inner_attribute
+    // fn foo() {
+    //     match () {
+    //         #![doc("Inner attribute")]
+    //         #![doc("Can be")]
+    //         #![doc("Stacked")]
+    //         _ => (),
+    //     }
+    // }
+    attributes::inner_attributes(p);
+
     while !p.at(EOF) && !p.at(R_CURLY) {
         if p.at(L_CURLY) {
             error_block(p, "expected match arm");
             continue;
         }
+
+        // This may result in invalid attributes
+        // if there are inner attributes mixed in together
+        // with the outer attributes, but we allow parsing
+        // those so we can run validation and report better errors
+
+        // test match_arms_outer_attributes
+        // fn foo() {
+        //     match () {
+        //         #[cfg(feature = "some")]
+        //         _ => (),
+        //         #[cfg(feature = "other")]
+        //         _ => (),
+        //         #[cfg(feature = "many")]
+        //         #[cfg(feature = "attributes")]
+        //         #[cfg(feature = "before")]
+        //         _ => (),
+        //     }
+        // }
+        attributes::all_attributes(p);
+
         // test match_arms_commas
         // fn foo() {
         //     match () {

crates/ra_syntax/src/syntax_node/syntax_error.rs

@@ -92,6 +92,7 @@ pub enum SyntaxErrorKind {
     UnclosedString,
     InvalidSuffix,
     InvalidBlockAttr,
+    InvalidMatchInnerAttr,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -136,6 +137,9 @@ impl fmt::Display for SyntaxErrorKind {
             InvalidBlockAttr => {
                 write!(f, "A block in this position cannot accept inner attributes")
             }
+            InvalidMatchInnerAttr => {
+                write!(f, "Inner attributes are only allowed directly after the opening brace of the match expression")
+            }
             ParseError(msg) => write!(f, "{}", msg.0),
         }
     }

crates/ra_syntax/src/validation.rs

@@ -3,6 +3,7 @@ mod byte_string;
 mod char;
 mod string;
 mod block;
+mod match_armlist;
 
 use crate::{
     SourceFile, syntax_node::SyntaxError, AstNode,
@@ -19,6 +20,7 @@ pub(crate) fn validate(file: &SourceFile) -> Vec<SyntaxError> {
             .visit::<ast::Char, _>(self::char::validate_char_node)
             .visit::<ast::String, _>(self::string::validate_string_node)
             .visit::<ast::Block, _>(self::block::validate_block_node)
+            .visit::<ast::MatchArmList, _>(self::match_armlist::validate_match_armlist)
             .accept(node);
     }
     errors

crates/ra_syntax/src/validation/match_armlist.rs

@@ -0,0 +1,28 @@
+use crate::{
+    ast::{self, AttrsOwner, AstNode},
+    syntax_node::{
+        SyntaxError,
+        SyntaxErrorKind::*,
+        Direction,
+    },
+};
+
+pub(crate) fn validate_match_armlist(node: &ast::MatchArmList, errors: &mut Vec<SyntaxError>) {
+    // Report errors for any inner attribute
+    // which has a preceding matcharm or an outer attribute
+    for inner_attr in node.attrs().filter(|s| s.is_inner()) {
+        let any_errors = inner_attr.syntax().siblings(Direction::Prev).any(|s| {
+            match (ast::MatchArm::cast(s), ast::Attr::cast(s)) {
+                (Some(_), _) => true,
+                // Outer attributes which preceed an inner attribute are not allowed
+                (_, Some(a)) if !a.is_inner() => true,
+                (_, Some(_)) => false,
+                (None, None) => false,
+            }
+        });
+
+        if any_errors {
+            errors.push(SyntaxError::new(InvalidMatchInnerAttr, inner_attr.syntax().range()));
+        }
+    }
+}