10 files changed, 182 insertions, 139 deletions

diff --git a/crates/ra_syntax/src/ast.rs b/crates/ra_syntax/src/ast.rs
index 521ca8ab8..1876afe95 100644
--- a/crates/ra_syntax/src/ast.rs
+++ b/crates/ra_syntax/src/ast.rs
@@ -16,9 +16,7 @@ use crate::{
 };
 
 pub use self::{
-    expr_extensions::{
-        ArrayExprKind, BinOp, BlockModifier, ElseBranch, LiteralKind, PrefixOp, RangeOp,
-    },
+    expr_extensions::{ArrayExprKind, BinOp, Effect, ElseBranch, LiteralKind, PrefixOp, RangeOp},
     extensions::{
         AttrKind, FieldKind, NameOrNameRef, PathSegmentKind, SelfParamKind, SlicePatComponents,
         StructKind, TypeBoundKind, VisibilityKind,
diff --git a/crates/ra_syntax/src/ast/edit.rs b/crates/ra_syntax/src/ast/edit.rs
index 26e4576ff..c507dc683 100644
--- a/crates/ra_syntax/src/ast/edit.rs
+++ b/crates/ra_syntax/src/ast/edit.rs
@@ -28,7 +28,7 @@ impl ast::BinExpr {
 
 impl ast::FnDef {
     #[must_use]
-    pub fn with_body(&self, body: ast::Block) -> ast::FnDef {
+    pub fn with_body(&self, body: ast::BlockExpr) -> ast::FnDef {
         let mut to_insert: ArrayVec<[SyntaxElement; 2]> = ArrayVec::new();
         let old_body_or_semi: SyntaxElement = if let Some(old_body) = self.body() {
             old_body.syntax().clone().into()
diff --git a/crates/ra_syntax/src/ast/expr_extensions.rs b/crates/ra_syntax/src/ast/expr_extensions.rs
index 352c0d2c5..7771d6759 100644
--- a/crates/ra_syntax/src/ast/expr_extensions.rs
+++ b/crates/ra_syntax/src/ast/expr_extensions.rs
@@ -16,7 +16,7 @@ impl ast::Expr {
             | ast::Expr::WhileExpr(_)
             | ast::Expr::BlockExpr(_)
             | ast::Expr::MatchExpr(_)
-            | ast::Expr::TryExpr(_) => true,
+            | ast::Expr::EffectExpr(_) => true,
             _ => false,
         }
     }
@@ -43,7 +43,7 @@ impl ast::IfExpr {
         Some(res)
     }
 
-    fn blocks(&self) -> AstChildren<ast::BlockExpr> {
+    pub fn blocks(&self) -> AstChildren<ast::BlockExpr> {
         support::children(self.syntax())
     }
 }
@@ -359,22 +359,34 @@ impl ast::Literal {
     }
 }
 
-pub enum BlockModifier {
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Effect {
     Async(SyntaxToken),
     Unsafe(SyntaxToken),
+    Try(SyntaxToken),
+    // Very much not an effect, but we stuff it into this node anyway
+    Label(ast::Label),
 }
 
-impl ast::BlockExpr {
-    pub fn modifier(&self) -> Option<BlockModifier> {
+impl ast::EffectExpr {
+    pub fn effect(&self) -> Effect {
         if let Some(token) = self.async_token() {
-            return Some(BlockModifier::Async(token));
+            return Effect::Async(token);
         }
         if let Some(token) = self.unsafe_token() {
-            return Some(BlockModifier::Unsafe(token));
+            return Effect::Unsafe(token);
+        }
+        if let Some(token) = self.try_token() {
+            return Effect::Try(token);
+        }
+        if let Some(label) = self.label() {
+            return Effect::Label(label);
         }
-        None
+        unreachable!("ast::EffectExpr without Effect")
     }
+}
 
+impl ast::BlockExpr {
     /// false if the block is an intrinsic part of the syntax and can't be
     /// replaced with arbitrary expression.
     ///
@@ -383,15 +395,12 @@ impl ast::BlockExpr {
     /// const FOO: () = { stand_alone };
     /// ```
     pub fn is_standalone(&self) -> bool {
-        if self.modifier().is_some() {
-            return false;
-        }
         let parent = match self.syntax().parent() {
             Some(it) => it,
             None => return true,
         };
         match parent.kind() {
-            FN_DEF | IF_EXPR | WHILE_EXPR | LOOP_EXPR => false,
+            FN_DEF | IF_EXPR | WHILE_EXPR | LOOP_EXPR | EFFECT_EXPR => false,
             _ => true,
         }
     }
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index 45e3dd2d3..98c38d009 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -423,6 +423,10 @@ impl ast::MacroCall {
             None
         }
     }
+
+    pub fn is_bang(&self) -> bool {
+        self.is_macro_rules().is_none()
+    }
 }
 
 impl ast::LifetimeParam {
@@ -463,7 +467,7 @@ impl ast::TokenTree {
 
     pub fn right_delimiter_token(&self) -> Option<SyntaxToken> {
         self.syntax().last_child_or_token()?.into_token().filter(|it| match it.kind() {
-            T!['{'] | T!['('] | T!['['] => true,
+            T!['}'] | T![')'] | T![']'] => true,
             _ => false,
         })
     }
diff --git a/crates/ra_syntax/src/ast/generated/nodes.rs b/crates/ra_syntax/src/ast/generated/nodes.rs
index 81260680f..c2cc25958 100644
--- a/crates/ra_syntax/src/ast/generated/nodes.rs
+++ b/crates/ra_syntax/src/ast/generated/nodes.rs
@@ -12,6 +12,7 @@ pub struct SourceFile {
 }
 impl ast::ModuleItemOwner for SourceFile {}
 impl ast::AttrsOwner for SourceFile {}
+impl ast::DocCommentsOwner for SourceFile {}
 impl SourceFile {
     pub fn modules(&self) -> AstChildren<Module> { support::children(&self.syntax) }
 }
@@ -259,6 +260,7 @@ pub struct ImplDef {
 }
 impl ast::TypeParamsOwner for ImplDef {}
 impl ast::AttrsOwner for ImplDef {}
+impl ast::DocCommentsOwner for ImplDef {}
 impl ImplDef {
     pub fn default_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![default]) }
     pub fn const_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![const]) }
@@ -476,6 +478,19 @@ impl LoopExpr {
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct EffectExpr {
+    pub(crate) syntax: SyntaxNode,
+}
+impl ast::AttrsOwner for EffectExpr {}
+impl EffectExpr {
+    pub fn label(&self) -> Option<Label> { support::child(&self.syntax) }
+    pub fn try_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![try]) }
+    pub fn unsafe_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![unsafe]) }
+    pub fn async_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![async]) }
+    pub fn block_expr(&self) -> Option<BlockExpr> { support::child(&self.syntax) }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct ForExpr {
     pub(crate) syntax: SyntaxNode,
 }
@@ -541,11 +556,12 @@ pub struct BlockExpr {
     pub(crate) syntax: SyntaxNode,
 }
 impl ast::AttrsOwner for BlockExpr {}
+impl ast::ModuleItemOwner for BlockExpr {}
 impl BlockExpr {
-    pub fn label(&self) -> Option<Label> { support::child(&self.syntax) }
-    pub fn unsafe_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![unsafe]) }
-    pub fn async_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![async]) }
-    pub fn block(&self) -> Option<Block> { support::child(&self.syntax) }
+    pub fn l_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['{']) }
+    pub fn statements(&self) -> AstChildren<Stmt> { support::children(&self.syntax) }
+    pub fn expr(&self) -> Option<Expr> { support::child(&self.syntax) }
+    pub fn r_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['}']) }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -617,8 +633,8 @@ pub struct TryExpr {
 }
 impl ast::AttrsOwner for TryExpr {}
 impl TryExpr {
-    pub fn try_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![try]) }
     pub fn expr(&self) -> Option<Expr> { support::child(&self.syntax) }
+    pub fn question_mark_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![?]) }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -1112,19 +1128,6 @@ impl Condition {
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct Block {
-    pub(crate) syntax: SyntaxNode,
-}
-impl ast::AttrsOwner for Block {}
-impl ast::ModuleItemOwner for Block {}
-impl Block {
-    pub fn l_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['{']) }
-    pub fn statements(&self) -> AstChildren<Stmt> { support::children(&self.syntax) }
-    pub fn expr(&self) -> Option<Expr> { support::child(&self.syntax) }
-    pub fn r_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['}']) }
-}
-
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct ParamList {
     pub(crate) syntax: SyntaxNode,
 }
@@ -1241,6 +1244,8 @@ pub struct PathSegment {
 impl PathSegment {
     pub fn coloncolon_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![::]) }
     pub fn crate_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![crate]) }
+    pub fn self_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![self]) }
+    pub fn super_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![super]) }
     pub fn l_angle_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![<]) }
     pub fn name_ref(&self) -> Option<NameRef> { support::child(&self.syntax) }
     pub fn type_arg_list(&self) -> Option<TypeArgList> { support::child(&self.syntax) }
@@ -1465,6 +1470,7 @@ pub enum Expr {
     FieldExpr(FieldExpr),
     AwaitExpr(AwaitExpr),
     TryExpr(TryExpr),
+    EffectExpr(EffectExpr),
     CastExpr(CastExpr),
     RefExpr(RefExpr),
     PrefixExpr(PrefixExpr),
@@ -1947,6 +1953,17 @@ impl AstNode for LoopExpr {
     }
     fn syntax(&self) -> &SyntaxNode { &self.syntax }
 }
+impl AstNode for EffectExpr {
+    fn can_cast(kind: SyntaxKind) -> bool { kind == EFFECT_EXPR }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+}
 impl AstNode for ForExpr {
     fn can_cast(kind: SyntaxKind) -> bool { kind == FOR_EXPR }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
@@ -2629,17 +2646,6 @@ impl AstNode for Condition {
     }
     fn syntax(&self) -> &SyntaxNode { &self.syntax }
 }
-impl AstNode for Block {
-    fn can_cast(kind: SyntaxKind) -> bool { kind == BLOCK }
-    fn cast(syntax: SyntaxNode) -> Option<Self> {
-        if Self::can_cast(syntax.kind()) {
-            Some(Self { syntax })
-        } else {
-            None
-        }
-    }
-    fn syntax(&self) -> &SyntaxNode { &self.syntax }
-}
 impl AstNode for ParamList {
     fn can_cast(kind: SyntaxKind) -> bool { kind == PARAM_LIST }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
@@ -3288,6 +3294,9 @@ impl From<AwaitExpr> for Expr {
 impl From<TryExpr> for Expr {
     fn from(node: TryExpr) -> Expr { Expr::TryExpr(node) }
 }
+impl From<EffectExpr> for Expr {
+    fn from(node: EffectExpr) -> Expr { Expr::EffectExpr(node) }
+}
 impl From<CastExpr> for Expr {
     fn from(node: CastExpr) -> Expr { Expr::CastExpr(node) }
 }
@@ -3318,8 +3327,10 @@ impl AstNode for Expr {
             TUPLE_EXPR | ARRAY_EXPR | PAREN_EXPR | PATH_EXPR | LAMBDA_EXPR | IF_EXPR
             | LOOP_EXPR | FOR_EXPR | WHILE_EXPR | CONTINUE_EXPR | BREAK_EXPR | LABEL
             | BLOCK_EXPR | RETURN_EXPR | MATCH_EXPR | RECORD_LIT | CALL_EXPR | INDEX_EXPR
-            | METHOD_CALL_EXPR | FIELD_EXPR | AWAIT_EXPR | TRY_EXPR | CAST_EXPR | REF_EXPR
-            | PREFIX_EXPR | RANGE_EXPR | BIN_EXPR | LITERAL | MACRO_CALL | BOX_EXPR => true,
+            | METHOD_CALL_EXPR | FIELD_EXPR | AWAIT_EXPR | TRY_EXPR | EFFECT_EXPR | CAST_EXPR
+            | REF_EXPR | PREFIX_EXPR | RANGE_EXPR | BIN_EXPR | LITERAL | MACRO_CALL | BOX_EXPR => {
+                true
+            }
             _ => false,
         }
     }
@@ -3347,6 +3358,7 @@ impl AstNode for Expr {
             FIELD_EXPR => Expr::FieldExpr(FieldExpr { syntax }),
             AWAIT_EXPR => Expr::AwaitExpr(AwaitExpr { syntax }),
             TRY_EXPR => Expr::TryExpr(TryExpr { syntax }),
+            EFFECT_EXPR => Expr::EffectExpr(EffectExpr { syntax }),
             CAST_EXPR => Expr::CastExpr(CastExpr { syntax }),
             REF_EXPR => Expr::RefExpr(RefExpr { syntax }),
             PREFIX_EXPR => Expr::PrefixExpr(PrefixExpr { syntax }),
@@ -3383,6 +3395,7 @@ impl AstNode for Expr {
             Expr::FieldExpr(it) => &it.syntax,
             Expr::AwaitExpr(it) => &it.syntax,
             Expr::TryExpr(it) => &it.syntax,
+            Expr::EffectExpr(it) => &it.syntax,
             Expr::CastExpr(it) => &it.syntax,
             Expr::RefExpr(it) => &it.syntax,
             Expr::PrefixExpr(it) => &it.syntax,
@@ -3863,6 +3876,11 @@ impl std::fmt::Display for LoopExpr {
         std::fmt::Display::fmt(self.syntax(), f)
     }
 }
+impl std::fmt::Display for EffectExpr {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        std::fmt::Display::fmt(self.syntax(), f)
+    }
+}
 impl std::fmt::Display for ForExpr {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
@@ -4173,11 +4191,6 @@ impl std::fmt::Display for Condition {
         std::fmt::Display::fmt(self.syntax(), f)
     }
 }
-impl std::fmt::Display for Block {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        std::fmt::Display::fmt(self.syntax(), f)
-    }
-}
 impl std::fmt::Display for ParamList {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         std::fmt::Display::fmt(self.syntax(), f)
diff --git a/crates/ra_syntax/src/ast/make.rs b/crates/ra_syntax/src/ast/make.rs
index 492088353..7b17fef49 100644
--- a/crates/ra_syntax/src/ast/make.rs
+++ b/crates/ra_syntax/src/ast/make.rs
@@ -82,14 +82,6 @@ pub fn block_expr(
     ast_from_text(&format!("fn f() {}", buf))
 }
 
-pub fn block_from_expr(e: ast::Expr) -> ast::Block {
-    return from_text(&format!("{{ {} }}", e));
-
-    fn from_text(text: &str) -> ast::Block {
-        ast_from_text(&format!("fn f() {}", text))
-    }
-}
-
 pub fn expr_unit() -> ast::Expr {
     expr_from_text("()")
 }
diff --git a/crates/ra_syntax/src/lib.rs b/crates/ra_syntax/src/lib.rs
index ceeb2bde9..d0234cada 100644
--- a/crates/ra_syntax/src/lib.rs
+++ b/crates/ra_syntax/src/lib.rs
@@ -237,8 +237,7 @@ fn api_walkthrough() {
 
     // Let's get the `1 + 1` expression!
     let body: ast::BlockExpr = func.body().unwrap();
-    let block = body.block().unwrap();
-    let expr: ast::Expr = block.expr().unwrap();
+    let expr: ast::Expr = body.expr().unwrap();
 
     // Enums are used to group related ast nodes together, and can be used for
     // matching. However, because there are no public fields, it's possible to
@@ -274,8 +273,8 @@ fn api_walkthrough() {
     assert_eq!(text.to_string(), "1 + 1");
 
     // There's a bunch of traversal methods on `SyntaxNode`:
-    assert_eq!(expr_syntax.parent().as_ref(), Some(block.syntax()));
-    assert_eq!(block.syntax().first_child_or_token().map(|it| it.kind()), Some(T!['{']));
+    assert_eq!(expr_syntax.parent().as_ref(), Some(body.syntax()));
+    assert_eq!(body.syntax().first_child_or_token().map(|it| it.kind()), Some(T!['{']));
     assert_eq!(
         expr_syntax.next_sibling_or_token().map(|it| it.kind()),
         Some(SyntaxKind::WHITESPACE)
diff --git a/crates/ra_syntax/src/parsing/lexer.rs b/crates/ra_syntax/src/parsing/lexer.rs
index f450ef4a2..1a5a6dc06 100644
--- a/crates/ra_syntax/src/parsing/lexer.rs
+++ b/crates/ra_syntax/src/parsing/lexer.rs
@@ -180,7 +180,7 @@ fn rustc_token_kind_to_syntax_kind(
     return (syntax_kind, None);
 
     fn match_literal_kind(kind: &rustc_lexer::LiteralKind) -> (SyntaxKind, Option<&'static str>) {
-        use rustc_lexer::LiteralKind as LK;
+        use rustc_lexer::{LexRawStrError, LiteralKind as LK};
 
         #[rustfmt::skip]
         let syntax_kind = match *kind {
@@ -215,21 +215,28 @@ fn rustc_token_kind_to_syntax_kind(
                 return (BYTE_STRING, Some("Missing trailing `\"` symbol to terminate the byte string literal"))
             }
 
-            LK::RawStr { started: true, terminated: true, .. } => RAW_STRING,
-            LK::RawStr { started: true, terminated: false, .. } => {
-                return (RAW_STRING, Some("Missing trailing `\"` with `#` symbols to terminate the raw string literal"))
-            }
-            LK::RawStr { started: false, .. } => {
-                return (RAW_STRING, Some("Missing `\"` symbol after `#` symbols to begin the raw string literal"))
-            }
+            LK::RawStr(str) => match str.validate() {
+                Ok(_) => RAW_STRING,
+                Err(LexRawStrError::InvalidStarter) => return (RAW_STRING, Some("Missing `\"` symbol after `#` symbols to begin the raw string literal")),
+                Err(LexRawStrError::NoTerminator { expected, found, .. }) => if expected == found {
+                    return (RAW_STRING, Some("Missing trailing `\"` to terminate the raw string literal"))
+                } else {
+                    return (RAW_STRING, Some("Missing trailing `\"` with `#` symbols to terminate the raw string literal"))
+
+                },
+                Err(LexRawStrError::TooManyDelimiters { .. }) => return (RAW_STRING, Some("Too many `#` symbols: raw strings may be delimited by up to 65535 `#` symbols")),
+            },
+            LK::RawByteStr(str) => match str.validate() {
+                Ok(_) => RAW_BYTE_STRING,
+                Err(LexRawStrError::InvalidStarter) => return (RAW_BYTE_STRING, Some("Missing `\"` symbol after `#` symbols to begin the raw byte string literal")),
+                Err(LexRawStrError::NoTerminator { expected, found, .. }) => if expected == found {
+                    return (RAW_BYTE_STRING, Some("Missing trailing `\"` to terminate the raw byte string literal"))
+                } else {
+                    return (RAW_BYTE_STRING, Some("Missing trailing `\"` with `#` symbols to terminate the raw byte string literal"))
 
-            LK::RawByteStr { started: true, terminated: true, .. } => RAW_BYTE_STRING,
-            LK::RawByteStr { started: true, terminated: false, .. } => {
-                return (RAW_BYTE_STRING, Some("Missing trailing `\"` with `#` symbols to terminate the raw byte string literal"))
-            }
-            LK::RawByteStr { started: false, .. } => {
-                return (RAW_BYTE_STRING, Some("Missing `\"` symbol after `#` symbols to begin the raw byte string literal"))
-            }
+                },
+                Err(LexRawStrError::TooManyDelimiters { .. }) => return (RAW_BYTE_STRING, Some("Too many `#` symbols: raw byte strings may be delimited by up to 65535 `#` symbols")),
+            },
         };
 
         (syntax_kind, None)
diff --git a/crates/ra_syntax/src/validation.rs b/crates/ra_syntax/src/validation.rs
index f0b3dec63..e075cd801 100644
--- a/crates/ra_syntax/src/validation.rs
+++ b/crates/ra_syntax/src/validation.rs
@@ -96,7 +96,7 @@ pub(crate) fn validate(root: &SyntaxNode) -> Vec<SyntaxError> {
                 ast::RecordField(it) => validate_numeric_name(it.name_ref(), &mut errors),
                 ast::Visibility(it) => validate_visibility(it, &mut errors),
                 ast::RangeExpr(it) => validate_range_expr(it, &mut errors),
-                ast::PathSegment(it) => validate_crate_keyword_in_path_segment(it, &mut errors),
+                ast::PathSegment(it) => validate_path_keywords(it, &mut errors),
                 _ => (),
             }
         }
@@ -224,59 +224,82 @@ fn validate_range_expr(expr: ast::RangeExpr, errors: &mut Vec<SyntaxError>) {
     }
 }
 
-fn validate_crate_keyword_in_path_segment(
-    segment: ast::PathSegment,
-    errors: &mut Vec<SyntaxError>,
-) {
-    const ERR_MSG: &str = "The `crate` keyword is only allowed as the first segment of a path";
+fn validate_path_keywords(segment: ast::PathSegment, errors: &mut Vec<SyntaxError>) {
+    use ast::PathSegmentKind;
 
-    let crate_token = match segment.crate_token() {
-        None => return,
-        Some(it) => it,
-    };
+    let path = segment.parent_path();
+    let is_path_start = segment.coloncolon_token().is_none() && path.qualifier().is_none();
+
+    if let Some(token) = segment.self_token() {
+        if !is_path_start {
+            errors.push(SyntaxError::new(
+                "The `self` keyword is only allowed as the first segment of a path",
+                token.text_range(),
+            ));
+        }
+    } else if let Some(token) = segment.crate_token() {
+        if !is_path_start || use_prefix(path).is_some() {
+            errors.push(SyntaxError::new(
+                "The `crate` keyword is only allowed as the first segment of a path",
+                token.text_range(),
+            ));
+        }
+    } else if let Some(token) = segment.super_token() {
+        if !all_supers(&path) {
+            errors.push(SyntaxError::new(
+                "The `super` keyword may only be preceded by other `super`s",
+                token.text_range(),
+            ));
+            return;
+        }
 
-    // Disallow both ::crate and foo::crate
-    let mut path = segment.parent_path();
-    if segment.coloncolon_token().is_some() || path.qualifier().is_some() {
-        errors.push(SyntaxError::new(ERR_MSG, crate_token.text_range()));
-        return;
+        let mut curr_path = path;
+        while let Some(prefix) = use_prefix(curr_path) {
+            if !all_supers(&prefix) {
+                errors.push(SyntaxError::new(
+                    "The `super` keyword may only be preceded by other `super`s",
+                    token.text_range(),
+                ));
+                return;
+            }
+            curr_path = prefix;
+        }
     }
 
-    // For expressions and types, validation is complete, but we still have
-    // to handle invalid UseItems like this:
-    //
-    //      use foo:{crate::bar::baz};
-    //
-    // To handle this we must inspect the parent `UseItem`s and `UseTree`s
-    // but right now we're looking deep inside the nested `Path` nodes because
-    // `Path`s are left-associative:
-    //
-    //   ((crate)::bar)::baz)
-    //       ^ current value of path
-    //
-    // So we need to climb to the top
-    while let Some(parent) = path.parent_path() {
-        path = parent;
+    fn use_prefix(mut path: ast::Path) -> Option<ast::Path> {
+        for node in path.syntax().ancestors().skip(1) {
+            match_ast! {
+                match node {
+                    ast::UseTree(it) => if let Some(tree_path) = it.path() {
+                        // Even a top-level path exists within a `UseTree` so we must explicitly
+                        // allow our path but disallow anything else
+                        if tree_path != path {
+                            return Some(tree_path);
+                        }
+                    },
+                    ast::UseTreeList(_it) => continue,
+                    ast::Path(parent) => path = parent,
+                    _ => return None,
+                }
+            };
+        }
+        return None;
     }
 
-    // Now that we've found the whole path we need to see if there's a prefix
-    // somewhere in the UseTree hierarchy. This check is arbitrarily deep
-    // because rust allows arbitrary nesting like so:
-    //
-    // use {foo::{{{{crate::bar::baz}}}}};
-    for node in path.syntax().ancestors().skip(1) {
-        match_ast! {
-            match node {
-                ast::UseTree(it) => if let Some(tree_path) = it.path() {
-                    // Even a top-level path exists within a `UseTree` so we must explicitly
-                    // allow our path but disallow anything else
-                    if tree_path != path {
-                        errors.push(SyntaxError::new(ERR_MSG, crate_token.text_range()));
-                    }
-                },
-                ast::UseTreeList(_it) => continue,
-                _ => return,
-            }
+    fn all_supers(path: &ast::Path) -> bool {
+        let segment = match path.segment() {
+            Some(it) => it,
+            None => return false,
         };
+
+        if segment.kind() != Some(PathSegmentKind::SuperKw) {
+            return false;
+        }
+
+        if let Some(ref subpath) = path.qualifier() {
+            return all_supers(subpath);
+        }
+
+        return true;
     }
 }
diff --git a/crates/ra_syntax/src/validation/block.rs b/crates/ra_syntax/src/validation/block.rs
index 8e962ab5b..2c08f7e6e 100644
--- a/crates/ra_syntax/src/validation/block.rs
+++ b/crates/ra_syntax/src/validation/block.rs
@@ -6,19 +6,17 @@ use crate::{
     SyntaxKind::*,
 };
 
-pub(crate) fn validate_block_expr(expr: ast::BlockExpr, errors: &mut Vec<SyntaxError>) {
-    if let Some(parent) = expr.syntax().parent() {
+pub(crate) fn validate_block_expr(block: ast::BlockExpr, errors: &mut Vec<SyntaxError>) {
+    if let Some(parent) = block.syntax().parent() {
         match parent.kind() {
-            FN_DEF | EXPR_STMT | BLOCK => return,
+            FN_DEF | EXPR_STMT | BLOCK_EXPR => return,
             _ => {}
         }
     }
-    if let Some(block) = expr.block() {
-        errors.extend(block.attrs().map(|attr| {
-            SyntaxError::new(
-                "A block in this position cannot accept inner attributes",
-                attr.syntax().text_range(),
-            )
-        }))
-    }
+    errors.extend(block.attrs().map(|attr| {
+        SyntaxError::new(
+            "A block in this position cannot accept inner attributes",
+            attr.syntax().text_range(),
+        )
+    }))
 }