AST/HIR: Introduce ExprKind::Err for better error recovery in the front-end

petrochenkov · petrochenkov · commit 49f5106447ab · 2018-12-21T01:28:57.000+03:00
diff --git a/src/librustc/cfg/construct.rs b/src/librustc/cfg/construct.rs
@@ -402,7 +402,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
             hir::ExprKind::Closure(..) |
             hir::ExprKind::Lit(..) |
-            hir::ExprKind::Path(_) => {
+            hir::ExprKind::Path(_) |
+            hir::ExprKind::Err => {
                 self.straightline(expr, pred, None::<hir::Expr>.iter())
             }
         }
diff --git a/src/librustc/hir/intravisit.rs b/src/librustc/hir/intravisit.rs
@@ -1109,6 +1109,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
         ExprKind::Yield(ref subexpression) => {
             visitor.visit_expr(subexpression);
         }
+        ExprKind::Err => {}
     }
 }
 
diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
@@ -4127,6 +4127,8 @@ impl<'a> LoweringContext<'a> {
                 hir::ExprKind::Yield(P(expr))
             }
 
+            ExprKind::Err => hir::ExprKind::Err,
+
             // Desugar `ExprIfLet`
             // from: `if let <pat> = <sub_expr> <body> [<else_opt>]`
             ExprKind::IfLet(ref pats, ref sub_expr, ref body, ref else_opt) => {
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
@@ -1372,6 +1372,7 @@ impl Expr {
             ExprKind::Struct(..) => ExprPrecedence::Struct,
             ExprKind::Repeat(..) => ExprPrecedence::Repeat,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
+            ExprKind::Err => ExprPrecedence::Err,
         }
     }
 
@@ -1422,7 +1423,8 @@ impl Expr {
             ExprKind::AddrOf(..) |
             ExprKind::Binary(..) |
             ExprKind::Yield(..) |
-            ExprKind::Cast(..) => {
+            ExprKind::Cast(..) |
+            ExprKind::Err => {
                 false
             }
         }
@@ -1535,6 +1537,9 @@ pub enum ExprKind {
 
     /// A suspension point for generators. This is `yield <expr>` in Rust.
     Yield(P<Expr>),
+
+    /// Placeholder for an expression that wasn't syntactically well formed in some way.
+    Err,
 }
 
 /// Optionally `Self`-qualified value/type path or associated extension.
diff --git a/src/librustc/hir/print.rs b/src/librustc/hir/print.rs
@@ -440,7 +440,9 @@ impl<'a> State<'a> {
                 self.s.word("_")?;
             }
             hir::TyKind::Err => {
-                self.s.word("?")?;
+                self.popen()?;
+                self.s.word("/*ERROR*/")?;
+                self.pclose()?;
             }
         }
         self.end()
@@ -1550,6 +1552,11 @@ impl<'a> State<'a> {
                 self.word_space("yield")?;
                 self.print_expr_maybe_paren(&expr, parser::PREC_JUMP)?;
             }
+            hir::ExprKind::Err => {
+                self.popen()?;
+                self.s.word("/*ERROR*/")?;
+                self.pclose()?;
+            }
         }
         self.ann.post(self, AnnNode::Expr(expr))?;
         self.end()
diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
@@ -602,7 +602,8 @@ impl_stable_hash_for!(enum hir::ExprKind {
     InlineAsm(asm, inputs, outputs),
     Struct(path, fields, base),
     Repeat(val, times),
-    Yield(val)
+    Yield(val),
+    Err
 });
 
 impl_stable_hash_for!(enum hir::LocalSource {
diff --git a/src/librustc/middle/expr_use_visitor.rs b/src/librustc/middle/expr_use_visitor.rs
@@ -489,7 +489,8 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
             }
 
             hir::ExprKind::Continue(..) |
-            hir::ExprKind::Lit(..) => {}
+            hir::ExprKind::Lit(..) |
+            hir::ExprKind::Err => {}
 
             hir::ExprKind::Loop(ref blk, _, _) => {
                 self.walk_block(&blk);
diff --git a/src/librustc/middle/liveness.rs b/src/librustc/middle/liveness.rs
@@ -525,6 +525,7 @@ fn visit_expr<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, expr: &'tcx Expr) {
       hir::ExprKind::Box(..) |
       hir::ExprKind::Yield(..) |
       hir::ExprKind::Type(..) |
+      hir::ExprKind::Err |
       hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
           intravisit::walk_expr(ir, expr);
       }
@@ -1264,7 +1265,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 self.propagate_through_exprs(inputs, succ)
             }
 
-            hir::ExprKind::Lit(..) | hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
+            hir::ExprKind::Lit(..) | hir::ExprKind::Err |
+            hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {
                 succ
             }
 
@@ -1531,7 +1533,7 @@ fn check_expr<'a, 'tcx>(this: &mut Liveness<'a, 'tcx>, expr: &'tcx Expr) {
         hir::ExprKind::Block(..) | hir::ExprKind::AddrOf(..) |
         hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |
         hir::ExprKind::Closure(..) | hir::ExprKind::Path(_) | hir::ExprKind::Yield(..) |
-        hir::ExprKind::Box(..) | hir::ExprKind::Type(..) => {
+        hir::ExprKind::Box(..) | hir::ExprKind::Type(..) | hir::ExprKind::Err => {
             intravisit::walk_expr(this, expr);
         }
     }
diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs
@@ -697,7 +697,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
             hir::ExprKind::Block(..) | hir::ExprKind::Loop(..) | hir::ExprKind::Match(..) |
             hir::ExprKind::Lit(..) | hir::ExprKind::Break(..) |
             hir::ExprKind::Continue(..) | hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |
-            hir::ExprKind::InlineAsm(..) | hir::ExprKind::Box(..) => {
+            hir::ExprKind::InlineAsm(..) | hir::ExprKind::Box(..) | hir::ExprKind::Err => {
                 Ok(self.cat_rvalue_node(expr.hir_id, expr.span, expr_ty))
             }
         }
diff --git a/src/librustc_mir/hair/cx/expr.rs b/src/librustc_mir/hair/cx/expr.rs
@@ -790,6 +790,7 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         hir::ExprKind::Tup(ref fields) => ExprKind::Tuple { fields: fields.to_ref() },
 
         hir::ExprKind::Yield(ref v) => ExprKind::Yield { value: v.to_ref() },
+        hir::ExprKind::Err => unreachable!(),
     };
 
     Expr {
diff --git a/src/librustc_passes/rvalue_promotion.rs b/src/librustc_passes/rvalue_promotion.rs
@@ -459,7 +459,8 @@ fn check_expr_kind<'a, 'tcx>(
             struct_result
         }
 
-        hir::ExprKind::Lit(_) => Promotable,
+        hir::ExprKind::Lit(_) |
+        hir::ExprKind::Err => Promotable,
 
         hir::ExprKind::AddrOf(_, ref expr) |
         hir::ExprKind::Repeat(ref expr, _) => {
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
@@ -4498,6 +4498,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
                 tcx.mk_unit()
             }
+            hir::ExprKind::Err => {
+                tcx.types.err
+            }
         }
     }
 
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
@@ -1011,6 +1011,7 @@ impl Expr {
             ExprKind::Paren(..) => ExprPrecedence::Paren,
             ExprKind::Try(..) => ExprPrecedence::Try,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
+            ExprKind::Err => ExprPrecedence::Err,
         }
     }
 }
@@ -1170,6 +1171,9 @@ pub enum ExprKind {
 
     /// A `yield`, with an optional value to be yielded.
     Yield(Option<P<Expr>>),
+
+    /// Placeholder for an expression that wasn't syntactically well formed in some way.
+    Err,
 }
 
 /// The explicit `Self` type in a "qualified path". The actual
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
@@ -1377,6 +1377,7 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mu
             ExprKind::Yield(ex) => ExprKind::Yield(ex.map(|x| folder.fold_expr(x))),
             ExprKind::Try(ex) => ExprKind::Try(folder.fold_expr(ex)),
             ExprKind::TryBlock(body) => ExprKind::TryBlock(folder.fold_block(body)),
+            ExprKind::Err => ExprKind::Err,
         },
         id: folder.new_id(id),
         span: folder.new_span(span),
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
@@ -1103,7 +1103,9 @@ impl<'a> State<'a> {
                 self.s.word("_")?;
             }
             ast::TyKind::Err => {
-                self.s.word("?")?;
+                self.popen()?;
+                self.s.word("/*ERROR*/")?;
+                self.pclose()?;
             }
             ast::TyKind::ImplicitSelf => {
                 self.s.word("Self")?;
@@ -2401,6 +2403,11 @@ impl<'a> State<'a> {
                 self.s.space()?;
                 self.print_block_with_attrs(blk, attrs)?
             }
+            ast::ExprKind::Err => {
+                self.popen()?;
+                self.s.word("/*ERROR*/")?;
+                self.pclose()?
+            }
         }
         self.ann.post(self, AnnNode::Expr(expr))?;
         self.end()
diff --git a/src/libsyntax/util/parser.rs b/src/libsyntax/util/parser.rs
@@ -276,6 +276,7 @@ pub enum ExprPrecedence {
     TryBlock,
     Struct,
     Async,
+    Err,
 }
 
 impl ExprPrecedence {
@@ -334,7 +335,8 @@ impl ExprPrecedence {
             ExprPrecedence::Block |
             ExprPrecedence::TryBlock |
             ExprPrecedence::Async |
-            ExprPrecedence::Struct => PREC_PAREN,
+            ExprPrecedence::Struct |
+            ExprPrecedence::Err => PREC_PAREN,
         }
     }
 }
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
@@ -812,6 +812,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::TryBlock(ref body) => {
             visitor.visit_block(body)
         }
+        ExprKind::Err => {}
     }
 
     visitor.visit_expr_post(expression)

Original file line number	Diff line number	Diff line change
`@@ -402,7 +402,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {`
`402`	`402`
`403`	`403`	`hir::ExprKind::Closure(..) \|`
`404`	`404`	`hir::ExprKind::Lit(..) \|`
`405`		`- hir::ExprKind::Path(_) => {`
	`405`	`+ hir::ExprKind::Path(_) \|`
	`406`	`+ hir::ExprKind::Err => {`
`406`	`407`	`self.straightline(expr, pred, None::<hir::Expr>.iter())`
`407`	`408`	`}`
`408`	`409`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1109,6 +1109,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {`
`1109`	`1109`	`ExprKind::Yield(ref subexpression) => {`
`1110`	`1110`	`visitor.visit_expr(subexpression);`
`1111`	`1111`	`}`
	`1112`	`+ ExprKind::Err => {}`
`1112`	`1113`	`}`
`1113`	`1114`	`}`
`1114`	`1115`
Original file line number	Diff line number	Diff line change
`@@ -4127,6 +4127,8 @@ impl<'a> LoweringContext<'a> {`
`4127`	`4127`	`hir::ExprKind::Yield(P(expr))`
`4128`	`4128`	`}`
`4129`	`4129`
	`4130`	`+ ExprKind::Err => hir::ExprKind::Err,`
	`4131`	`+`
`4130`	`4132`	// Desugar `ExprIfLet`
`4131`	`4133`	// from: `if let <pat> = <sub_expr> <body> [<else_opt>]`
`4132`	`4134`	`ExprKind::IfLet(ref pats, ref sub_expr, ref body, ref else_opt) => {`
Original file line number	Diff line number	Diff line change
`@@ -1372,6 +1372,7 @@ impl Expr {`
`1372`	`1372`	`ExprKind::Struct(..) => ExprPrecedence::Struct,`
`1373`	`1373`	`ExprKind::Repeat(..) => ExprPrecedence::Repeat,`
`1374`	`1374`	`ExprKind::Yield(..) => ExprPrecedence::Yield,`
	`1375`	`+ ExprKind::Err => ExprPrecedence::Err,`
`1375`	`1376`	`}`
`1376`	`1377`	`}`
`1377`	`1378`
`@@ -1422,7 +1423,8 @@ impl Expr {`
`1422`	`1423`	`ExprKind::AddrOf(..) \|`
`1423`	`1424`	`ExprKind::Binary(..) \|`
`1424`	`1425`	`ExprKind::Yield(..) \|`
`1425`		`- ExprKind::Cast(..) => {`
	`1426`	`+ ExprKind::Cast(..) \|`
	`1427`	`+ ExprKind::Err => {`
`1426`	`1428`	`false`
`1427`	`1429`	`}`
`1428`	`1430`	`}`
`@@ -1535,6 +1537,9 @@ pub enum ExprKind {`
`1535`	`1537`
`1536`	`1538`	/// A suspension point for generators. This is `yield <expr>` in Rust.
`1537`	`1539`	`Yield(P<Expr>),`
	`1540`	`+`
	`1541`	`+ /// Placeholder for an expression that wasn't syntactically well formed in some way.`
	`1542`	`+ Err,`
`1538`	`1543`	`}`
`1539`	`1544`
`1540`	`1545`	/// Optionally `Self`-qualified value/type path or associated extension.
Original file line number	Diff line number	Diff line change
`@@ -440,7 +440,9 @@ impl<'a> State<'a> {`
`440`	`440`	`self.s.word("_")?;`
`441`	`441`	`}`
`442`	`442`	`hir::TyKind::Err => {`
`443`		`- self.s.word("?")?;`
	`443`	`+ self.popen()?;`
	`444`	`+ self.s.word("/ERROR/")?;`
	`445`	`+ self.pclose()?;`
`444`	`446`	`}`
`445`	`447`	`}`
`446`	`448`	`self.end()`
`@@ -1550,6 +1552,11 @@ impl<'a> State<'a> {`
`1550`	`1552`	`self.word_space("yield")?;`
`1551`	`1553`	`self.print_expr_maybe_paren(&expr, parser::PREC_JUMP)?;`
`1552`	`1554`	`}`
	`1555`	`+ hir::ExprKind::Err => {`
	`1556`	`+ self.popen()?;`
	`1557`	`+ self.s.word("/ERROR/")?;`
	`1558`	`+ self.pclose()?;`
	`1559`	`+ }`
`1553`	`1560`	`}`
`1554`	`1561`	`self.ann.post(self, AnnNode::Expr(expr))?;`
`1555`	`1562`	`self.end()`
Original file line number	Diff line number	Diff line change
`@@ -489,7 +489,8 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {`
`489`	`489`	`}`
`490`	`490`
`491`	`491`	`hir::ExprKind::Continue(..) \|`
`492`		`- hir::ExprKind::Lit(..) => {}`
	`492`	`+ hir::ExprKind::Lit(..) \|`
	`493`	`+ hir::ExprKind::Err => {}`
`493`	`494`
`494`	`495`	`hir::ExprKind::Loop(ref blk, _, _) => {`
`495`	`496`	`self.walk_block(&blk);`
Original file line number	Diff line number	Diff line change
`@@ -525,6 +525,7 @@ fn visit_expr<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, expr: &'tcx Expr) {`
`525`	`525`	`hir::ExprKind::Box(..) \|`
`526`	`526`	`hir::ExprKind::Yield(..) \|`
`527`	`527`	`hir::ExprKind::Type(..) \|`
	`528`	`+ hir::ExprKind::Err \|`
`528`	`529`	`hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
`529`	`530`	`intravisit::walk_expr(ir, expr);`
`530`	`531`	`}`
`@@ -1264,7 +1265,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {`
`1264`	`1265`	`self.propagate_through_exprs(inputs, succ)`
`1265`	`1266`	`}`
`1266`	`1267`
`1267`		`- hir::ExprKind::Lit(..) \| hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
	`1268`	`+ hir::ExprKind::Lit(..) \| hir::ExprKind::Err \|`
	`1269`	`+ hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
`1268`	`1270`	`succ`
`1269`	`1271`	`}`
`1270`	`1272`
`@@ -1531,7 +1533,7 @@ fn check_expr<'a, 'tcx>(this: &mut Liveness<'a, 'tcx>, expr: &'tcx Expr) {`
`1531`	`1533`	`hir::ExprKind::Block(..) \| hir::ExprKind::AddrOf(..) \|`
`1532`	`1534`	`hir::ExprKind::Struct(..) \| hir::ExprKind::Repeat(..) \|`
`1533`	`1535`	`hir::ExprKind::Closure(..) \| hir::ExprKind::Path(_) \| hir::ExprKind::Yield(..) \|`
`1534`		`- hir::ExprKind::Box(..) \| hir::ExprKind::Type(..) => {`
	`1536`	`+ hir::ExprKind::Box(..) \| hir::ExprKind::Type(..) \| hir::ExprKind::Err => {`
`1535`	`1537`	`intravisit::walk_expr(this, expr);`
`1536`	`1538`	`}`
`1537`	`1539`	`}`
Original file line number	Diff line number	Diff line change
`@@ -697,7 +697,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {`
`697`	`697`	`hir::ExprKind::Block(..) \| hir::ExprKind::Loop(..) \| hir::ExprKind::Match(..) \|`
`698`	`698`	`hir::ExprKind::Lit(..) \| hir::ExprKind::Break(..) \|`
`699`	`699`	`hir::ExprKind::Continue(..) \| hir::ExprKind::Struct(..) \| hir::ExprKind::Repeat(..) \|`
`700`		`- hir::ExprKind::InlineAsm(..) \| hir::ExprKind::Box(..) => {`
	`700`	`+ hir::ExprKind::InlineAsm(..) \| hir::ExprKind::Box(..) \| hir::ExprKind::Err => {`
`701`	`701`	`Ok(self.cat_rvalue_node(expr.hir_id, expr.span, expr_ty))`
`702`	`702`	`}`
`703`	`703`	`}`