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

petrochenkov · petrochenkov · commit a5c52c72ae3c · 2018-12-27T15:51:36.000+03:00
diff --git a/src/librustc/cfg/construct.rs b/src/librustc/cfg/construct.rs
@@ -392,7 +392,8 @@ 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
@@ -1099,6 +1099,7 @@ 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
@@ -4117,6 +4117,8 @@ 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
@@ -1362,6 +1362,7 @@ impl Expr {
             ExprKind::Struct(..) => ExprPrecedence::Struct,
             ExprKind::Repeat(..) => ExprPrecedence::Repeat,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
+            ExprKind::Err => ExprPrecedence::Err,
         }
     }
 
@@ -1412,7 +1413,8 @@ impl Expr {
             ExprKind::AddrOf(..) |
             ExprKind::Binary(..) |
             ExprKind::Yield(..) |
-            ExprKind::Cast(..) => {
+            ExprKind::Cast(..) |
+            ExprKind::Err => {
                 false
             }
         }
@@ -1525,6 +1527,9 @@ 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
@@ -430,7 +430,9 @@ impl<'a> State<'a> {
                 self.s.word("_")?;
             }
             hir::TyKind::Err => {
-                self.s.word("?")?;
+                self.popen()?;
+                self.s.word("/*ERROR*/")?;
+                self.pclose()?;
             }
         }
         self.end()
@@ -1540,6 +1542,11 @@ 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
@@ -592,7 +592,8 @@ 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
@@ -479,7 +479,8 @@ 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
@@ -515,6 +515,7 @@ 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);
       }
@@ -1254,7 +1255,8 @@ 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
             }
 
@@ -1521,7 +1523,7 @@ 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
@@ -687,7 +687,7 @@ 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
@@ -780,6 +780,7 @@ 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
@@ -449,7 +449,8 @@ 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
@@ -4513,6 +4513,9 @@ 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
@@ -1001,6 +1001,7 @@ impl Expr {
             ExprKind::Paren(..) => ExprPrecedence::Paren,
             ExprKind::Try(..) => ExprPrecedence::Try,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
+            ExprKind::Err => ExprPrecedence::Err,
         }
     }
 }
@@ -1160,6 +1161,9 @@ 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
@@ -1367,6 +1367,7 @@ 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
@@ -1093,7 +1093,9 @@ 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")?;
@@ -2391,6 +2393,11 @@ 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
@@ -267,6 +267,7 @@ pub enum ExprPrecedence {
     TryBlock,
     Struct,
     Async,
+    Err,
 }
 
 impl ExprPrecedence {
@@ -325,7 +326,8 @@ 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
@@ -802,6 +802,7 @@ 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
`@@ -392,7 +392,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {`
`392`	`392`
`393`	`393`	`hir::ExprKind::Closure(..) \|`
`394`	`394`	`hir::ExprKind::Lit(..) \|`
`395`		`- hir::ExprKind::Path(_) => {`
	`395`	`+ hir::ExprKind::Path(_) \|`
	`396`	`+ hir::ExprKind::Err => {`
`396`	`397`	`self.straightline(expr, pred, None::<hir::Expr>.iter())`
`397`	`398`	`}`
`398`	`399`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1099,6 +1099,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {`
`1099`	`1099`	`ExprKind::Yield(ref subexpression) => {`
`1100`	`1100`	`visitor.visit_expr(subexpression);`
`1101`	`1101`	`}`
	`1102`	`+ ExprKind::Err => {}`
`1102`	`1103`	`}`
`1103`	`1104`	`}`
`1104`	`1105`
Original file line number	Diff line number	Diff line change
`@@ -4117,6 +4117,8 @@ impl<'a> LoweringContext<'a> {`
`4117`	`4117`	`hir::ExprKind::Yield(P(expr))`
`4118`	`4118`	`}`
`4119`	`4119`
	`4120`	`+ ExprKind::Err => hir::ExprKind::Err,`
	`4121`	`+`
`4120`	`4122`	// Desugar `ExprIfLet`
`4121`	`4123`	// from: `if let <pat> = <sub_expr> <body> [<else_opt>]`
`4122`	`4124`	`ExprKind::IfLet(ref pats, ref sub_expr, ref body, ref else_opt) => {`
Original file line number	Diff line number	Diff line change
`@@ -1362,6 +1362,7 @@ impl Expr {`
`1362`	`1362`	`ExprKind::Struct(..) => ExprPrecedence::Struct,`
`1363`	`1363`	`ExprKind::Repeat(..) => ExprPrecedence::Repeat,`
`1364`	`1364`	`ExprKind::Yield(..) => ExprPrecedence::Yield,`
	`1365`	`+ ExprKind::Err => ExprPrecedence::Err,`
`1365`	`1366`	`}`
`1366`	`1367`	`}`
`1367`	`1368`
`@@ -1412,7 +1413,8 @@ impl Expr {`
`1412`	`1413`	`ExprKind::AddrOf(..) \|`
`1413`	`1414`	`ExprKind::Binary(..) \|`
`1414`	`1415`	`ExprKind::Yield(..) \|`
`1415`		`- ExprKind::Cast(..) => {`
	`1416`	`+ ExprKind::Cast(..) \|`
	`1417`	`+ ExprKind::Err => {`
`1416`	`1418`	`false`
`1417`	`1419`	`}`
`1418`	`1420`	`}`
`@@ -1525,6 +1527,9 @@ pub enum ExprKind {`
`1525`	`1527`
`1526`	`1528`	/// A suspension point for generators. This is `yield <expr>` in Rust.
`1527`	`1529`	`Yield(P<Expr>),`
	`1530`	`+`
	`1531`	`+ /// Placeholder for an expression that wasn't syntactically well formed in some way.`
	`1532`	`+ Err,`
`1528`	`1533`	`}`
`1529`	`1534`
`1530`	`1535`	/// Optionally `Self`-qualified value/type path or associated extension.
Original file line number	Diff line number	Diff line change
`@@ -430,7 +430,9 @@ impl<'a> State<'a> {`
`430`	`430`	`self.s.word("_")?;`
`431`	`431`	`}`
`432`	`432`	`hir::TyKind::Err => {`
`433`		`- self.s.word("?")?;`
	`433`	`+ self.popen()?;`
	`434`	`+ self.s.word("/ERROR/")?;`
	`435`	`+ self.pclose()?;`
`434`	`436`	`}`
`435`	`437`	`}`
`436`	`438`	`self.end()`
`@@ -1540,6 +1542,11 @@ impl<'a> State<'a> {`
`1540`	`1542`	`self.word_space("yield")?;`
`1541`	`1543`	`self.print_expr_maybe_paren(&expr, parser::PREC_JUMP)?;`
`1542`	`1544`	`}`
	`1545`	`+ hir::ExprKind::Err => {`
	`1546`	`+ self.popen()?;`
	`1547`	`+ self.s.word("/ERROR/")?;`
	`1548`	`+ self.pclose()?;`
	`1549`	`+ }`
`1543`	`1550`	`}`
`1544`	`1551`	`self.ann.post(self, AnnNode::Expr(expr))?;`
`1545`	`1552`	`self.end()`
Original file line number	Diff line number	Diff line change
`@@ -479,7 +479,8 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {`
`479`	`479`	`}`
`480`	`480`
`481`	`481`	`hir::ExprKind::Continue(..) \|`
`482`		`- hir::ExprKind::Lit(..) => {}`
	`482`	`+ hir::ExprKind::Lit(..) \|`
	`483`	`+ hir::ExprKind::Err => {}`
`483`	`484`
`484`	`485`	`hir::ExprKind::Loop(ref blk, _, _) => {`
`485`	`486`	`self.walk_block(&blk);`
Original file line number	Diff line number	Diff line change
`@@ -515,6 +515,7 @@ fn visit_expr<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, expr: &'tcx Expr) {`
`515`	`515`	`hir::ExprKind::Box(..) \|`
`516`	`516`	`hir::ExprKind::Yield(..) \|`
`517`	`517`	`hir::ExprKind::Type(..) \|`
	`518`	`+ hir::ExprKind::Err \|`
`518`	`519`	`hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
`519`	`520`	`intravisit::walk_expr(ir, expr);`
`520`	`521`	`}`
`@@ -1254,7 +1255,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {`
`1254`	`1255`	`self.propagate_through_exprs(inputs, succ)`
`1255`	`1256`	`}`
`1256`	`1257`
`1257`		`- hir::ExprKind::Lit(..) \| hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
	`1258`	`+ hir::ExprKind::Lit(..) \| hir::ExprKind::Err \|`
	`1259`	`+ hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => {`
`1258`	`1260`	`succ`
`1259`	`1261`	`}`
`1260`	`1262`
`@@ -1521,7 +1523,7 @@ fn check_expr<'a, 'tcx>(this: &mut Liveness<'a, 'tcx>, expr: &'tcx Expr) {`
`1521`	`1523`	`hir::ExprKind::Block(..) \| hir::ExprKind::AddrOf(..) \|`
`1522`	`1524`	`hir::ExprKind::Struct(..) \| hir::ExprKind::Repeat(..) \|`
`1523`	`1525`	`hir::ExprKind::Closure(..) \| hir::ExprKind::Path(_) \| hir::ExprKind::Yield(..) \|`
`1524`		`- hir::ExprKind::Box(..) \| hir::ExprKind::Type(..) => {`
	`1526`	`+ hir::ExprKind::Box(..) \| hir::ExprKind::Type(..) \| hir::ExprKind::Err => {`
`1525`	`1527`	`intravisit::walk_expr(this, expr);`
`1526`	`1528`	`}`
`1527`	`1529`	`}`
Original file line number	Diff line number	Diff line change
`@@ -687,7 +687,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {`
`687`	`687`	`hir::ExprKind::Block(..) \| hir::ExprKind::Loop(..) \| hir::ExprKind::Match(..) \|`
`688`	`688`	`hir::ExprKind::Lit(..) \| hir::ExprKind::Break(..) \|`
`689`	`689`	`hir::ExprKind::Continue(..) \| hir::ExprKind::Struct(..) \| hir::ExprKind::Repeat(..) \|`
`690`		`- hir::ExprKind::InlineAsm(..) \| hir::ExprKind::Box(..) => {`
	`690`	`+ hir::ExprKind::InlineAsm(..) \| hir::ExprKind::Box(..) \| hir::ExprKind::Err => {`
`691`	`691`	`Ok(self.cat_rvalue_node(expr.hir_id, expr.span, expr_ty))`
`692`	`692`	`}`
`693`	`693`	`}`