From c65a2781be7a8029435ea3d6a3c54c601ac4ba3e Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Thu, 29 Mar 2018 18:22:23 -0700 Subject: [PATCH] cmd/compile: better handling of incorrect type switches Don't report errors if we don't have a correct type switch guard; instead ignore it and leave it to the type-checker to report the error. This leads to better error messages concentrating on the type switch guard rather than errors around (confusing) syntactic details. Also clean up some code setting up AssertExpr (they never have a nil Type field) and remove some incorrect TODOs. Fixes #24470. Change-Id: I69512f36e0417e3b5ea9c8856768e04b19d654a8 Reviewed-on: https://go-review.googlesource.com/103615 Run-TryBot: Robert Griesemer TryBot-Result: Gobot Gobot Reviewed-by: Matthew Dempsky --- src/cmd/compile/internal/gc/noder.go | 8 +-- src/cmd/compile/internal/syntax/nodes.go | 18 +++--- src/cmd/compile/internal/syntax/parser.go | 75 +++++++++------------- src/cmd/compile/internal/syntax/printer.go | 18 ++---- test/fixedbugs/issue24470.go | 15 +++++ test/syntax/typesw.go | 2 +- 6 files changed, 62 insertions(+), 74 deletions(-) create mode 100644 test/fixedbugs/issue24470.go diff --git a/src/cmd/compile/internal/gc/noder.go b/src/cmd/compile/internal/gc/noder.go index e2f60c1a8d..9947f248be 100644 --- a/src/cmd/compile/internal/gc/noder.go +++ b/src/cmd/compile/internal/gc/noder.go @@ -598,13 +598,7 @@ func (p *noder) expr(expr syntax.Expr) *Node { n.SetSliceBounds(index[0], index[1], index[2]) return n case *syntax.AssertExpr: - if expr.Type == nil { - panic("unexpected AssertExpr") - } - // TODO(mdempsky): parser.pexpr uses p.expr(), but - // seems like the type field should be parsed with - // ntype? Shrug, doesn't matter here. - return p.nod(expr, ODOTTYPE, p.expr(expr.X), p.expr(expr.Type)) + return p.nod(expr, ODOTTYPE, p.expr(expr.X), p.typeExpr(expr.Type)) case *syntax.Operation: if expr.Op == syntax.Add && expr.Y != nil { return p.sum(expr) diff --git a/src/cmd/compile/internal/syntax/nodes.go b/src/cmd/compile/internal/syntax/nodes.go index 8df9fd5c4e..c1da4adf52 100644 --- a/src/cmd/compile/internal/syntax/nodes.go +++ b/src/cmd/compile/internal/syntax/nodes.go @@ -198,12 +198,19 @@ type ( // X.(Type) AssertExpr struct { - X Expr - // TODO(gri) consider using Name{"..."} instead of nil (permits attaching of comments) + X Expr Type Expr expr } + // X.(type) + // Lhs := X.(type) + TypeSwitchGuard struct { + Lhs *Name // nil means no Lhs := + X Expr // X.(type) + expr + } + Operation struct { Op Operator X, Y Expr // Y == nil means unary expression @@ -413,13 +420,6 @@ type ( simpleStmt } - TypeSwitchGuard struct { - // TODO(gri) consider using Name{"..."} instead of nil (permits attaching of comments) - Lhs *Name // nil means no Lhs := - X Expr // X.(type) - expr - } - CaseClause struct { Cases Expr // nil means default clause Body []Stmt diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go index db0fb39c8c..68d09ef697 100644 --- a/src/cmd/compile/internal/syntax/parser.go +++ b/src/cmd/compile/internal/syntax/parser.go @@ -907,6 +907,7 @@ loop: p.next() if p.got(_Type) { t := new(TypeSwitchGuard) + // t.Lhs is filled in by parser.simpleStmt t.pos = pos t.X = x x = t @@ -914,7 +915,7 @@ loop: t := new(AssertExpr) t.pos = pos t.X = x - t.Type = p.expr() + t.Type = p.type_() x = t } p.want(_Rparen) @@ -1584,12 +1585,12 @@ func (p *parser) bad() *BadExpr { var ImplicitOne = &BasicLit{Value: "1"} // SimpleStmt = EmptyStmt | ExpressionStmt | SendStmt | IncDecStmt | Assignment | ShortVarDecl . -func (p *parser) simpleStmt(lhs Expr, rangeOk bool) SimpleStmt { +func (p *parser) simpleStmt(lhs Expr, keyword token) SimpleStmt { if trace { defer p.trace("simpleStmt")() } - if rangeOk && p.tok == _Range { + if keyword == _For && p.tok == _Range { // _Range expr if debug && lhs != nil { panic("invalid call of simpleStmt") @@ -1636,51 +1637,35 @@ func (p *parser) simpleStmt(lhs Expr, rangeOk bool) SimpleStmt { } // expr_list - pos := p.pos() switch p.tok { - case _Assign: + case _Assign, _Define: + pos := p.pos() + var op Operator + if p.tok == _Define { + op = Def + } p.next() - if rangeOk && p.tok == _Range { - // expr_list '=' _Range expr - return p.newRangeClause(lhs, false) + if keyword == _For && p.tok == _Range { + // expr_list op= _Range expr + return p.newRangeClause(lhs, op == Def) } - // expr_list '=' expr_list - return p.newAssignStmt(pos, 0, lhs, p.exprList()) - - case _Define: - p.next() - - if rangeOk && p.tok == _Range { - // expr_list ':=' range expr - return p.newRangeClause(lhs, true) - } - - // expr_list ':=' expr_list + // expr_list op= expr_list rhs := p.exprList() - if x, ok := rhs.(*TypeSwitchGuard); ok { - switch lhs := lhs.(type) { - case *Name: + if x, ok := rhs.(*TypeSwitchGuard); ok && keyword == _Switch && op == Def { + if lhs, ok := lhs.(*Name); ok { + // switch … lhs := rhs.(type) x.Lhs = lhs - case *ListExpr: - p.errorAt(lhs.Pos(), fmt.Sprintf("cannot assign 1 value to %d variables", len(lhs.ElemList))) - // make the best of what we have - if lhs, ok := lhs.ElemList[0].(*Name); ok { - x.Lhs = lhs - } - default: - p.errorAt(lhs.Pos(), fmt.Sprintf("invalid variable name %s in type switch", String(lhs))) + s := new(ExprStmt) + s.pos = x.Pos() + s.X = x + return s } - s := new(ExprStmt) - s.pos = x.Pos() - s.X = x - return s } - as := p.newAssignStmt(pos, Def, lhs, rhs) - return as + return p.newAssignStmt(pos, op, lhs, rhs) default: p.syntaxError("expecting := or = or comma") @@ -1820,7 +1805,7 @@ func (p *parser) header(keyword token) (init SimpleStmt, cond Expr, post SimpleS if p.got(_Var) { p.syntaxError(fmt.Sprintf("var declaration not allowed in %s initializer", keyword.String())) } - init = p.simpleStmt(nil, keyword == _For) + init = p.simpleStmt(nil, keyword) // If we have a range clause, we are done (can only happen for keyword == _For). if _, ok := init.(*RangeClause); ok { p.xnest = outer @@ -1847,17 +1832,17 @@ func (p *parser) header(keyword token) (init SimpleStmt, cond Expr, post SimpleS p.syntaxError("expecting for loop condition") goto done } - condStmt = p.simpleStmt(nil, false) + condStmt = p.simpleStmt(nil, 0 /* range not permitted */) } p.want(_Semi) if p.tok != _Lbrace { - post = p.simpleStmt(nil, false) + post = p.simpleStmt(nil, 0 /* range not permitted */) if a, _ := post.(*AssignStmt); a != nil && a.Op == Def { p.syntaxErrorAt(a.Pos(), "cannot declare in post statement of for loop") } } } else if p.tok != _Lbrace { - condStmt = p.simpleStmt(nil, false) + condStmt = p.simpleStmt(nil, keyword) } } else { condStmt = init @@ -2003,7 +1988,7 @@ func (p *parser) commClause() *CommClause { switch p.tok { case _Case: p.next() - c.Comm = p.simpleStmt(nil, false) + c.Comm = p.simpleStmt(nil, 0) // The syntax restricts the possible simple statements here to: // @@ -2049,7 +2034,7 @@ func (p *parser) stmtOrNil() Stmt { if label, ok := lhs.(*Name); ok && p.tok == _Colon { return p.labeledStmtOrNil(label) } - return p.simpleStmt(lhs, false) + return p.simpleStmt(lhs, 0) } switch p.tok { @@ -2068,13 +2053,13 @@ func (p *parser) stmtOrNil() Stmt { case _Operator, _Star: switch p.op { case Add, Sub, Mul, And, Xor, Not: - return p.simpleStmt(nil, false) // unary operators + return p.simpleStmt(nil, 0) // unary operators } case _Literal, _Func, _Lparen, // operands _Lbrack, _Struct, _Map, _Chan, _Interface, // composite types _Arrow: // receive operator - return p.simpleStmt(nil, false) + return p.simpleStmt(nil, 0) case _For: return p.forStmt() diff --git a/src/cmd/compile/internal/syntax/printer.go b/src/cmd/compile/internal/syntax/printer.go index f4c2b6dde6..8ff3bfa794 100644 --- a/src/cmd/compile/internal/syntax/printer.go +++ b/src/cmd/compile/internal/syntax/printer.go @@ -393,13 +393,13 @@ func (p *printer) printRawNode(n Node) { p.print(_Rbrack) case *AssertExpr: - p.print(n.X, _Dot, _Lparen) - if n.Type != nil { - p.printNode(n.Type) - } else { - p.print(_Type) + p.print(n.X, _Dot, _Lparen, n.Type, _Rparen) + + case *TypeSwitchGuard: + if n.Lhs != nil { + p.print(n.Lhs, blank, _Define, blank) } - p.print(_Rparen) + p.print(n.X, _Dot, _Lparen, _Type, _Rparen) case *CallExpr: p.print(n.Fun, _Lparen) @@ -557,12 +557,6 @@ func (p *printer) printRawNode(n Node) { } p.printSwitchBody(n.Body) - case *TypeSwitchGuard: - if n.Lhs != nil { - p.print(n.Lhs, blank, _Define, blank) - } - p.print(n.X, _Dot, _Lparen, _Type, _Rparen) - case *SelectStmt: p.print(_Select, blank) // for now p.printSelectBody(n.Body) diff --git a/test/fixedbugs/issue24470.go b/test/fixedbugs/issue24470.go new file mode 100644 index 0000000000..d0e5e23fa9 --- /dev/null +++ b/test/fixedbugs/issue24470.go @@ -0,0 +1,15 @@ +// errorcheck + +// Copyright 2018 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Verify that we get "use of .(type) outside type switch" +// before any other (misleading) errors. Test case from issue. + +package p + +func f(i interface{}) { + if x, ok := i.(type); ok { // ERROR "outside type switch" + } +} diff --git a/test/syntax/typesw.go b/test/syntax/typesw.go index 8d89860d11..f9120e8851 100644 --- a/test/syntax/typesw.go +++ b/test/syntax/typesw.go @@ -7,7 +7,7 @@ package main func main() { - switch main() := interface{}(nil).(type) { // ERROR "invalid variable name" + switch main() := interface{}(nil).(type) { // ERROR "invalid variable name|used as value" default: } }