From 1126bbb82ab2f81dcb33df696a1bb601a98d3174 Mon Sep 17 00:00:00 2001 From: Rob Findley Date: Mon, 22 Feb 2021 15:39:00 -0500 Subject: [PATCH] go/parser: return ast.BadExpr for missing index operands The parser was returning the indexed operand when a slice or index or instance expression was missing any index arguments (as in the expression `a[]`). This can result in returning an *ast.Ident for the LHS of the (invalid) assignment `a[] = ...` -- in this case parsing the LHS as just `a`. Unfortunately, as the indexed operand `a` has already been resolved, this results in a panic for duplicate resolution. Fix this by instead returning an ast.BadExpr. This can suppress some subsequent errors from the typechecker, but those errors may or may not be correct anyway. Other interpretations, such as an *ast.IndexExpr with bad or missing X, run into potential misinterpretations downstream (both caused errors in go/types and/or gopls). Fixes #44504 Change-Id: I5ca8bed4a1861bcc7db8898770b08937110981d4 Reviewed-on: https://go-review.googlesource.com/c/go/+/295151 Trust: Robert Findley Run-TryBot: Robert Findley TryBot-Result: Go Bot Reviewed-by: Robert Griesemer --- src/go/parser/parser.go | 3 ++- src/go/parser/testdata/issue44504.src | 13 +++++++++++++ src/go/types/fixedbugs/issue39634.go2 | 2 +- 3 files changed, 16 insertions(+), 2 deletions(-) create mode 100644 src/go/parser/testdata/issue44504.src diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go index 41c3f2943e..5c4cea8638 100644 --- a/src/go/parser/parser.go +++ b/src/go/parser/parser.go @@ -1485,8 +1485,9 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr { // empty index, slice or index expressions are not permitted; // accept them for parsing tolerance, but complain p.errorExpected(p.pos, "operand") + rbrack := p.pos p.next() - return x + return &ast.BadExpr{From: x.Pos(), To: rbrack} } p.exprLev++ diff --git a/src/go/parser/testdata/issue44504.src b/src/go/parser/testdata/issue44504.src new file mode 100644 index 0000000000..7791f4a809 --- /dev/null +++ b/src/go/parser/testdata/issue44504.src @@ -0,0 +1,13 @@ +// Copyright 2021 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. + +// Test case for issue 44504: panic due to duplicate resolution of slice/index +// operands. We should not try to resolve a LHS expression with invalid syntax. + +package p + +func _() { + var items []bool + items[] /* ERROR "operand" */ = false +} diff --git a/src/go/types/fixedbugs/issue39634.go2 b/src/go/types/fixedbugs/issue39634.go2 index 249542d541..78dee00383 100644 --- a/src/go/types/fixedbugs/issue39634.go2 +++ b/src/go/types/fixedbugs/issue39634.go2 @@ -84,7 +84,7 @@ var x T25 /* ERROR without instantiation */ .m1 // crash 26 type T26 = interface{ F26[ /* ERROR methods cannot have type parameters */ Z any]() } -func F26[Z any]() T26 { return F26 /* ERROR without instantiation */ /* ERROR missing method */ [] /* ERROR operand */ } +func F26[Z any]() T26 { return F26[] /* ERROR operand */ } // crash 27 func e27[T any]() interface{ x27 /* ERROR not a type */ }