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[dev.typeparams] go/parser: error for type instances without ParseTypeParams

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It should be an invariant that the parser does not produce ast.CallExprs
with Brackets == true unless parsing with ParseTypeParams.

Fix the one case where this invariant was violated, and add a test for
errors produced in valid generic code when ParseTypeParams is unset. We
did have some coverage of errors in short_test.go, but I find them to be
easier to read in a testdata file and would like to gradually migrate
them there.

Change-Id: If2d174377087daa1b820cabc2b5bf8bcb0b39d8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/284192
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
This commit is contained in:
Rob Findley 2021-01-15 11:08:02 -05:00 committed by Robert Findley
parent 90bfc73071
commit 958927c824
2 changed files with 24 additions and 0 deletions
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7
src/go/parser/parser.go
View File

@ -1494,6 +1494,7 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
var args []ast.Expr
var index [N]ast.Expr
var colons [N - 1]token.Pos
var firstComma token.Pos
if p.tok != token.COLON {
// We can't know if we have an index expression or a type instantiation;
// so even if we see a (named) type we are not going to be in type context.
@ -1512,6 +1513,7 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
}
}
case token.COMMA:
firstComma = p.pos
// instance expression
args = append(args, index[0])
for p.tok == token.COMMA {
@ -1549,6 +1551,11 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
return &ast.IndexExpr{X: x, Lbrack: lbrack, Index: index[0], Rbrack: rbrack}
}
if p.mode&ParseTypeParams == 0 {
p.error(firstComma, "expected ']' or ':', found ','")
return &ast.BadExpr{From: args[0].Pos(), To: args[len(args)-1].End()}
}
// instance expression
return &ast.CallExpr{Fun: x, Lparen: lbrack, Args: args, Rparen: rbrack, Brackets: true}
}

17
src/go/parser/testdata/typeparams.src vendored Normal file
View File

@ -0,0 +1,17 @@
// 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 cases for error messages produced while parsing code that uses type
// parameters, without ParseTypeParams being enabled.
package p
type List[E any /* ERROR "expected ']', found any" */ ] []E
type Pair[L, /* ERROR "expected ']', found ','" */ R any] struct {
Left L
Right R
}
var _ = Pair[int, /* ERROR "expected ']' or ':', found ','" */ string]{}