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cmd/compile/internal/syntax: better error message for missing type constraint

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For #43527.

Change-Id: I8c706e68572286d5675383eb2dfd75b5618b646b
Reviewed-on: https://go-review.googlesource.com/c/go/+/348730
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
This commit is contained in:
Robert Griesemer 2021-09-08 21:30:01 -07:00
parent e1c3f2158f
commit 73483df406
4 changed files with 44 additions and 11 deletions
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22
src/cmd/compile/internal/syntax/parser.go
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@ -1908,8 +1908,9 @@ func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*
defer p.trace("paramList")()
}
var named int // number of parameters that have an explicit name and type/bound
p.list(_Comma, close, func() bool {
var named int // number of parameters that have an explicit name and type
var typed int // number of parameters that have an explicit type
end := p.list(_Comma, close, func() bool {
par := p.paramDeclOrNil(name)
name = nil // 1st name was consumed if present
if par != nil {
@ -1919,6 +1920,9 @@ func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*
if par.Name != nil && par.Type != nil {
named++
}
if par.Type != nil {
typed++
}
list = append(list, par)
}
return false
@ -1939,10 +1943,11 @@ func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*
}
} else if named != len(list) {
// some named => all must have names and types
var pos Pos // left-most error position (or unknown)
var typ Expr
var pos Pos // left-most error position (or unknown)
var typ Expr // current type (from right to left)
for i := len(list) - 1; i >= 0; i-- {
if par := list[i]; par.Type != nil {
par := list[i]
if par.Type != nil {
typ = par.Type
if par.Name == nil {
pos = typ.Pos()
@ -1961,7 +1966,12 @@ func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*
if pos.IsKnown() {
var msg string
if requireNames {
msg = "type parameters must be named"
if named == typed {
pos = end // position error at closing ]
msg = "missing type constraint"
} else {
msg = "type parameters must be named"
}
} else {
msg = "mixed named and unnamed parameters"
}