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x/tools/cmd/eg: embedded fields are mishandled #10252

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josharian opened this issue Mar 25, 2015 · 3 comments
Open

x/tools/cmd/eg: embedded fields are mishandled #10252

josharian opened this issue Mar 25, 2015 · 3 comments
Milestone
Unreleased

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@josharian
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$GOPATH/src/egbug/x.go:

package egbug

type T struct {
    *E
    E2 *E
}

type E struct {
    Next *T
}

func main() {
    var t *T
    t.Next = new(T)
}

Template:

package p

import "egbug"

func before(t *egbug.T) *egbug.T { return t.Next }
func after(t *egbug.T) *egbug.T  { return t.E2.Next }

eg output:

package egbug

type T struct {
    *E
    E2  *E
}

type E struct {
    Next *T
}

func main() {
    var t *T
    t.E2.E2.Next = new(T)
}

The second statement in main should be t.E2.Next, not t.E2.E2.Next. The output does not compile.
@josharian
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This is not just theoretical. I encountered it while working on a follow-up to CL 7360. Note that because the output doesn't typecheck, I can't just use eg to fix it as a workaround.

@josharian
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...and actually, it looks like this has to do with applying the transformation too many times, not with embedded fields. Sorry. Still a bug, though. :)

@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@rsc rsc changed the title cmd/eg: embedded fields are mishandled x/tools/cmd/eg: embedded fields are mishandled Apr 14, 2015
@rsc rsc modified the milestones: Unreleased, Unplanned Apr 14, 2015
@rsc rsc removed the repo-tools label Apr 14, 2015
@josharian josharian mentioned this issue May 22, 2015
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@Ripounet
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I noticed the same problem each time the "after" matches the "before" pattern, e.g. :

func before(str string) string { return strings.ToLower(str) }
func after(str string) string  { return strings.ToLower("[" + str + "]") }

-> brackets added twice instead of once.

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@josharian @mikioh @rsc @Ripounet @alandonovan