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go/doc: panic in go/doc.lastComment when parsing an Example_foo with no body #29271

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bcmills opened this issue Dec 14, 2018 · 6 comments
Closed

go/doc: panic in go/doc.lastComment when parsing an Example_foo with no body #29271

bcmills opened this issue Dec 14, 2018 · 6 comments
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FrozenDueToAge help wanted NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Go1.13

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@bcmills
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bcmills commented Dec 14, 2018

@alandonovan found this panic in #28044: https://play.golang.org/p/Gs4iMjqFmgu

With this input program:

package p
func Example() {}
func Example_a()

doc.Examples panics with this stack trace:

go/ast.(*BlockStmt).Pos(...)
	/usr/local/go/src/go/ast/ast.go:728
go/doc.lastComment(0x0, 0x0, 0x0, 0x0, 0x15d060, 0x92a)
	/usr/local/go/src/go/doc/example.go:409 +0x6
go/doc.exampleOutput(0x0, 0x0, 0x0, 0x0, 0x1, 0x0, 0x40e238, 0x0)
	/usr/local/go/src/go/doc/example.go:108 +0x40
go/doc.Examples(0x42bf90, 0x1, 0x1, 0x197480, 0x1e9cb8, 0x0, 0x437580, 0x0)
	/usr/local/go/src/go/doc/example.go:75 +0x320

CC @griesemer
@bcmills bcmills added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Dec 14, 2018
@bcmills bcmills added this to the Go1.13 milestone Dec 14, 2018
@griesemer griesemer self-assigned this Dec 14, 2018
@griesemer
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Probably missing a nil check somewhere when there' no function body (*ast.BlockStmt is nil).

@rcodeb
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rcodeb commented Dec 15, 2018

Sorry to barge in, I believe, https://github.com/golang/go/blob/master/src/go/doc/example.go#L389 here there should be a check for the nil body.

@agnivade
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Will take a look.

@agnivade agnivade assigned agnivade and unassigned griesemer Dec 16, 2018
@gopherbot
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Change https://golang.org/cl/154380 mentions this issue: go/doc: handle Examples with no body

@rcodeb
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rcodeb commented Dec 16, 2018

@agnivade may be return from the function where I pointed in my comment as returning nil will be ok for pointer to file return type.

@agnivade
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Please comment on the CL as it will be easier to review there.

@golang golang locked and limited conversation to collaborators Dec 16, 2019
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@agnivade @dmitshur @bcmills @griesemer @gopherbot @rcodeb