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x/tools/cmd/eg: matches should be limited to value expressions #14728

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mdempsky opened this issue Mar 9, 2016 · 2 comments
Open

x/tools/cmd/eg: matches should be limited to value expressions #14728

mdempsky opened this issue Mar 9, 2016 · 2 comments
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Tools This label describes issues relating to any tools in the x/tools repository.
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@mdempsky
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mdempsky commented Mar 9, 2016 

$ cat a.go
package a
func before(x *int) int { return *x }
func after(x *int) int { return 42 }

$ cat b.go
package b
func x(p **int) {}

$ eg -t a.go b.go
=== b.go (1 matches)
package b

func x(p 42)    {}

The problem appears to be that in the type expression **int, the subexpression *int has type *int, so eg is deciding that it's a candidate match for the original expression. However, *int is a type expression, so it doesn't make sense to replace it with a value expression like 42.

I think eg needs to make use of go/types.TypeAndValue's IsValue method.

/cc @alandonovan
@mdempsky mdempsky added this to the Unreleased milestone Mar 9, 2016
@mdempsky
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The problem is that eg uses go/types.(*Info).TypeOf (in (*Transformer).matchWildcard) to find the type of a candidate expression to match against, but TypeOf doesn't distinguish type vs value expressions.

Easiest fix seems to be to duplicate TypeOf into eg and augment it with the extra type vs value logic. I'm curious if this functionality is useful to other go/types consumers though.

@gopherbot
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CL https://golang.org/cl/40772 mentions this issue.

@gopherbot gopherbot added the Tools This label describes issues relating to any tools in the x/tools repository. label Sep 12, 2019
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