cmd/vet: "possible malformed +build comment" check too strict

[eliasnaur]

What version of Go are you using (go version)?

$ go version
go version devel +ffd096db2b Wed Feb 13 05:35:45 2019 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

I have a go generate line that prepends a +build comment to a C file:

//go:generate sed -i "1s;^;// +build linux,!android\\n\\n;" wayland_xdg_shell.c

What did you expect to see?

No warning from go vet or go test.

What did you see instead?

Running go vet or go test on the package results in:

os/os_wayland.go:14:1: possible malformed +build comment

I admit this is a special case.

[katiehockman]

/cc @alandonovan

[alandonovan]

It may be a special case, but vet could certainly do better. The presence of both // and " to the left of //+build should be quite enough to make it clear that this is a not a +build comment.

[mvdan]

Would it not be easier to skip lines beginning with //go:? It's very likely that the user is writing some form of compiler or tool directive in that case.

[adonovan]

I was going to say it seems rather too specific, but in fact the only comments vet looks at are those above the package declaration, excluding the package doc comment itself, which leaves only true +build declarations, copyright messages, and //go declarations. So I guess that would be fine.

But it wouldn't be hard to exclude any comments of the form //.*// +build.

[FiloSottile]

I am hitting this with an autogenerated file that contains a line like

// Autogenerated: 'fiat-crypto/src/ExtractionOCaml/unsaturated_solinas' --lang Go --no-wide-int --cmovznz-by-mul --internal-static --public-function-case camelCase --public-type-case camelCase --private-function-case camelCase --private-type-case camelCase --no-prefix-fiat --package-name fiat --doc-text-before-function-name '' --doc-prepend-header 'Code generated by Fiat Cryptography. DO NOT EDIT.' --doc-prepend-header '+build amd64 arm64 mips64 mips64le ppc64 ppc64le riscv64 s390x wasm' --doc-newline-before-package-declaration p521 64 9 '2^521 - 1' carry_mul carry_square carry add sub to_bytes from_bytes selectznz

[mvdan]

I wonder if we could just remove this vet rule in the short term, given that the syntax is being superseded by //go:build.