x/tools/go/packages: log.Fatalf inside library routine

[rsc]

This program triggers a log.Fatalf inside golang.org/x/tools/go/packages.

% ls
go.mod	go.sum	x.go
% cat go.mod
module m

go 1.16

require golang.org/x/tools v0.1.0 // indirect
% cat x.go
package main

import "golang.org/x/tools/go/packages"

func main() {
	cfg := &packages.Config{
		Mode: packages.NeedName | packages.NeedTypes | packages.NeedExportsFile,
	}
	packages.Load(cfg, "fmt")
}
% go run .
2021/04/15 10:31:34 Unexpected package creation during export data loading
exit status 1
%

[rsc]

I added some debug prints and am pretty confused.

2021/04/15 11:58:51 Unexpected package creation during export data loading fmt 1 7:
old map[]
new map[fmt:package fmt ("fmt") internal/poll:package poll ("internal/poll") io:package io ("io") io/fs:package fs ("io/fs") os:package os ("os") syscall:package syscall ("syscall") time:package time ("time")]

This all looks fine. Reading the fmt export data will build stub packages for a bunch of its dependencies.

[rsc]

I found it. impliedLoadMode should set NeedImports for NeedExportFile. Will send CL.

[gopherbot]

Change https://golang.org/cl/310512 mentions this issue: go/packages: fix load with NeedTypes but not NeedImports

[AlekSi]

@rsc @matloob @aclements ping. Should it still be merged?

[bradfitz]

@rsc, what's the status here? Were you going to merge your changes?