x/tools/go/packages: NeedSyntax without NeedFiles/NeedCompiledGoFiles produces empty slice

[mdempsky]

The program below prints:

runtime (LoadMode(NeedName|NeedSyntax)):
	len(Syntax) = 0
	Errors: []

runtime (LoadMode(NeedName|NeedFiles|NeedSyntax)):
	len(Syntax) = 136
	Errors: []

runtime (LoadMode(NeedName|NeedCompiledGoFiles|NeedSyntax)):
	len(Syntax) = 145
	Errors: [/home/mdempsky/wd/go/src/runtime/asm.s:5:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/asm_amd64.s:5:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/duff_amd64.s:5:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/memclr_amd64.s:7:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/memmove_amd64.s:28:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/preempt_amd64.s:3:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/rt0_linux_amd64.s:5:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/sys_linux_amd64.s:9:1: illegal character U+0023 '#' /home/mdempsky/wd/go/src/runtime/time_linux_amd64.s:7:1: illegal character U+0023 '#']

I think only the middle case is working as documented.

The last case appears to be due to #56632.

package main

import (
	"fmt"
	"log"

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

func main() {
	var modes = []packages.LoadMode{
		packages.NeedName | packages.NeedSyntax,
		packages.NeedName | packages.NeedFiles | packages.NeedSyntax,
		packages.NeedName | packages.NeedCompiledGoFiles | packages.NeedSyntax,
	}

	for _, mode := range modes {
		cfg := packages.Config{Mode: mode}
		pkgs, err := packages.Load(&cfg, "runtime")
		if err != nil {
			log.Fatal(err)
		}
		pkg := pkgs[0]
		fmt.Printf("%v (%v):\n\tlen(Syntax) = %v\n\tErrors: %v\n\n", pkg.PkgPath, mode, len(pkg.Syntax), pkg.Errors)
	}
}

[gopherbot]

Change https://go.dev/cl/588141 mentions this issue: go/packages: document fields that are part of JSON schema