reexec: test cmd.Cancel, bump minimum go version to go1.20

[thaJeztah]

• stacked on reexec: add "CommandContext" #193

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reexec: test cmd.Cancel, bump minimum go version to go1.20

This requires go1.20 or up; https://go-review.googlesource.com/23300

[kolyshkin]

LGTM

(I dream about the day we can drop Go 1.18 entirely, and just use supported versions)

[thaJeztah]

Yeah, it's a bit of extra hassle, then again for modules that don't need it, it reduces having to update those. Perhaps we should check the go.mod for version, and based on that skip the module in the matrix (so that we don't have to maintain a list).

[thaJeztah]

This seems to work; I'll open a follow-up for that one.

#!/usr/bin/env bash

set -eu

# Check if the module's declared Go version is <= current Go version
go_version="$(go env GOVERSION)"
go_version="${go_version#go}"

packages=""
for p in */; do
  [ -f "$p/go.mod" ] || continue
  if ! (cd "$p" && go list -m -f "{{if gt .GoVersion \"$go_version\"}}ko{{end}}" | grep -q ko); then
    packages+="${p%/} "
  fi
done

echo "PACKAGES=${packages}"