cmd/go: reject to download toolchain when gotoolchain < go directive

[xieyuschen]

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

$ go version
go version go1.24.0 darwin/arm64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/yuchen.xie/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/yuchen.xie/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/28/7sypdf0519xfl4ylhq_90s0m0000gp/T/go-build2459204566=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/Users/yuchen.xie/go/pkg/mod'
GONOPROXY='git.garena.com'
GONOSUMDB='git.garena.com'
GOOS='darwin'
GOPATH='/Users/yuchen.xie/go'
GOPRIVATE='git.garena.com'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/yuchen.xie/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.0'
GOWORK=''
PKG_CONFIG='pkg-config'
uname -v: Darwin Kernel Version 23.4.0: Fri Mar 15 00:10:42 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6000
ProductName:		macOS
ProductVersion:		14.4.1
BuildVersion:		23E224
lldb --version: lldb-1500.0.404.7
Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)

What did you do?

• Case1:

mkdir verify && cd verify
go mod init m
go mod edit -go=1.26 -toolchain=go1.23.0
go version

• Case2:

mkdir verify && cd verify
go mod init m
go mod edit -go=1.24 -toolchain=go1.23.0
<my-local-path>/bin/sdk/go1.21.10/bin/go version

What did you expect to see?

Both case 1 and case 2 should be rejected, because go.mod reference said.

The suggested Go toolchain’s version cannot be less than the required Go version declared in the go directive.

Hence, before we actually downloading toolchain, we should check the version inside go.mod and report an error.
For example, go: suggested go toolchain go1.23.0 cannot be less than required go version 1.24

Besides, the case2 looks weird in real usage.

What did you see instead?

• case1:

go: downloading go1.26.0 (darwin/arm64)
go: download go1.26.0 for darwin/arm64: toolchain not available

• case 2:

go: downloading go1.24 (darwin/amd64)
go: download go1.24 for darwin/amd64: toolchain not available

[gopherbot]

Change https://go.dev/cl/653237 mentions this issue: cmd/go: validate go and toolchain versions before downloading

[gabyhelp]

Related Issues

• cmd/go: go1.22 toolchain not available #65631 (closed)
• cmd/go get doesn't validate module arguments #71437 (closed)
• cmd/go: toolchain=auto doesn't upgrade version with local replacement module #71678 (closed)
• cmd/go: download go1.22 for darwin/arm64: toolchain not available #65568 (closed)
• Should the `go` directive in `go.mod` a semver version (including patch), or not? #68971 (closed)
• cmd/go: go toolchain version switch doesn't work when only language version is set in go.mod #65580 (closed)
• cmd/go: can't invoke go in src directory #67853 (closed)
• go mod edit: changing go versions in modules to invalid versions updates go.mod and causes weird problems #66491 (closed)
• cmd/go: mod tidy reports toolchain not available with 'go 1.21' #62278 (closed)
• golang.org/x/*: go directive of 1.23.0 is forcing toolchain directives in anything not using exactly go1.23.0 #71864 (closed)

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