This git commit modifies the go compiler to support emitting warnings instead of errors when it encounters unused labels, variables, and imports. Warnings do not stop compilation or production of the final binary.

All changes to the upstream go compiler are contained within this one commit. From time to time, I'll rebase this commit onto upstream master and force-push to https://github.com/kstenerud/go master in order to keep it clean and current. To update to the latest version of this repo, you must first git fetch, git fetch --tags, and then git reset --hard origin/master. Warning: this will destroy all your local changes!

• Use Case
• Usage
• When will this go into mainline?
• Getting and Building the Modified Go Compiler
• Applying this Patch to a Specific Go Release
• Rebasing to upstream
• Helper Script
• Original Document

The use case for warnings is the exploratory development or debugging phases, where you really don't care about leaving unused things lying around for the time being (for example, temporarily commenting something out), and would rather that the compiler just got out of your way until you've got something ready to compile normally and commit.

go build -gcflags=-warnunused somefile.go
go test -gcflags=-warnunused

When you're done with your exploratory/debugging phase, simply build or test without the flag:

go build somefile.go
go test

Compiling without the flags will fail on unused things as normal.

example.go:

package main

import "fmt"

func main() {
    var start int = 1

    breakOuter:
    // for x := start; x < 10; x++ {
    for x := 3; x < 10; x++ {
        for y := 0; y < 10; y++ {
            result := y * 10 + x
            // fmt.Printf("Result: %d\n", result)
            // if result == 42 {
            //  fmt.Printf("Breaking")
            //  break breakOuter
            // }
        }
    }
}

Result of go build -gcflags=-warnunused example.go:

./example.go:8:2: Warning: label breakOuter defined and not used
./example.go:3:8: Warning: imported and not used: "fmt"
./example.go:6:6: Warning: start declared and not used
./example.go:12:4: Warning: result declared and not used

This feature will not be put into mainline golang: https://golang.org/doc/faq#unused_variables_and_imports

Download the source code, install a bootstrap compiler, and build!

• Go to https://github.com/kstenerud/go/releases
• Select the latest goX.Y.Z-warn tag

• git tag to get a list of tags
• git checkout goX.Y.Z-warn

The go tree must reside at /usr/local/go (according to https://golang.org/doc/install#install)

So for example: sudo tar -C /usr/local -xzf go1.12.6-warn.tgz

You can bootstrap from one of the official distributions at https://golang.org/dl

It must reside at $HOME/go1.4

For example:

wget https://dl.google.com/go/go1.12.7.linux-amd64.tar.gz
tar xf go1.12.7.linux-amd64.tar.gz
mv go $HOME/go1.4

mkdir -p /usr/local/go/bin
cp $HOME/go1.4/bin/go /usr/local/go/bin/

cd /usr/local/go/src
./make.bash

This will build the go compiler binaries and put them in /usr/local/go

To apply this change to a specific go release, simply checkout the tag, make a branch, cherry-pick this commit, and build.

Get the tag to cherry-pick:

$ git checkout master
$ git log --oneline -n 1
0e367a3c38 (HEAD -> master, origin/master, origin/HEAD) Support emitting warnings ...

Make a branch from your chosen tag and cherry-pick:

git checkout go1.12.6
git checkout -b go1.12.6-warn-branch
git cherry-pick 0e367a3c38

Build the compiler and run tests:

cd src
./all.bash

Make a new tag for your modified go compiler:

git tag -a go1.12.6-warn

To get the latest goodies from upstream and retain this patch:

git pull --rebase https://github.com/golang/go.git master
git fetch --tags https://github.com/golang/go.git

Here's a quick script to put this change into a specific go release. If using the commit from from master (the default) causes conflicts, try using one from a previous warn tag instead. For example:

make-go-patched-branch -s go1.13.3-warn go1.13.4

make-go-patched-branch:

#!/bin/bash

set -eu

if [[ ! $(git config --get remote.origin.url) =~ .*/go\.git$ ]]; then
    echo "This command must be run from inside the golang git repository"
    exit 1
fi

GO_RELEASE_SOURCE_TAG=master

show_help() {
    echo "Usage: $0 [options] <go release tag>"
    echo "Use git tag to get a list"
    echo
    echo "Options:"
    echo " -s <tag>: Use the commit from the specified warn tag instead of $GO_RELEASE_SOURCE_TAG (example: go1.13.4-warn)"
}

while getopts "s:" o; do
    case "$o" in
        s)
            GO_RELEASE_SOURCE_TAG=$OPTARG
            ;;
        *)
            show_help
            exit 1
            ;;
    esac
done
shift $((OPTIND-1))


if [[ $# -ne 1 ]]; then
    show_help
    exit 1
fi

GO_RELEASE_ORIGINAL_TAG=$1
GO_RELEASE_NEW_TAG=${GO_RELEASE_ORIGINAL_TAG}-warn
GO_RELEASE_BRANCH=${GO_RELEASE_NEW_TAG}-branch

git checkout $GO_RELEASE_SOURCE_TAG
WARNINGS_COMMIT=$(git rev-parse HEAD)

git checkout "$GO_RELEASE_ORIGINAL_TAG"
git checkout -b "$GO_RELEASE_BRANCH"
git cherry-pick $WARNINGS_COMMIT

echo "
New branch $GO_RELEASE_BRANCH created with warnings commit cherry-picked ($(git rev-parse HEAD))

Now you can build it:
    cd src
    ./all.bash or ./make.bash

When you're happy, tag it:
    git tag -a $GO_RELEASE_NEW_TAG
"

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

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Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

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After downloading a binary release, visit https://golang.org/doc/install or load doc/install.html in your web browser for installation instructions.

If a binary distribution is not available for your combination of operating system and architecture, visit https://golang.org/doc/install/source or load doc/install-source.html in your web browser for source installation instructions.

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