Considering the sample hello world with the wrong package name with the file named as main.go
package test
import "fmt"
func main() {
fmt.Println("hello world")
}
on go build main.go the build doesn't work (doesn't generate the executable) because of the incorrect package name. But why no error is thrown?
A package name test is not incorrect, it is valid according to Spec: Package clause:
PackageClause = "package" PackageName .
PackageName = identifier .
test is a valid Go identifier.
As to what does go build main.go do?
Generally you list packages to go build, but you may also list .go source files, just as in your example.
Quoting from go help build:
If the arguments to build are a list of .go files, build treats them as a list of source files specifying a single package.
So go build simply built your test package, consisting of a single main.go source file. It is not an error to add a main() function to a package that is not main.
As to why "nothing" happens: go build generates no output if everything is ok, and it outputs error if something is not right. go build applied on a non-main package just "checks" if the package can be built, but it discards the result. Please check What does go build build?
Related
I am writing units test. I put all of the test files in other directory. Let's say the folder mypack.
There two files in the folder fun1_test.go and base.go.
The base.go has same common basic functions which are called by fun1_test.go. The base.go looks like:
package mypack_test
import (
.....
)
func Base1() {
// some code
}
The func1_test.go has functions which test func1. The func1_test.go looks like:
package mypack_test
import (
.....
)
func TestFunc1() {
// some code
Base1()
// some code
}
When I use command
go test func1_test.go base.go
There will be an error:
can't load package: package main: found packages mypack (func1_test.go) and mypack_test (base.go)
Can any one tell me why this happend. I know If the change the file base.go to base_test.go. The command will work ok. But I want to know why.
UPDATE:
I notice some of you guys misunderstanding the problem. The problem is not about if the two file need the other packages or one can call one.
The problem is that: If you have two file with same package, the package name looks like xxx_test. But the two files' name are yyy_test.go and zzz.go. When using go test yyy_test.go zzz.go command, there will be an error said they two file not in same packages.
The error are: can't load package: package main: found packages xxx (yyy_test.go) and xxx_test (zzz.go)
You should follow go's best practices.
That is:
Package names should contain only letters with no underscores.
Test file should be name of original file + test like: base.go - base_test.go.
Run test by going to packages directory and running go test.
If you make those changes, your tests should run without any problems.
If you checkout the go help test command there is this:
Test files that declare a package with the suffix "_test" will be
compiled as a separate package, and then linked and run with the main
test binary.
What is happening is that your file yyy_test.go is recognised as a test file because of its _test.go ending. The package defined in that file package xxx_test is considered to be the test version of the xxx package.
See this stack answer for desc: https://stackoverflow.com/a/31443271/6376471
Then, along comes zzz.go which is not recognised as a test file, because it's missing the _test.go suffix, it has a packge xxx_test which is not considered to be a test package.
This means that essentially you are defining the packages xxx_test from zzz.go and xxx from yyy_test.go, even though yyy_test.go actually defines xxx_test, but it's in a test file so handled differently.
Solutions:
Identify zzz.go as a test file by making it zzz_test.go.
Set zzz.go to have the non test package name package xxx instead of package xxx_test.
When I run this command
go test -tags integration $(go list ./... | grep -v /vendor/)
go fails with this for some packages that has all tests marked with // +build !integration
can't load package: build constraints exclude all Go files
Is there a way I can make go test ignore those packages in this case, instead of failing? Thanks
You will only get that error if all the files in the package are excluded by your build constraints, not just the test files. If that's what you want, just add a single package file with no code and the package will still be able to be loaded. For example, many packages put their package level docs in a separate file, which you could use to always have a valid package:
// Package foo does foo
package foo
For whatever it's worth : I was seeing similar errors while building my code. In my case, my main file had // +build go1.13 at the top of it and I was trying to get the file built using go1.12.x. Removing +build go1.13 fixed the issue.
The package you are importing might contain some source files with a conditional complication flag, which is a directive you may find at the top of the files like:
//+build linux darwin windows
package main
import "fmt"
func main() {
fmt.Println("hello")
}
The +build directive followed by one or multiple platforms indicates where this source code is supposed to be compiled on.
Therefore, you can simply try removing this directive to resolve the failure.
It worked for me.
Following on from snowfox's answer, if you can't remove the directive (becuase it was likely put there for a reason), you can still run the test by using the tag that was applied to that file (more info here).
If your file start looks like this:
//go:build bar
package foo
Then you can run the test by running go test ./foo_test.go --tags=bar
I have a small go demo project in Gogland with the structure:
awsomeProject
->src
->awsomeProject
->configuration.go
->main.go
Configuration file has a simple structure just for demo:
configuration.go:
package main
type Config struct {
Data int
}
Main file just uses the Config struct:
main.go
package main
import "fmt"
func main(){
var cfg Config
cfg.Data = 1
fmt.Println("lalala")
}
The error that I have is:
/usr/local/go/bin/go run /Users/lapetre/Work/awsomeProject/src/awsomeProject/main.go
command-line-arguments
src/awsomeProject/main.go:6: undefined: Config
Process finished with exit code 2
Any idea why the Config is not seen in main?
Thanks
When you build reusable pieces of code, you will develop a package as a shared library. But when you develop executable programs, you will use the package “main” for making the package as an executable program. The package “main” tells the Go compiler that the package should compile as an executable program instead of a shared library. The main function in the package “main” will be the entry point of our executable program.
That's why you should use the following structure:
awsomeProject
->src
->awsomeProject
->configuration.go
->main.go
with main.go
package main
import "fmt"
func main(){
var cfg awsomeProject.Config
cfg.Data = 1
fmt.Println("lalala")
}
and configuration.go
package awsomeProject
type Config struct {
Data int
}
For more details:
https://golang.org/doc/code.html
https://thenewstack.io/understanding-golang-packages
How are you calling go run? If you're calling it like
go run main.go
then that's the problem.
Go run only runs the file(s) you tell it to. So you need to tell it to also run configuration.go, or if you have several go files to run you can use
go run *.go
as eXMoor suggested.
There are some limits/drawbacks to "go run *.go" however, so the better alternative is to use go build instead of go run.
go build
Will compile everything. Then, to run the executable:
./awesomeProject
To combine all of this into one command that will compile and run whatever app you're working on, you can use:
go build && ./${PWD##*/}
I have it aliased to
gorunapp
just to make it easier.
This may not actually be the answer to the problem you're having, but hopefully you'll find it useful information regardless.
Try to run your application with command:
go run *.go
How to reference MyStruct in another file in the same package or folder?
Currently I get undefined: MyStruct when go build lib/file_2.go. I can run go install with no error, should I just ignore the build error?
These are my files:
lib/file_1.go
...
package lib
...
type MyStruct struct{
}
....
lib/file_2.go
...
package lib
...
{
m MyStruct
}
....
Thanks
This command works for me
go run *.go
Actually this will compile all go file and run your main function. So this works well
You're asking the go tool to compile lib/file_1.go, you never mention lib/file_2.go so how is it supposed to know it should compile it?
From go help build:
Build compiles the packages named by the import paths,
along with their dependencies, but it does not install the results.
If the arguments are a list of .go files, build treats them as a list
of source files specifying a single package.
You should be able to use MyStruct directly, since it is in the same package as its definition.
If you have any issue, sometimes it can help (for an IDE like SublimeText + GoSublime, for instance) to do a go install before creating lib/file_2.go.
That way, lib/file_1.go is compiled and present in GOPATH/pkg, with lib/file_1.go definitions visible for lib/file_2.go to use during its compilation.
According to https://golang.org/doc/tutorial/getting-started, you should run:
go run .
You have to compile the multiple files using the build command first.
go build
Now you can see a build file got generated with the given name or the folder name in case of default. Then run the binary.
./binary_file_name
I have a project that provides a library (exports some funcs) and also must provide a command-line interface (there must be an executable file).
Example of directory structure:
whatever.io/
myproject/
main.go
myproject.go
The go compiler needs the package main and func main to start execution. My library needs the package myproject where I put stuff on it. This is what the go tool says when I am building another project that tries to import myproject:
main.go:5:2: found packages myproject (myproject.go) and main (main.go) in $GOPATH/src/whatever.io/myproject
So I believe there is no way to do it.
Should I move the library or the CLI to another package?
Just move your packages inside a new folder within the same directory of main.go.
Remember to import the new package from the reference of the $GOPATH.
Example:
user#user:~/p/go/test/so-multipack$ ls -R
.:
a main.go
./a:
a.go
user#user:~/p/go/test/so-multipack$ cat main.go
package main
import (
"../so-multipack/a"
)
func main(){
a.Hello()
}
user#user:~/p/go/test/so-multipack$ cat a/a.go
package a
import (
"fmt"
)
func Hello(){
fmt.Println("hello from a")
}
user#user:~/p/go/test/so-multipack$ go run main.go
hello from a
user#user:~/p/go/test/so-multipack$ go build
user#user:~/p/go/test/so-multipack$ ls
a main.go so-multipack
user#user:~/p/go/test/so-multipack$
Useful link:
go build vs go build file.go
You cannot have two packages per directory, hence the error. So the solution as #Larry Battle said to move your myproject.go to a new directory.
From How to write go code
Go code must be kept inside a workspace. A workspace is a directory
hierarchy with three directories at its root:
src contains Go source files organized into packages (one package per directory),
pkg contains package objects, and
bin contains executable commands.
In most cases, no. However, there is an exception for unit tests.
Working Example:
Here are 2 different packages (mypackage and mypackage_test) in 1 directory (mypackage). The compiler will not complain about this.
mypackage folder:
mypackage/
foo.go
foo_test.go
mypackage/foo.go:
package mypackage
func Add(a int, b int) int {
return a + b
}
mypackage/foo_test.go:
package mypackage_test
// Unit tests...
Rules:
The 2 packages must have the following names:
NameOfDirectory.
NameOfDirectory + _test.
The names of the files in the _test package must end with _test.go
If you're receiving a confusing compiler error along the lines of found packages "foo" and "bar", you've probably broken one or more of these rules.
You can't have two golang files in one directory with two packages. So you need to move main.go out of myproject.
the directory structure before move
whatever.io/
go.mod
myproject/
main.go
myproject.go
After move
whatever.io/
go.mod
main.go
myproject/
myproject.go
And you need to change your main.go's import path. If the module name is aaa
Before
import "aaa"
Need change to this
import "aaa/myproject"