I got a Go API up on Heroku to which I push some code; in my procfile I have the following
web: main
In order to launch the Go built binary on Heroku's side. When I build it on my side with
go build cmd/main.go
It produces a binary file namned 'main' in my project root and works as expected but on Heroku I get
app[web.1]: bash: main: No such file or directory
The build process on Heroku seems fine, it finds all my dependencies and installs/compiles it all.
This was super simple once I realised this;
All main packages in the repo are compiled and binaries placed in the /app/bin directory, which is in the PATH. Binaries are named after the directory that contains them.
Another thing to note: Like other Go programs, the code in main.go has to belong to package main:
package main
func main() {
// your code here
}
I'm afraid I totally forgot about this at first and it stumped me for a while.
Related
I build a simple "Hello, World" wasm app like:
GOARCH=wasm GOOS=js go build -o lib.wasm main.go
All is well. But then I want to test my code in my local (Linux) environment. So I change it to a pretty standard:
package main
import "fmt"
func main () {
fmt.Println("test")
}
And do a simple:
go run .
but now I get:
package xxx: build constraints exclude all Go files in xxx
I understand that if I specify a wasm build, I can't expect to run it locally. But I'm not trying to do a wasm build anymore. There are no build constraints in my .go source file, and my go.mod file just has the package and go version.
If I copy these file to a new directory and only do the go run . without the wasm build - all is good.
And if I do:
go build filename.go
it works properly.
It's like something "remembers" that this directory was supposed to be built with wasm - but I cant find what/where.
Is there a cache or something elsewhere that's remembering some build settings that I need to clear? I've tried go clean and go clean -cache - no luck!
The answer seems to be that if a filename ends in wasm.go - go will assume this is indeed a wasm file.
This means that a normal build or run will fail (if you don't specify proper OS and arch) - though a run with an explicit filename (even if it ends in wasm.go will work correctly.
???
PROBLEM: functions exported from other packages are undefined, invisible from inside of main.go
SOLUTION:
Put main.go into a separate folder (name it app or main, doesn't matter). Only go.mod remains in root, with the folders "app" and "package1" "package2" etc. After this VSCode automatically added imports on save, I didn't even need to do anything. If I have main.go in root then it doesn't work (most of the time) as it doesn't "see" functions from other modules (undefined).
I found the solution HERE,(see post by davidbost). The solution on this page by Andrey Dyatlov worked too for a while and then stopped working.
It took me probably 10 hours of try and error and searching.
Hopefully the above will help others. Thank you, everyone!
_______________________________________________________________________
Original Problem Description:
Windows 10, Go 1.17, VS Code with Go extension.
Hello, I am new to Go and I was not able to follow a single tutorial due to the following issue. When I create another .go file in the same directory (or inside a folder of the same directory) as the main.go, I receive error saying .\main.go:7:2: undefined: SayHi
main.go file:
package main
import "fmt"
func main() {
fmt.Println("1st")
SayHi()
}
another .go file inside /something folder:
package something
import "fmt"
func SayHi() {
fmt.Println("Hi!")
}
Running go run main.go results in the undefined SayHi error
I googled the issue with no luck.
$ go build // gives out the same error
$ go install // gives out the same error
without using functions from other files $ go run main.go runs just fine.
I also tried go init with adding my github directory with no luck (by following a tutorial). I also tried the official starting guide with go run init, and the exported Capitalized function is still undefined. What's worse is that autocomplete for the SayHi function works, yet it won't compile because undefined.
I have set PATH to C:\Users\xxx\go and put my files there, I also tried using C:\Go with no luck, it's still undefined. I'm about to give up on Go...
It' would be hard to fix your project without knowing its current state. Please, try to start from scratch:
Create a directory for your project anywhere outside $GOPATH:
mkdir myproject
cd myproject
Run the following command to create a go.mode file that describes your project (module) and its dependencies; let's call the module github.com/me/myproject:
go mod init github.com/me/myproject
Create the first file; let's call it main.go:
package main
import "fmt"
import "github.com/me/myproject/something"
func main() {
fmt.Println("1st")
something.SayHi()
}
Create a directory for the package called github.com/me/myproject/something:
mkdir something
Create a file with path something/something.go:
package something
import "fmt"
func SayHi() {
fmt.Println("Hi!")
}
From the myproject directory, run go build.
Launch your first Go program:
./myproject
1st
Hi!
I am confused about how to layout my Go project and then how to build it. I am reasonably new to Go and believe there was a time <1.13 where the GOPATH was important. I am using 1.14, so I believe I do not have to care about that and GOPATH is not set. I do not (for the moment) host my code on GitHub (which is something various articles assume). I have read a number of things, but it all leaves me more confused:
https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies
https://www.wolfe.id.au/2020/03/10/starting-a-go-project/
https://talks.golang.org/2014/organizeio.slide#1
I have laid out my project according to this: https://github.com/golang-standards/project-layout. (Except this project seems to use a Makefile. I do not want to write a Makefile. I believe this should all work without a Makefile. I really do not want to write a Makefile.)
Here is the structure:
/src
/cmd
main.go
/internal
helper.go
go.mod
go.mod looks like this:
module mycompany/mymodule
go 1.14
service.go looks as follows
package main // this has to be called 'main'
import (
"mycompany/mymodule/internal/helper"
)
func main () {
helper.greet("Jenny")
}
So, if I am in /src and I run build cmd/service.go I get
cmd/service.go:4:2: package mycompany/mymodule/internal/helper is not in GOROOT (/usr/local/Cellar/go/1.14.5/libexec/src/mycompany/mymodule/internal/helper)
Do I have to compile helper.go first? Manually? Surely not. go build surely should be able to build my entire project, right? Including all the dependencies. Could someone please tell me what I am missing?
When you run go build without specifying file path, it will look for the main function inside any .go files at current directory to start. It doesn't build entire project. But it wouldn't be a problem in this case.
You're importing wrong package. The package name to import must be mycompany/mymodule/internal not mycompany/mymodule/internal/helper.
And to invoke a function inside another package, it must be exposed to outside.
So you have to declare the function greet() as Greet()
I'm trying to write a basic go program that calls a function on a different file, but a part of the same package. However, it returns:
undefined: NewEmployee
Here is the source code:
main.go:
package main
func main() {
emp := NewEmployee()
}
employee.go:
package main
type Employee struct {
name string
age int
}
func NewEmployee() *Employee {
p := &Employee{}
return p
}
func PrintEmployee (p *Employee) {
return "Hello world!"
}
Please read "How to Write Go Code".
Use go build or go install within the package directory, or supply an import path for the package. Do not use file arguments for build or install.
While you can use file arguments for go run, you should build a package instead, usually with go run ., though you should almost always use go install, or go build.
I just had the same problem in GoLand (which is Intellij IDEA for Go) and worked out a solution. You need to change the Run kind from File to Package or Directory. You can choose this from a drop-down if you go into Run/Edit Configurations.
Eg: for package ~/go/src/a_package, use a Package path of a_package and a Directory of ~/go/src/a_package and Run kind of Package or Directory.
If you're using go run, do go run *.go. It will automatically find all go files in the current working directory, compile and then run your main function.
You can try one of the following:
Method 1:
Assume that your project name is MyProject
Go to your path, run go build
It will create an executable file as your project name ("MyProject")
Then run the executable using ./MyProject
You can do both steps at once by typing go build && ./MyProject. Go files of the package main are compiled to an executable.
Method 2:
Just run go run *.go. It won't create any executable but it runs.
go run . will run all of your files. The entry point is the function main() which has to be unique to the main package.
Another option is to build the binary with go build and run it.
If you want to call a function from another go file and you are using Goland, then find the option 'Edit configuration' from the Run menu and change the run kind from File to Directory. It clears all the errors and allows you to call functions from other go files.
you should use go modules now, if you are not following How to write go code
With go module you don't have to put the code in the $GOPATH/src. it can live in any other location as well.
You can move the code to different directory like /employee, To make it work Just under employee directory initialise the go module
go mod init example.com/employee
I ran into the same issue with Go11, just wanted to share how I did solve it for helping others just in case they run into the same issue.
I had my Go project outside $GOPATH, so I had to turned on GO111MODULE=on without this option turned on, it will give you this issue; even if you you try to build or test the whole package or directory it won't be solved without GO111MODULE=on
While this doesn't directly address the OP's specific issue, I thought I'd chime in with the solution to my "undefined" error: the file with the undefined method had a build constraint (build tag).
More specifically, I accidentally included a build constraint to remove testing files from my deployed application binary in a utility function file used by my deployed binary. So in the OP's example - if employee.go had a build constraints their go build command would need to include a -tags flag matching the constraint in in order to have the file included.
For more info read this blog post:
https://dave.cheney.net/tag/build-constraints
Took a while to drill down my own MRE for this, so hopefully it will help others, despite being brief:
This can also occur if your functions / structs are defined in a file that has import "C", which will be silently ignored if CGO_ENABLED=0 is in your go environment, leading to you staring at a two file package that somehow is unable to share between themselves.
In GoLand,
right click a directory
GoLand will give you the option for build it and run it
it will also create a run configuration draft for you
you can save with an option of the upper right dropdown
If you right clic a file, it shows you commands to run, debug, test that file.
If you right clic a directory, it will be the same for that "package", expecting a main.go file inside the directory
I had a nasty import "C" in one of my go files.
If your source folder is structured /go/src/blog (assuming the name of your source folder is blog).
cd /go/src/blog ... (cd inside the folder that has your package)
go install
blog
That should run all of your files at the same time, instead of you having to list the files manually or "bashing" a method on the command line.
Off topic but still :-)
Before:
func NewEmployee() *Employee {
p := &Employee{}
return p
}
After:
func NewEmployee() *Employee {
return &Employee{}
}
No need to create a new variable. Just return.
I'm playing with Google Go and I'm having fun (!), but I'm having some problems with package subsystem.
I'm running Go 1.0.1 on Mac OS X Lion. I've build also various single file programs without problems (I've also build a small webapp using html/templates without problems and it compiles and runs without any error).
I've defined a "reusable" package (even.go):
package even
func Even(i int) bool {
return i % 2 == 0
}
func Odd(i int) bool {
return i % 2 == 1
}
and a consumer program (useeven.go):
package main
import (
"./even"
"fmt"
)
func main() {
a := 5
b := 6
fmt.Printf("%d is even %v?\n", a, even.Even(a))
fmt.Printf("%d is odd %v?\n", b, even.Odd(b))
}
But when I compile the "library" using
go build even.go
I got nothing... No errors, no message... What happens?
How should I do this?
The answer to your question, "How should I do this?" is explained in How to Write Go Code. It's really pretty important stuff and worth taking a look at.
The behavior of go build might seem puzzling, but is actually conventional for command line programs--no output means that the program ran successfully. So what did it do? For that your answer is in go help build
... Otherwise build compiles the packages but discards the results,
serving only as a check that the packages can be built.
What, you wanted more? Of course. "How to Write Go Code" explains good ways of doing this. For a quick fix to your program, I'll explain that the go command expects each package and each executable program to be in a separate directory. If you just make a directory called even, immediately under the location of useeven.go, and move even.go to it, then go run useeven.go should run just as you have it.
go build only generates an output file when it builds a "single main package". If you want to output a file for your other package you should use go install. That will build and install that package to your pkgs directory.
As noted in a comment by the OP, go build and go run useeven.go work fine, once you put even.go in its own folder: ./even/even.go. There is a bit of Go magic in the ./ (in the import) that makes the "local package" build automatically without requiring it to be installed anywhere.
useeven/
├── even
│ └── even.go
└── useeven.go
If you wanted to make this work without the magic ./, then the library need to be installed. A quick-and-dirty way (at the risk of polluting your library namespace) of making this work for your project is to simply register the library's source location by using a symbolic link like so (in this example GOPATH is ~/go):
[ useeven ]
$ ln -s $(pwd)/even ~/go/src
Now when you build the program, it automatically performs a go get even to install an up-to-date version of your library.
Note that this doesn't make go install* work for the library, it just makes doing that unnecessary.
There are more idiomatic ways of doing this, if you're not in a hurry: How to import local packages in go?
The reason that output is not being generated here is because you're running the
go build even.go
command on the package and not the main go file. Doing so on the package will check for errors on the package, but because it's not a main with an output, no success messages will be generated. If there are issues with the package's contents, errors will be displayed, otherwise if it compiles fine there will be no output
Instead, you should run:
go build useeven.go
To create the binary, then to execute the binary and get output from the program:
./useeven