Error building docker container due to local package import in main.go file

I am trying to build a Docker container for my Go project, but I keep encountering the following error:

=> ERROR [backend-builder 5/5] RUN --mount=type=cache,mode=0777,target=/go/pkg/mod \
--mount=type=cache,mode=0777,target=/.cache/go-build \
CGO_ENABLED=0 GOOS=linux go build -o serve ./backend/cmd/main.go: \
#17 0.343 backend/cmd/main.go:10:2: no required module provides package \
github.com/LarsDepuydt/peno-entrepreneurship-3d-oclusion/backend/cmd/serve; \
to add it: \
#17 0.343 go get github.com/LarsDepuydt/peno-entrepreneurship-3d-oclusion/backend/cmd/serve \
------
executor failed running [/bin/sh -c CGO_ENABLED=0 GOOS=linux go build -o serve ./backend/cmd/main.go]: exit code: 1

I suspect that the error is caused by the fact that my main.go file imports a local package called serve from my project.

This is my project structure:

peno-entrepreneurship-3d-oclusion/
│
├── backend/
│   ├── cmd/
│   │   ├── main.go
│   │   └── serve/
│   │       └── serve.go
│   ├── go.mod
│   └── go.sum
│
├── Dockerfile
│
└── ... (other frontend files and directories)

This is my import statement in my main.go:

import (
	"database/sql"
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/LarsDepuydt/peno-entrepreneurship-3d-oclusion/backend/cmd/serve"
)

This is my docker file:

################################
# Build backend
################################

FROM dev AS backend-builder

# Change the WORKDIR in the backend-builder stage
WORKDIR /usr/src/app

# pre-copy/cache go.mod for pre-downloading dependencies and only redownloading them in subsequent builds if they change
COPY ./backend/go.mod ./backend/go.sum ./
RUN --mount=type=cache,mode=0777,target=/go/pkg/mod go mod download
#RUN go get github.com/LarsDepuydt/peno-entrepreneurship-3d-oclusion/backend/cmd/serve

COPY . .

# Use native go packages (CGO_ENABLED)
RUN --mount=type=cache,mode=0777,target=/go/pkg/mod \
    --mount=type=cache,mode=0777,target=/.cache/go-build \
    CGO_ENABLED=0 GOOS=linux go build -o serve ./backend/cmd/main.go

Could someone please help me explain what goes wrong here? I have tried a lot of things with changing the path but can't get around this error.

In main.go I tried this: "./serve" instead of the current import.

I also tried many things regarding the WORKDIR and the path in the docker file. But I keep getting the same error and can't seem to fix the error.

On the Dockerfile, you use the following scripts:

WORKDIR /usr/src/app
COPY ./backend/go.mod ./backend/go.sum ./
RUN --mount=type=cache,mode=0777,target=/go/pkg/mod go mod download

With that, the go.mod file is located right under /usr/src/app, and the same path will become the root path of your go module.

Based on your code structure, the go.mod should be located under /usr/src/app/backend, NOT in /usr/src/app.

Try to change the script to this one below:

FROM dev AS backend-builder

WORKDIR /usr/src/app/backend
COPY ./backend/go.mod ./backend/go.sum ./
RUN --mount=type=cache,mode=0777,target=/go/pkg/mod go mod download

WORKDIR /usr/src/app
COPY . .

WORKDIR /usr/src/app/backend
RUN --mount=type=cache,mode=0777,target=/go/pkg/mod \
    --mount=type=cache,mode=0777,target=/.cache/go-build \
    CGO_ENABLED=0 GOOS=linux go build -o serve ./cmd/main.go