Unable to build go program in multistage build with undefined error in Docker

I am trying to learn go and I have build my first go program on something simple as.

❯ tree .
.
├── README.md
├── convert.go
├── dockerfile
├── go.mod
├── go.sum
├── main.go
├── pageindices.go
├── pageindices_test.go
├── pdf2png.go
└── pdf2png_test.go

what my docker file looks like the following

ARG GOLANG_IMAGE_TAG="1.20.6-alpine"
FROM golang:${GOLANG_IMAGE_TAG} as base

ARG PDF2IMG_VERSION=dev

# So using 8.14.2 for now
ARG VIPS_VERSION="8.14.2"

RUN apk update && apk add --no-cache \
     automake build-base pkgconfig glib-dev expat-dev gobject-introspection \
     libjpeg-turbo-dev libpng-dev libwebp-dev giflib-dev librsvg-dev libexif-dev lcms2-dev
# Exit 0 added because warnings tend to exit the build at a non-zero status
RUN cd /root \
    && mkdir vips \
    && wget -q0- "https://github.com/libvips/libvips/releases/download/v${VIPS_VERSION}/vips-${VIPS_VERSION}.tar.gz" | tar -xzf - -C vips --strip-components=1 \
    && cd vips \
    && CFLAGS="-g -O3" CXXFLAGS="-D_GLIBCXX_USE_CXX11_ABI=0 -g -O3" ./configure \
        --disable-debug \
        --disable-dependency-tracking \
        --disable-introspection \
        --disable-static \
        --enable-gtk-doc-html=no \
        --enable-gtk-doc=no \
        --enable-pyvips8=no && \
    make && make install-strip && ldconfig; exit 0
RUN export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/vips/lib
RUN apk del automake build-base

# create a working directory inside the image
WORKDIR /go/src/github.com/felixgao/pdf2img
# Cache go modules
ENV GO111MODULE=on

# Copy go mod and sum files
COPY go.mod go.sum ./

# Download all dependencies. Dependencies will be cached if the go.mod and go.sum files are not changed
RUN go mod download


# copy directry files i.e all files ending with .go 
COPY *.go .

# Build the Go app with ldflags
RUN CGO_ENABLED=0 GOOS=linux go build -a \
    -ldflags="-s -w -h -X main.Version=${PDF2IMG_VERSION}" \
    -o pdf2png


# build target image
FROM golang:${GOLANG_IMAGE_TAG} as prod
WORKDIR /app/
RUN apk --update add --no-cache \
    fftw glib expat libjpeg-turbo libpng \
	libwebp giflib librsvg libgsf libexif lcms2
WORKDIR /root/
COPY --from=base /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=base /root/libs/* /root/libs/
COPY --from=base /usr/local/lib/* /usr/local/lib/
COPY --from=base /go/src/github.com/felixgao/pdf2img/pdf2png .


#tell docker what port to expose
EXPOSE 8080

# Run the binary program produced by `go install`
CMD ["./pdf2png"]

my go.mod file looks like

module github.com/felixgao/pdf_to_png

go 1.20

require github.com/davidbyttow/govips/v2 v2.13.0

require (
	golang.org/x/image v0.9.0 // indirect
	golang.org/x/net v0.12.0 // indirect
	golang.org/x/text v0.11.0 // indirect
)

When I built it, it kept telling me the required package is not there. I thought go mod download would pull that down for me. Am I missing something?

=> CACHED [base  6/10] WORKDIR /go/src/github.com/felixgao/pdf2img                    0.0s
 => CACHED [base  7/10] COPY go.mod go.sum ./                                          0.0s
 => [base  8/10] RUN go mod download                                                   6.0s
 => [base  9/10] COPY *.go .                                                           0.0s
 => ERROR [base 10/10] RUN CGO_ENABLED=0 GOOS=linux go build -a     -ldflags="-s -w -  4.5s
------
 > [base 10/10] RUN CGO_ENABLED=0 GOOS=linux go build -a     -ldflags="-s -w -h -X main.Version=dev"     -o pdf2png:
#18 4.394 # github.com/felixgao/pdf_to_png
#18 4.394 ./pdf2png.go:29:29: undefined: vips.ImageType
#18 4.394 ./pdf2png.go:30:7: undefined: vips.ImageTypeJPEG
#18 4.394 ./pdf2png.go:31:7: undefined: vips.ImageTypePNG
#18 4.394 ./pdf2png.go:32:7: undefined: vips.ImageTypeTIFF
#18 4.394 ./pdf2png.go:35:41: undefined: vips.ImageType
#18 4.394 ./pdf2png.go:36:15: undefined: vips.ImageTypeJPEG
#18 4.394 ./pdf2png.go:37:15: undefined: vips.ImageTypePNG
#18 4.394 ./pdf2png.go:38:15: undefined: vips.ImageTypeTIFF
#18 4.394 ./pdf2png.go:41:25: undefined: vips.ImageRef
#18 4.394 ./pdf2png.go:41:86: undefined: vips.ImageMetadata
#18 4.394 ./pdf2png.go:41:86: too many errors
------
executor failed running [/bin/sh -c CGO_ENABLED=0 GOOS=linux go build -a     -ldflags="-s -w -h -X main.Version=${PDF2IMG_VERSION}"     -o pdf2png]: exit code: 1pdf2png]: exit code: 1

When run the build command locally, it works fine.

❯ go build -a -ldflags="-s -w -h -X main.Version=dev" -o pdf2png && echo $?
0
❯ ls -al pdf2png
-rwxr-xr-x  1 ggao  staff  6334226 Jul 18 17:52 pdf2png

I would expect the go mod download will pull down the necessary packages and allows the build to pass as it is passing in my local without using docker.

I believe the issue is go mod tidy. Your Dockerfile runs this command before any Go source files have been copied to the build container. So Go aggressively tidies go.mod by removing all dependencies.

In this case I think you can just remove the go mod tidy. Especially since this isn't the final build stage in the Dockerfile.