feat: improve docker errors (#3080)

* feat: improve docker errors

Adding an error page with some more info to help debug issues.

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

* fix: forgot return

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

* fix: missing err

Signed-off-by: Carlos A Becker <caarlos0@gmail.com>

internal/pipe/docker/docker.go

@@ -127,7 +127,10 @@ func (Pipe) Run(ctx *context.Context) error {
 			return process(ctx, docker, artifacts.List())
 		})
 	}
-	return g.Wait()
+	if err := g.Wait(); err != nil {
+		return fmt.Errorf("docker build failed: %w\nLearn more at https://goreleaser.com/errors/docker-build\n", err) // nolint:revive
+	}
+	return nil
 }
 
 func process(ctx *context.Context, docker config.Docker, artifacts []*artifact.Artifact) error {

www/docs/errors/docker-build.md

@@ -0,0 +1,60 @@
+# Docker build failures
+
+## `COPY failed: file not found in build context`
+
+This usually happens when trying to build the binary again from source code in
+the Docker image build process.
+
+The way GoReleaser works, the correct binary for the platform you're building
+should be already available, so you don't need to build it again and can still
+reuse the `Dockefile`.
+
+Another common misconception is trying to copy the binary as if the context is
+the repository root.
+It's not.
+It's always a new temporary build context with the artifacts you can use in
+its root, so you can just `COPY binaryname /bin/binaryname` and etc.
+
+Bellow you can find some **don'ts** as well as what you should **do**.
+
+### Don't
+
+Build the binary again.
+
+```dockerfile
+FROM golang AS builder
+WORKDIR /app
+COPY cmd ./cmd
+COPY go.mod ./
+COPY *.go ./
+RUN GOOS=linux GOARCH=amd64 go build -ldflags="-w -s" -o app .
+
+FROM scratch
+COPY --from=builder /app/app /app
+ENTRYPOINT ["/app"]
+```
+
+### Don't
+
+Copy from the `dist` folder.
+
+```dockerfile
+FROM scratch
+COPY /dist/app_linux_amd64/app /app
+ENTRYPOINT ["/app"]
+```
+
+### Do
+
+Copy the clean file names from the root.
+
+```dockerfile
+FROM scratch
+COPY app /app
+ENTRYPOINT ["/app"]
+```
+
+!!! tip
+    If you still want your users to be able to `docker build` without an extra
+    step, you can have a `Dockerfile` just for GoReleaser, for example, a
+    `goreleaser.dockefile`.

www/mkdocs.yml

@@ -134,6 +134,7 @@ nav:
 - Common errors:
   - errors/dirty.md
   - errors/multiple-tokens.md
+  - errors/docker-build.md
   - errors/no-main.md
   - errors/resource-not-accessible-by-integration.md
   - errors/no-history.md