Enable development in Codespaces (#84)

* Enable Codespaces - add default Go files

Codespaces[1] allows us to use a remote vscode environment embedded in
the browser in GitHub[1]

This commit adds the pre-built container configuration[2] for Go[3].
We can customise this configuration as we wish in future commits.

[1] https://github.com/features/codespaces/
[2] https://docs.github.com/en/github/developing-online-with-codespaces/configuring-codespaces-for-your-project#using-a-pre-built-container-configuration
[3] https://github.com/microsoft/vscode-dev-containers/tree/master/containers/go

* Suppress/fix devcontainer Dockerfile warnings

These were hadolint warnings, and there were three of them, all on
.devcontainer/Dockerfile#L17:

DL3003 Use WORKDIR to switch to a directory

DL3008 Pin versions in apt get install.
Instead of `apt-get install <package>`
use `apt-get install <package>=<version>`

DL3015 Avoid additional packages by specifying `--no-install-recommends`

Suppressed the warnings apart from the DL3015 one, which was easy to
fix.

Not fixing the other warnings (for now anyway) as this Dockerfile is
code that has been lifted and shifted from the
`.devcontainer/Dockerfile` in:
https://github.com/microsoft/vscode-dev-containers/tree/master/containers/go

* Update module settings to "on" as we use modules

See:
https://dev.to/maelvls/why-is-go111module-everywhere-and-everything-about-go-modules-24k

* Add shellcheck vscode extension to devcontainer

https://www.shellcheck.net/
https://marketplace.visualstudio.com/items?itemName=timonwong.shellcheck

* Use vscode go language server on devcontainer

https://github.com/golang/vscode-go/blob/master/docs/gopls.md

* Stop installing go dependencies on devcontainer

There is no need to install them as we are using go modules - see:
microsoft/vscode-go#2836

* Set vscode editor go tabsize to correct size of 8

See:
microsoft/vscode-go#2479 (comment)

* Use golangci-lint for vscode devcontainer linting

https://github.com/golangci/golangci-lint

* No longer install Guru on devcontainer

It does not support Go modules:
https://github.com/golang/vscode-go/blob/master/docs/tools.md#guru

* Remove unnecessary gorename from devcontainer

Not needed when using go modules and gopls language server:
https://github.com/golang/vscode-go/blob/master/docs/tools.md#gorename

* Remove unnecessary godoctor from devcontainer

It is not needed when using go modules and the gopls language server:
https://github.com/golang/vscode-go/blob/master/docs/tools.md#godoctor

* Remove unnecessary goimports from devcontainer

Imports are instead handled by the gopls language server:
golang/go#33587 (comment)

* Remove unnecessary golint from devcontainer

Not needed as we are using golangci-lint

* Remove unnecessary gotests from devcontainer

gotests autogenerates table tests boilerplate code.  We don't need this
for this project.

* Remove unnecessary goplay module from devcontainer

We don't need this functionality:
https://github.com/haya14busa/goplay/

* Remove unnecessary gometalinter from devcontainer

Not needed as we are using golangci-lint for linting.

* Remove unnecessary impl module from devcontainer

It does not have support for go modules:
golang/go#37537

* Remove unnecessary fillstruct from devcontainer

fillstruct fills a struct literal with default values[1]
This functionality is now available in the gopls language server[2]

[1] https://github.com/davidrjenni/reftools/tree/master/cmd/fillstruct
[2] golang/go#37576 (comment)

* Add comment to explain why gopkgs is still needed

It is still needed even with gopls:
microsoft/vscode-go#3050 (comment)

* Fix installation of golangci-lint on devcontainer

Prior to this commit, vscode was saying "Analysis tools missing" and
prompting to install it.
Fix was to install golangci-lint via go get, as per:
golangci/golangci-lint#1037 (comment)

* Remove unnecessary gogetdoc from devcontainer

Similar functionality is available in the gopls language server:
fatih/vim-go#2808 (comment)

* Remove unnecessary revive linter from devcontainer

We are using golangci-lint for linting, so no need for revive.

* Remove unnecessary go-tools from devcontainer

go-tools primarily contains staticcheck, which we don't need as we are
using golangci-lint for linting.

* Output go version after building devcontainer

Doing this just to provide assurance that the container has started
successfully, after building.

* Move settings which are not container-specific

The guideline for`devcontainer.json` settings is that they should only
contain settings which _must_ be be changed in a container (e.g.
absolute paths)[1].

Moved the other settings to `.vscode/settings.json` so that they are
more visible, and easier to use when working locally (i.e. not in a
container).

[1] microsoft/vscode-remote-release#874 (comment)

* Up tests timeout as tests are slower on container

The tests seem to run much slower (c. 100 seconds compared to c. 50
seconds) when running on a remote container, compared to locally.
Will investigate to see if this is the same when running on Codespaces.

If the tests are taking 100 seconds we may need to create an issue to
speed them up.

* Add recommended vscode go settings

As per the recommendations at:
https://github.com/golang/tools/blob/master/gopls/doc/vscode.md

* Set dark colour theme for vscode in devcontainer

* Set devcontainer vscode to autosave after 500ms

Adding these settings to the devcontainer settings file rather than the
vscode settings file, as we want them to apply at the machine level.

https://code.visualstudio.com/docs/editor/codebasics#_save-auto-save

Author: johnboyes

.devcontainer/Dockerfile

@@ -0,0 +1,65 @@
+#-------------------------------------------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See https://go.microsoft.com/fwlink/?linkid=2090316 for license information.
+#-------------------------------------------------------------------------------------------------------------
+
+FROM golang:1
+
+# This Dockerfile adds a non-root user with sudo access. Use the "remoteUser"
+# property in devcontainer.json to use it. On Linux, the container user's GID/UIDs
+# will be updated to match your local UID/GID (when using the dockerFile property).
+# See https://aka.ms/vscode-remote/containers/non-root-user for details.
+ARG USERNAME=vscode
+ARG USER_UID=1000
+ARG USER_GID=$USER_UID
+
+# Configure apt, install packages and tools
+# hadolint ignore=DL3003,DL3008
+RUN apt-get update \
+    && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends apt-utils dialog 2>&1 \
+    #
+    # Verify git, process tools, lsb-release (common in install instructions for CLIs) installed
+    && apt-get -y install --no-install-recommends git openssh-client less iproute2 procps lsb-release \
+    #
+    # Build Go tools w/module support
+    && mkdir -p /tmp/gotools \
+    && cd /tmp/gotools \
+    && GOPATH=/tmp/gotools GO111MODULE=on go get -v golang.org/x/tools/gopls@latest 2>&1 \
+    && GOPATH=/tmp/gotools GO111MODULE=on go get -v \
+        github.com/mdempsky/gocode@latest \
+        github.com/sqs/goreturns@latest \
+        # gopkgs is still needed even with gopls: https://github.com/microsoft/vscode-go/issues/3050#issuecomment-592263369
+        github.com/uudashr/gopkgs/v2/cmd/gopkgs@latest  \
+        github.com/ramya-rao-a/go-outline@latest  \
+        github.com/acroca/go-symbols@latest  \
+        github.com/rogpeppe/godef@latest  \
+        github.com/fatih/gomodifytags@latest  \
+        github.com/go-delve/delve/cmd/dlv@latest 2>&1 \
+        github.com/golangci/golangci-lint/cmd/[email protected] \
+    #
+    # Build gocode-gomod
+    && GOPATH=/tmp/gotools go get -x -d github.com/stamblerre/gocode 2>&1 \
+    && GOPATH=/tmp/gotools go build -o gocode-gomod github.com/stamblerre/gocode \
+    #
+    # Install Go tools
+    && mv /tmp/gotools/bin/* /usr/local/bin/ \
+    && mv gocode-gomod /usr/local/bin/ \
+    #
+    # Create a non-root user to use if preferred - see https://aka.ms/vscode-remote/containers/non-root-user.
+    && groupadd --gid $USER_GID $USERNAME \
+    && useradd -s /bin/bash --uid $USER_UID --gid $USER_GID -m $USERNAME \
+    # [Optional] Add sudo support
+    && apt-get install -y --no-install-recommends sudo \
+    && echo $USERNAME ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/$USERNAME \
+    && chmod 0440 /etc/sudoers.d/$USERNAME \
+    #
+    # Clean up
+    && apt-get autoremove -y \
+    && apt-get clean -y \
+    && rm -rf /var/lib/apt/lists/* /tmp/gotools
+
+# Update this to "on" or "off" as appropriate
+# Updated from "auto" to "on" as we are using Go modules for this project
+# See https://dev.to/maelvls/why-is-go111module-everywhere-and-everything-about-go-modules-24k
+ENV GO111MODULE=on

.devcontainer/devcontainer.json

@@ -0,0 +1,29 @@
+{
+	"name": "Go",
+	"dockerFile": "Dockerfile",
+	"runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": { 
+		"terminal.integrated.shell.linux": "/bin/bash",
+		"go.gopath": "/go",
+		"workbench.colorTheme": "Default Dark+",
+		"files.autoSave": "afterDelay",
+		"files.autoSaveDelay": 500,
+	},
+	
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"golang.Go",
+		"timonwong.shellcheck"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "go version",
+
+	// Uncomment to connect as a non-root user. See https://aka.ms/vscode-remote/containers/non-root.
+	// "remoteUser": "vscode"
+}

.vscode/settings.json

@@ -1,4 +1,38 @@
 {
-    "go.testTimeout": "90s",
-    "go.testEnvFile": "${workspaceFolder}/.env"
+    "go.useLanguageServer": true,
+    "[go]": {
+        "editor.tabSize": 8,
+        "editor.formatOnSave": true,
+        "editor.codeActionsOnSave": {
+            "source.organizeImports": true,
+        },
+        // Optional: Disable snippets, as they conflict with completion ranking.
+        "editor.snippetSuggestions": "none",
+    },
+    "[go.mod]": {
+        "editor.formatOnSave": true,
+        "editor.codeActionsOnSave": {
+            "source.organizeImports": true,
+        },
+    },
+    "go.installDependenciesWhenBuilding": false, // the default is only true for backwards compatibility - see https://github.com/microsoft/vscode-go/issues/2836
+    "go.lintTool": "golangci-lint",
+    "go.lintFlags": ["--enable-all","--exclude-use-default=false"],
+    "go.lintOnSave": "file",
+    "go.testTimeout": "240s",
+    "go.testEnvFile": "${workspaceFolder}/.env",
+
+    // "VSCode will complain about the "gopls" settings, but they will still work. 
+    // Once we have a consistent set of settings, we will make the changes in the 
+    // VSCode plugin necessary to remove the errors."
+    // https://github.com/golang/tools/blob/master/gopls/doc/vscode.md
+    "gopls": {
+        // Add parameter placeholders when completing a function.
+       "usePlaceholders": true,
+   
+       // If true, enable additional analyses with staticcheck.
+       // Warning: This will significantly increase memory usage.
+       "staticcheck": false,
+   }
+
 }