Add golangci-lint to CI

This change introduces the GolangCI linter into the CI, alongside
some sensible defaults for enabled linters.
This should help ensure that we are producing high quality code,
whilst raising potential issues

It is important to note that these configurations are not set in stone,
and are likely to change to suit the workflow of the project, enabling or
disabling behaviour as seen fit.

.circleci/config.yml

@@ -40,6 +40,19 @@ jobs:
           name: Run tests
           command: ginkgo -race -r -v
 
+  lint:
+    <<: *docker_golang
+    steps:
+      - checkout
+      - run:
+          name: Install golangci-lint
+          command: |
+            curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.24.0
+      - run:
+          name: Lint
+          command: |
+            ${GOPATH}/bin/golangci-lint run
+
   build:
     <<: *docker_golang
     steps:
@@ -99,5 +112,6 @@ workflows:
       - check-generated-resources
       - unit-integration
       - build
+      - lint
       - acceptance:
           requires: [build]

.golangci.yml

@@ -0,0 +1,207 @@
+# options for analysis running
+run:
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  timeout: 1m
+
+  # exit code when at least one issue was found, default is 1
+  issues-exit-code: 1
+
+  # include test files or not, default is true
+  tests: true
+
+  # list of build tags, all linters use it. Default is empty list.
+  build-tags: []
+
+  # which dirs to skip: issues from them won't be reported;
+  # can use regexp here: generated.*, regexp is applied on full path;
+  # default value is empty list, but default dirs are skipped independently
+  # from this option's value (see skip-dirs-use-default).
+  skip-dirs: []
+
+  # default is true. Enables skipping of directories:
+  #   vendor$, third_party$, testdata$, examples$, Godeps$, builtin$
+  skip-dirs-use-default: true
+
+  # which files to skip: they will be analyzed, but issues from them
+  # won't be reported. Default value is empty list, but there is
+  # no need to include all autogenerated files, we confidently recognize
+  # autogenerated files. If it's not please let us know.
+  skip-files: []
+
+  # by default isn't set. If set we pass it to "go list -mod={option}". From "go help modules":
+  # If invoked with -mod=readonly, the go command is disallowed from the implicit
+  # automatic updating of go.mod described above. Instead, it fails when any changes
+  # to go.mod are needed. This setting is most useful to check that go.mod does
+  # not need updates, such as in a continuous integration and testing system.
+  # If invoked with -mod=vendor, the go command assumes that the vendor
+  # directory holds the correct copies of dependencies and ignores
+  # the dependency descriptions in go.mod.
+  # modules-download-mode: readonly
+
+
+# output configuration options
+output:
+  # colored-line-number|line-number|json|tab|checkstyle|code-climate, default is "colored-line-number"
+  format: colored-line-number
+
+  # print lines of code with issue, default is true
+  print-issued-lines: true
+
+  # print linter name in the end of issue text, default is true
+  print-linter-name: true
+
+  # make issues output unique by line, default is true
+  uniq-by-line: true
+
+
+# all available settings of specific linters
+linters-settings:
+  dogsled:
+    # checks assignments with too many blank identifiers; default is 2
+    max-blank-identifiers: 2
+  dupl:
+    # tokens count to trigger issue, 150 by default
+    threshold: 100
+  errcheck:
+    # report about not checking of errors in type assertions: `a := b.(MyStruct)`;
+    # default is false: such cases aren't reported by default.
+    check-type-assertions: false
+
+    # report about assignment of errors to blank identifier: `num, _ := strconv.Atoi(numStr)`;
+    # default is false: such cases aren't reported by default.
+    check-blank: false
+  goconst:
+    # minimal length of string constant, 3 by default
+    min-len: 3
+    # minimal occurrences count to trigger, 3 by default
+    min-occurrences: 3
+  godox: {}
+    # report any comments starting with keywords, this is useful for TODO or FIXME comments that
+    # might be left in the code accidentally and should be resolved before merging
+    # keywords: # default keywords are TODO, BUG, and FIXME, these can be overwritten by this setting
+  gofmt:
+    # simplify code: gofmt with `-s` option, true by default
+    simplify: true
+  goimports:
+    # put imports beginning with prefix after 3rd-party packages;
+    # it's a comma-separated list of prefixes
+    local-prefixes: github.com/gocardless/theatre
+  golint:
+    # minimal confidence for issues, default is 0.8
+    min-confidence: 0.8
+  govet:
+    # report about shadowed variables
+    check-shadowing: true
+
+    # enable or disable analyzers by name
+    enable:
+      - atomicalign
+    enable-all: false
+    disable:
+      - shadow
+    disable-all: false
+  maligned:
+    # print struct with more effective memory layout or not, false by default
+    suggest-new: true
+  misspell:
+    # Correct spellings using locale preferences for US or UK.
+    # Default is to use a neutral variety of English.
+    # Setting locale to US will correct the British spelling of 'colour' to 'color'.
+    locale: UK
+    ignore-words: []
+  nakedret:
+    # make an issue if func has more lines of code than this setting and it has naked returns; default is 30
+    max-func-lines: 30
+  unparam:
+    # Inspect exported functions, default is false. Set to true if no external program/library imports your code.
+    # XXX: if you enable this setting, unparam will report a lot of false-positives in text editors:
+    # if it's called for subdir of a project it can't find external interfaces. All text editor integrations
+    # with golangci-lint call it on a directory with the changed file.
+    check-exported: false
+  unused:
+    # treat code as a program (not a library) and report unused exported identifiers; default is false.
+    # XXX: if you enable this setting, unused will report a lot of false-positives in text editors:
+    # if it's called for subdir of a project it can't find funcs usages. All text editor integrations
+    # with golangci-lint call it on a directory with the changed file.
+    check-exported: false
+  whitespace:
+    multi-if: false   # Enforces newlines (or comments) after every multi-line if statement
+    multi-func: false # Enforces newlines (or comments) after every multi-line function signature
+  wsl:
+    # If true append is only allowed to be cuddled if appending value is
+    # matching variables, fields or types on line above. Default is true.
+    strict-append: true
+    # Allow calls and assignments to be cuddled as long as the lines have any
+    # matching variables, fields or types. Default is true.
+    allow-assign-and-call: true
+    # Allow multiline assignments to be cuddled. Default is true.
+    allow-multiline-assign: true
+    # Allow declarations (var) to be cuddled.
+    allow-cuddle-declarations: false
+    # Allow trailing comments in ending of blocks
+    allow-trailing-comment: false
+    # Force newlines in end of case at this limit (0 = never).
+    force-case-trailing-whitespace: 0
+    # Force cuddling of err checks with err var assignment
+    force-err-cuddling: false
+    # Allow leading comments to be separated with empty liens
+    allow-separated-leading-comment: false
+
+linters:
+  enable:
+    - dogsled
+    - gosec
+    - bodyclose
+    - misspell
+    - wsl
+    - whitespace
+    - maligned
+    - megacheck
+    - govet
+  disable-all: false
+  presets:
+    - bugs
+    - unused
+  fast: false
+
+
+issues:
+  # List of regexps of issue texts to exclude, empty list by default.
+  # But independently from this option we use default exclude patterns,
+  # it can be disabled by `exclude-use-default: false`. To list all
+  # excluded by default patterns execute `golangci-lint run --help`
+  exclude:
+    - abcdef
+
+  # Excluding configuration per-path, per-linter, per-text and per-source
+  exclude-rules:
+    # Exclude some linters from running on tests files.
+    - path: _test\.go
+      linters:
+        - gocyclo
+        - errcheck
+        - dupl
+        - gosec
+
+  # Independently from option `exclude` we use default exclude patterns,
+  # it can be disabled by this option. To list all
+  # excluded by default patterns execute `golangci-lint run --help`.
+  # Default value for this option is true.
+  exclude-use-default: false
+
+  # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
+  max-issues-per-linter: 0
+
+  # Maximum count of issues with the same text. Set to 0 to disable. Default is 3.
+  max-same-issues: 0
+
+  # Show only new issues: if there are unstaged changes or untracked files,
+  # only those changes are analyzed, else only changes in HEAD~ are analyzed.
+  # It's a super-useful option for integration of golangci-lint into existing
+  # large codebase. It's not practical to fix all existing issues at the moment
+  # of integration: much better don't allow issues in new code.
+  # Default is false.
+  new: false
+
+  # Show only new issues created after git revision `origin/master`
+  new-from-rev: origin/master