Fix #124: support unparam linter

1. Support unparam linter and fix found issues
2. Replace forked mvdan.cc/lint and mvdan.cc/interfacer with the
upstream ones
3. Minimize forked megacheck: move the most of it's code to this repo
4. Use golang.org/x/tools/go/ssa import path instead of custom fork
paths
5. In golang.org/x/tools/go/{ssa,callgraph} use changed code from
honnef.co/go/tools
6. Add megacheck.check-unexported option: it found some issues in
the repo, fixed them all

Author: jirfag

Diff for: .golangci.example.yml

@@ -36,6 +36,7 @@ run:
     - ".*\\.my\\.go$"
     - lib/bad.go
 
+
 # output configuration options
 output:
   # colored-line-number|line-number|json|tab|checkstyle, default is "colored-line-number"
@@ -47,6 +48,7 @@ output:
   # print linter name in the end of issue text, default is true
   print-linter-name: true
 
+
 # all available settings of specific linters
 linters-settings:
   errcheck:
@@ -107,6 +109,23 @@ linters-settings:
   lll:
     # max line length, lines longer will be reported. Default is 120. '\t' is counted as 1 character.
     line-length: 120
+  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
+  unparam:
+    # call graph construction algorithm (cha, rta). In general, use cha for libraries,
+    # and rta for programs with main packages. Default is cha.
+    algo: cha
+
+    # 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
+
 
 linters:
   enable:
@@ -121,6 +140,7 @@ linters:
     - 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,

Diff for: Gopkg.lock

@@ -1,30 +1,3 @@
-# Gopkg.toml example
-#
-# Refer to https://golang.github.io/dep/docs/Gopkg.toml.html
-# for detailed Gopkg.toml documentation.
-#
-# required = ["github.com/user/thing/cmd/thing"]
-# ignored = ["github.com/user/project/pkgX", "bitbucket.org/user/project/pkgA/pkgY"]
-#
-# [[constraint]]
-#   name = "github.com/user/project"
-#   version = "1.0.0"
-#
-# [[constraint]]
-#   name = "github.com/user/project2"
-#   branch = "dev"
-#   source = "github.com/myfork/project2"
-#
-# [[override]]
-#   name = "github.com/x/y"
-#   version = "2.4.0"
-#
-# [prune]
-#   non-go = false
-#   go-tests = true
-#   unused-packages = true
-
-
 [[constraint]]
   name = "github.com/golangci/revgrep"
   branch = "master"
@@ -52,9 +25,9 @@
   source = "github.com/golangci/dupl"
 
 [[constraint]]
-  name = "mvdan.cc/interfacer"
+  name = "mvdan.cc/unparam"
   branch = "master"
-  source = "github.com/golangci/interfacer"
+  source = "github.com/golangci/unparam"
 
 [[constraint]]
   name = "github.com/GoASTScanner/gas"
@@ -73,10 +46,6 @@
   branch = "master"
   name = "github.com/mitchellh/go-ps"
 
-[[constraint]]
-  branch = "master"
-  name = "github.com/golangci/go-tools"
-
 [[constraint]]
   branch = "master"
   name = "github.com/golangci/unconvert"
@@ -109,10 +78,16 @@
   branch = "master"
   name = "github.com/golangci/ineffassign"
 
-[[override]]
+[[constraint]]
   branch = "master"
-  name = "github.com/golangci/lint"
+  name = "github.com/OpenPeeDeeP/depguard"
 
 [[constraint]]
   branch = "master"
-  name = "github.com/OpenPeeDeeP/depguard"
+  name = "golang.org/x/tools"
+  source = "github.com/golangci/tools"
+
+[[constraint]]
+  branch = "master"
+  name = "honnef.co/go/tools"
+  source = "github.com/golangci/go-tools"

Diff for: Gopkg.toml

@@ -122,6 +122,7 @@ megacheck: 3 sub-linters in one: unused, gosimple and staticcheck [fast: false]
 depguard: Go linter that checks if package imports are in a list of acceptable packages [fast: false]
 misspell: Finds commonly misspelled English words in comments [fast: true]
 lll: Reports long lines [fast: true]
+unparam: Reports unused function parameters [fast: false]
 ```
 
 Pass `-E/--enable` to enable linter and `-D/--disable` to disable:
@@ -229,6 +230,7 @@ golangci-lint linters
 - [depguard](https://github.com/OpenPeeDeeP/depguard) - Go linter that checks if package imports are in a list of acceptable packages
 - [misspell](https://github.com/client9/misspell) - Finds commonly misspelled English words in comments
 - [lll](https://github.com/walle/lll) - Reports long lines
+- [unparam](https://github.com/mvdan/unparam) - Reports unused function parameters
 
 # Configuration
 The config file has lower priority than command-line options. If the same bool/string/int option is provided on the command-line
@@ -363,6 +365,7 @@ run:
     - ".*\\.my\\.go$"
     - lib/bad.go
 
+
 # output configuration options
 output:
   # colored-line-number|line-number|json|tab|checkstyle, default is "colored-line-number"
@@ -374,6 +377,7 @@ output:
   # print linter name in the end of issue text, default is true
   print-linter-name: true
 
+
 # all available settings of specific linters
 linters-settings:
   errcheck:
@@ -434,6 +438,23 @@ linters-settings:
   lll:
     # max line length, lines longer will be reported. Default is 120. '\t' is counted as 1 character.
     line-length: 120
+  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
+  unparam:
+    # call graph construction algorithm (cha, rta). In general, use cha for libraries,
+    # and rta for programs with main packages. Default is cha.
+    algo: cha
+
+    # 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
+
 
 linters:
   enable:
@@ -448,6 +469,7 @@ linters:
     - 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,

Diff for: README.md

@@ -237,7 +237,7 @@ func (e *Executor) runAnalysis(ctx context.Context, args []string) (<-chan resul
 		e.reportData.AddLinter(lc.Linter.Name(), isEnabled, lc.EnabledByDefault)
 	}
 
-	lintCtx, err := lint.LoadContext(ctx, linters, e.cfg, e.log.Child("load"))
+	lintCtx, err := lint.LoadContext(linters, e.cfg, e.log.Child("load"))
 	if err != nil {
 		return nil, err
 	}

Diff for: pkg/commands/run.go

@@ -4,8 +4,6 @@ import (
 	"time"
 )
 
-type OutFormat string
-
 const (
 	OutFormatJSON              = "json"
 	OutFormatLineNumber        = "line-number"
@@ -158,7 +156,12 @@ type LintersSettings struct {
 	Misspell struct {
 		Locale string
 	}
-	Lll LllSettings
+	Unused struct {
+		CheckExported bool `mapstructure:"check-exported"`
+	}
+
+	Lll     LllSettings
+	Unparam UnparamSettings
 }
 
 type LllSettings struct {
@@ -169,6 +172,14 @@ var defaultLintersSettings = LintersSettings{
 	Lll: LllSettings{
 		LineLength: 120,
 	},
+	Unparam: UnparamSettings{
+		Algo: "cha",
+	},
+}
+
+type UnparamSettings struct {
+	CheckExported bool `mapstructure:"check-exported"`
+	Algo          string
 }
 
 type Linters struct {

Diff for: pkg/config/config.go

@@ -216,7 +216,7 @@ func runGoCommand(ctx context.Context, log logutils.Log, args ...string) error {
 	return nil
 }
 
-func (g Govet) runOnSourcePackages(ctx context.Context, lintCtx *linter.Context) ([]govetAPI.Issue, error) {
+func (g Govet) runOnSourcePackages(_ context.Context, lintCtx *linter.Context) ([]govetAPI.Issue, error) {
 	// TODO: check .S asm files: govet can do it if pass dirs
 	var govetIssues []govetAPI.Issue
 	for _, pkg := range lintCtx.Program.InitialPackages() {