Fix #17, #87: govet becomes SLOW linter by default

1. Allow govet to work in 2 modes: fast and slow. Default is slow.
In fast mode golangci-lint runs `go install -i` and `go test -i`
for analyzed packages. But it's fast only when:
  - go >= 1.10
  - it's repeated run or $GOPATH/pkg or `go env GOCACHE` is cached
  between CI builds
In slow mode we load program from source code like for another linters
and do it only once for all linters.

3. Patch govet code to warn about any troubles with the type
information. Default behaviour of govet was to hide such warnings.
Fail analysis if there are any troubles with type loading: it will
prevent false-positives and false-negatives from govet.

4. Describe almost all options in .golangci.example.yml and
include it into README. Describe when to use slow or fast mode of govet.

5. Speed up govet: reuse AST parsing: it's already parsed once by
golangci-lint.
For "slow" runs (when we run at least one slow linter) speedup by
not loading type information second time.

6. Improve logging, debug logging

Author: jirfag

Diff for: .golangci.example.yml

@@ -1,40 +1,98 @@
+# This file contains all available configuration options
+# with their default values.
+
+# options for analysis running
 run:
+  # default concurrency is a available CPU number
   concurrency: 4
+
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
   deadline: 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:
     - mytag
+
+  # which dirs to skip: they won't be analyzed;
+  # can use regexp here: generated.*, regexp is applied on full path;
+  # default value is empty list, but next dirs are always skipped independently
+  # from this option's value:
+  #   	vendor$, third_party$, testdata$, examples$, Godeps$, builtin$
   skip-dirs:
     - src/external_libs
     - autogenerated_by_my_lib
+
+  # 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:
-    - ".*\\.pb\\.go$"
+    - ".*\\.my\\.go$"
     - lib/bad.go
 
+# output configuration options
 output:
+  # colored-line-number|line-number|json|tab|checkstyle, 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
 
+# all available settings of specific linters
 linters-settings:
   errcheck:
+    # report about not checking of errors in type assetions: `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
   govet:
+    # report about shadowed variables
     check-shadowing: true
+
+    # Obtain type information from installed (to $GOPATH/pkg) package files:
+    # golangci-lint will execute `go install -i` and `go test -i` for analyzed packages
+    # before analyzing them.
+    # By default this option is disabled and govet gets type information by loader from source code.
+    # Loading from source code is slow, but it's done only once for all linters.
+    # Go-installing of packages first time is much slower than loading them from source code,
+    # therefore this option is disabled by default.
+    # But repeated installation is fast in go >= 1.10 because of build caching.
+    # Enable this option only if all conditions are met:
+    #  1. you use only "fast" linters (--fast e.g.): no program loading occurs
+    #  2. you use go >= 1.10
+    #  3. you do repeated runs (false for CI) or cache $GOPATH/pkg or `go env GOCACHE` dir in CI.
+    use-installed-packages: false
   golint:
+    # minimal confidence for issues, default is 0.8
     min-confidence: 0.8
   gofmt:
+    # simplify code: gofmt with `-s` option, true by default
     simplify: true
   gocyclo:
+    # minimal code complexity to report, 30 by default (but we recommend 10-20)
     min-complexity: 10
   maligned:
+    # print struct with more effective memory layout or not, false by default
     suggest-new: true
   dupl:
-    threshold: 50
+    # tokens count to trigger issue, 150 by default
+    threshold: 100
   goconst:
+    # minimal length of string constant, 3 by default
     min-len: 3
+    # minimal occurrences count to trigger, 3 by default
     min-occurrences: 3
   depguard:
     list-type: blacklist
@@ -45,8 +103,8 @@ linters-settings:
 linters:
   enable:
     - megacheck
-    - vet
-  enable-all: true
+    - govet
+  enable-all: false
   disable:
     maligned
   disable-all: false
@@ -56,11 +114,35 @@ linters:
   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
+
+  # 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 false.
   exclude-use-default: true
+
+  # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
   max-per-linter: 0
+
+  # Maximum count of issues with the same text. Set to 0 to disable. Default is 3.
   max-same: 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
-  new-from-rev: ""
-  new-from-patch: ""
+
+  # Show only new issues created after git revision `REV`
+  new-from-rev: REV
+
+  # Show only new issues created in git patch with set file path.
+  new-from-patch: path/to/patch/file

Diff for: Gopkg.lock

@@ -84,7 +84,7 @@ GolangCI-Lint can be used with zero configuration. By default the following lint
 ```
 $ golangci-lint linters
 Enabled by default linters:
-govet: Vet examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string [fast: true]
+govet: Vet examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string [fast: false]
 errcheck: Errcheck is a program for checking for unchecked errors in go programs. These unchecked errors can be critical bugs in some cases [fast: false]
 staticcheck: Staticcheck is a go vet on steroids, applying a ton of static analysis checks [fast: false]
 unused: Checks Go code for unused constants, variables, functions and types [fast: false]
@@ -310,10 +310,161 @@ To see which config file is being used and where it was sourced from run golangc
 Config options inside the file are identical to command-line options.
 You can configure specific linters' options only within the config file (not the command-line).
 
-There is a [`.golangci.yml`](https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml) example config file with all supported options.
+There is a [`.golangci.yml`](https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml) example
+config file with all supported options, their description and default value:
+```yaml
+# This file contains all available configuration options
+# with their default values.
+
+# options for analysis running
+run:
+  # default concurrency is a available CPU number
+  concurrency: 4
+
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  deadline: 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:
+    - mytag
+
+  # which dirs to skip: they won't be analyzed;
+  # can use regexp here: generated.*, regexp is applied on full path;
+  # default value is empty list, but next dirs are always skipped independently
+  # from this option's value:
+  #   	vendor$, third_party$, testdata$, examples$, Godeps$, builtin$
+  skip-dirs:
+    - src/external_libs
+    - autogenerated_by_my_lib
+
+  # 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:
+    - ".*\\.my\\.go$"
+    - lib/bad.go
+
+# output configuration options
+output:
+  # colored-line-number|line-number|json|tab|checkstyle, 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
+
+# all available settings of specific linters
+linters-settings:
+  errcheck:
+    # report about not checking of errors in type assetions: `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
+  govet:
+    # report about shadowed variables
+    check-shadowing: true
+
+    # Obtain type information from installed (to $GOPATH/pkg) package files:
+    # golangci-lint will execute `go install -i` and `go test -i` for analyzed packages
+    # before analyzing them.
+    # By default this option is disabled and govet gets type information by loader from source code.
+    # Loading from source code is slow, but it's done only once for all linters.
+    # Go-installing of packages first time is much slower than loading them from source code,
+    # therefore this option is disabled by default.
+    # But repeated installation is fast in go >= 1.10 because of build caching.
+    # Enable this option only if all conditions are met:
+    #  1. you use only "fast" linters (--fast e.g.): no program loading occurs
+    #  2. you use go >= 1.10
+    #  3. you do repeated runs (false for CI) or cache $GOPATH/pkg or `go env GOCACHE` dir in CI.
+    use-installed-packages: false
+  golint:
+    # minimal confidence for issues, default is 0.8
+    min-confidence: 0.8
+  gofmt:
+    # simplify code: gofmt with `-s` option, true by default
+    simplify: true
+  gocyclo:
+    # minimal code complexity to report, 30 by default (but we recommend 10-20)
+    min-complexity: 10
+  maligned:
+    # print struct with more effective memory layout or not, false by default
+    suggest-new: true
+  dupl:
+    # tokens count to trigger issue, 150 by default
+    threshold: 100
+  goconst:
+    # minimal length of string constant, 3 by default
+    min-len: 3
+    # minimal occurrences count to trigger, 3 by default
+    min-occurrences: 3
+  depguard:
+    list-type: blacklist
+    include-go-root: false
+    packages:
+      - github.com/davecgh/go-spew/spew
+
+linters:
+  enable:
+    - megacheck
+    - govet
+  enable-all: false
+  disable:
+    maligned
+  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
+
+  # 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 false.
+  exclude-use-default: true
+
+  # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
+  max-per-linter: 0
+
+  # Maximum count of issues with the same text. Set to 0 to disable. Default is 3.
+  max-same: 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 `REV`
+  new-from-rev: REV
+
+  # Show only new issues created in git patch with set file path.
+  new-from-patch: path/to/patch/file
+```
 
 It's a [.golangci.yml](https://github.com/golangci/golangci-lint/blob/master/.golangci.yml) config file of this repo: we enable more linters
-than the default and more strict settings:
+than the default and have more strict settings:
 ```yaml
 linters-settings:
   govet:

Diff for: README.md

@@ -200,10 +200,14 @@ To see which config file is being used and where it was sourced from run golangc
 Config options inside the file are identical to command-line options.
 You can configure specific linters' options only within the config file (not the command-line).
 
-There is a [`.golangci.yml`](https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml) example config file with all supported options.
+There is a [`.golangci.yml`](https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml) example
+config file with all supported options, their description and default value:
+```yaml
+{{.GolangciYamlExample}}
+```
 
 It's a [.golangci.yml](https://github.com/golangci/golangci-lint/blob/master/.golangci.yml) config file of this repo: we enable more linters
-than the default and more strict settings:
+than the default and have more strict settings:
 ```yaml
 {{.GolangciYaml}}
 ```

Diff for: README.md.tmpl

@@ -119,7 +119,8 @@ type LintersSettings struct {
 		CheckAssignToBlank  bool `mapstructure:"check-blank"`
 	}
 	Govet struct {
-		CheckShadowing bool `mapstructure:"check-shadowing"`
+		CheckShadowing       bool `mapstructure:"check-shadowing"`
+		UseInstalledPackages bool `mapstructure:"use-installed-packages"`
 	}
 	Golint struct {
 		MinConfidence float64 `mapstructure:"min-confidence"`