Allow --enable, --enable-all and --fast to coexist.

This is useful to first enable all linters (including fast ones), then
only enable fast linters, then add extra linters. eg.

```
golangci-lint run --no-config --enable-all --fast --print-issued-lines=false \
    --exclude-use-default=false --tests --enable typecheck .
```

Author: alecthomas

pkg/lint/lintersdb/lintersdb.go

@@ -256,7 +256,7 @@ func validateAllDisableEnableOptions(cfg *config.Linters) error {
 		}
 	}
 
-	if cfg.EnableAll && len(cfg.Enable) != 0 {
+	if cfg.EnableAll && len(cfg.Enable) != 0 && !cfg.Fast {
 		return fmt.Errorf("can't combine options --enable-all and --enable %s", cfg.Enable[0])
 	}
 

test/run_test.go

@@ -139,6 +139,19 @@ func getEnabledByDefaultFastLintersExcept(except ...string) []string {
 	return ret
 }
 
+func getAllFastLintersWith(with ...string) []string {
+	linters := lintersdb.GetAllSupportedLinterConfigs()
+	ret := append([]string{}, with...)
+	for _, linter := range linters {
+		if linter.DoesFullImport {
+			continue
+		}
+		ret = append(ret, linter.Linter.Name())
+	}
+
+	return ret
+}
+
 func getEnabledByDefaultLinters() []string {
 	ebdl := lintersdb.GetAllEnabledByDefaultLinters()
 	ret := []string{}
@@ -180,6 +193,15 @@ func mergeMegacheck(linters []string) []string {
 	return linters
 }
 
+func TestEnableAllFastAndEnableCanCoexist(t *testing.T) {
+	out, exitCode := runGolangciLint(t, "--fast", "--enable-all", "--enable=typecheck")
+	checkNoIssuesRun(t, out, exitCode)
+
+	_, exitCode = runGolangciLint(t, "--enable-all", "--enable=typecheck")
+	assert.Equal(t, 3, exitCode)
+
+}
+
 func TestEnabledLinters(t *testing.T) {
 	type tc struct {
 		name           string
@@ -267,6 +289,12 @@ func TestEnabledLinters(t *testing.T) {
 			el:             getEnabledByDefaultLinters(),
 			noImplicitFast: true,
 		},
+		{
+			name:           "fast option combined with enable and enable-all",
+			args:           "--enable-all --fast --enable=typecheck",
+			el:             getAllFastLintersWith("typecheck"),
+			noImplicitFast: true,
+		},
 	}
 
 	for _, c := range cases {