fix: don't hide typecheck errors inside diff processor

pkg/result/processors/autogenerated_exclude.go

@@ -53,7 +53,7 @@ func (p *AutogeneratedExclude) Process(issues []result.Issue) ([]result.Issue, e
 func (*AutogeneratedExclude) Finish() {}
 
 func (p *AutogeneratedExclude) shouldPassIssue(issue *result.Issue) (bool, error) {
-	if issue.FromLinter == "typecheck" {
+	if issue.FromLinter == typeCheckName {
 		// don't hide typechecking errors in generated files: users expect to see why the project isn't compiling
 		return true, nil
 	}

pkg/result/processors/diff.go

@@ -65,6 +65,11 @@ func (p Diff) Process(issues []result.Issue) ([]result.Issue, error) {
 	}
 
 	return transformIssues(issues, func(issue *result.Issue) *result.Issue {
+		if issue.FromLinter == typeCheckName {
+			// Never hide typechecking errors.
+			return issue
+		}
+
 		hunkPos, isNew := c.IsNewIssue(issue)
 		if !isNew {
 			return nil

pkg/result/processors/invalid_issue.go

@@ -23,7 +23,7 @@ func (InvalidIssue) Name() string {
 
 func (p InvalidIssue) Process(issues []result.Issue) ([]result.Issue, error) {
 	tcIssues := filterIssues(issues, func(issue *result.Issue) bool {
-		return issue.FromLinter == "typecheck"
+		return issue.FromLinter == typeCheckName
 	})
 
 	if len(tcIssues) > 0 {

pkg/result/processors/processor.go

@@ -4,6 +4,8 @@ import (
 	"github.com/golangci/golangci-lint/pkg/result"
 )
 
+const typeCheckName = "typecheck"
+
 type Processor interface {
 	Process(issues []result.Issue) ([]result.Issue, error)
 	Name() string