contrib: add linter to check for panic handler in goroutines

If log.PanicHandler() is not installed in a goroutine and a panic
occurs, the terminal state is not restored. This causes the panic trace
to be unreadable since the terminal is broken.

Add a custom analyzer that parses our code and ensures that:

	defer log.PanicHandler()

is the first statement of all functions that are executed in goroutines.

Include that linter in golangci config.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Bence Ferdinandy <bence@ferdinandy.com>

1 files changed, 128 insertions, 0 deletions

diff --git a/contrib/linters.go b/contrib/linters.go
new file mode 100644
index 00000000..7876cab6
--- /dev/null
+++ b/contrib/linters.go
@@ -0,0 +1,128 @@
+package main
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var PanicAnalyzer = &analysis.Analyzer{
+	Name: "panic",
+	Doc:  "finds goroutines that do not initialize the panic handler",
+	Run:  runPanic,
+}
+
+func runPanic(pass *analysis.Pass) (interface{}, error) {
+	methods := make(map[token.Pos]string)
+	for _, file := range pass.Files {
+		ast.Inspect(file, func(n ast.Node) bool {
+			g, ok := n.(*ast.GoStmt)
+			if !ok {
+				return true
+			}
+
+			var block *ast.BlockStmt
+
+			expr := g.Call.Fun
+			if e, ok := expr.(*ast.ParenExpr); ok {
+				expr = e.X
+			}
+
+			switch e := expr.(type) {
+			case *ast.FuncLit:
+				block = e.Body
+			case *ast.SelectorExpr:
+				sel, ok := pass.TypesInfo.Selections[e]
+				if ok {
+					f, ok := sel.Obj().(*types.Func)
+					if ok {
+						methods[f.Pos()] = f.Name()
+					}
+				}
+			case *ast.Ident:
+				block = inlineFuncBody(e)
+			}
+
+			if block == nil {
+				return true
+			}
+
+			if !isPanicHandlerInstall(block.List[0]) {
+				pass.Report(panicDiag(block.Pos()))
+			}
+
+			return true
+		})
+	}
+	for _, file := range pass.Files {
+		ast.Inspect(file, func(n ast.Node) bool {
+			f, ok := n.(*ast.FuncDecl)
+			if !ok {
+				return false
+			}
+			_, found := methods[f.Name.Pos()]
+			if !found {
+				return false
+			}
+			delete(methods, f.Name.Pos())
+			if !isPanicHandlerInstall(f.Body.List[0]) {
+				pass.Report(panicDiag(f.Body.Pos()))
+			}
+			return false
+		})
+	}
+
+	return nil, nil
+}
+
+func panicDiag(pos token.Pos) analysis.Diagnostic {
+	return analysis.Diagnostic{
+		Pos:      pos,
+		Category: "panic",
+		Message:  "missing defer log.PanicHandler() as first statement",
+	}
+}
+
+func inlineFuncBody(s *ast.Ident) *ast.BlockStmt {
+	d, ok := s.Obj.Decl.(*ast.AssignStmt)
+	if !ok {
+		return nil
+	}
+	for _, r := range d.Rhs {
+		if f, ok := r.(*ast.FuncLit); ok {
+			return f.Body
+		}
+	}
+	return nil
+}
+
+func isPanicHandlerInstall(stmt ast.Stmt) bool {
+	d, ok := stmt.(*ast.DeferStmt)
+	if !ok {
+		return false
+	}
+	s, ok := d.Call.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return false
+	}
+	i, ok := s.X.(*ast.Ident)
+	if !ok {
+		return false
+	}
+	return i.Name == "log" && s.Sel.Name == "PanicHandler"
+}
+
+// golang-lint required plugin api
+type analyzerPlugin struct{}
+
+// This must be implemented
+func (*analyzerPlugin) GetAnalyzers() []*analysis.Analyzer {
+	return []*analysis.Analyzer{
+		PanicAnalyzer,
+	}
+}
+
+// This must be defined and named 'AnalyzerPlugin'
+var AnalyzerPlugin analyzerPlugin