From 96ae0e864c702921d5b96153f766b43a1fcd563b Mon Sep 17 00:00:00 2001
From: Tobias Klauser <tobias@cilium.io>
Date: Tue, 14 Jan 2025 10:54:22 +0100
Subject: [PATCH] Skip linters early if affected package is not imported

Skip the ioreadall, slowg and timeafter linters early if the respective
packages they check for (i.e. io, slog/log, golang.org/x/exp/slog and
time) is not imported by the package that is currently analyzed. This
should reduce linter run time a bit on packages that don't import any of
the checked packages.

Signed-off-by: Tobias Klauser <tobias@cilium.io>
---
 analysisutil/util.go    | 20 ++++++++++++++++++++
 ioreadall/io_readall.go |  6 ++++++
 slowg/slowg.go          |  7 +++++++
 timeafter/time_after.go |  6 ++++++
 4 files changed, 39 insertions(+)
 create mode 100644 analysisutil/util.go

diff --git a/analysisutil/util.go b/analysisutil/util.go
new file mode 100644
index 0000000..8790aa6
--- /dev/null
+++ b/analysisutil/util.go
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Cilium
+
+// Package analysisutil defines helper functions used by more than one linters.
+package analysisutil
+
+import "go/types"
+
+// ImportsPackage reports whether path is imported by pkg.
+//
+// Copied from
+// golang.org/x/tools/go/analysis/passes/internal/analysisutil.Imports.
+func ImportsPackage(pkg *types.Package, path string) bool {
+	for _, imp := range pkg.Imports() {
+		if imp.Path() == path {
+			return true
+		}
+	}
+	return false
+}
diff --git a/ioreadall/io_readall.go b/ioreadall/io_readall.go
index f6a0777..33960ea 100644
--- a/ioreadall/io_readall.go
+++ b/ioreadall/io_readall.go
@@ -12,6 +12,8 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+
+	"github.com/cilium/linters/analysisutil"
 )
 
 const (
@@ -37,6 +39,10 @@ func init() {
 }
 
 func run(pass *analysis.Pass) (interface{}, error) {
+	if !analysisutil.ImportsPackage(pass.Pkg, "io") {
+		return nil, nil // doesn't directly import io package
+	}
+
 	inspct, ok := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 	if !ok {
 		return nil, errors.New("analyzer is not type *inspector.Inspector")
diff --git a/slowg/slowg.go b/slowg/slowg.go
index 20deadf..3afbf64 100644
--- a/slowg/slowg.go
+++ b/slowg/slowg.go
@@ -13,6 +13,8 @@ import (
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
 	"golang.org/x/tools/go/types/typeutil"
+
+	"github.com/cilium/linters/analysisutil"
 )
 
 // Analyzer implements an analysis function that checks for inappropriate use
@@ -26,6 +28,11 @@ var Analyzer = &analysis.Analyzer{
 }
 
 func run(pass *analysis.Pass) (any, error) {
+	if !analysisutil.ImportsPackage(pass.Pkg, "log/slog") &&
+		!analysisutil.ImportsPackage(pass.Pkg, "golang.org/x/exp/slog") {
+		return nil, nil // doesn't directly import slog package
+	}
+
 	inspect, ok := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 	if !ok {
 		return nil, errors.New("require analyzer of type *inspector.Inspector")
diff --git a/timeafter/time_after.go b/timeafter/time_after.go
index 677d60a..e3a5b85 100644
--- a/timeafter/time_after.go
+++ b/timeafter/time_after.go
@@ -13,6 +13,8 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+
+	"github.com/cilium/linters/analysisutil"
 )
 
 const (
@@ -46,6 +48,10 @@ func (v visitor) Visit(node ast.Node) ast.Visitor {
 }
 
 func run(pass *analysis.Pass) (interface{}, error) {
+	if !analysisutil.ImportsPackage(pass.Pkg, "time") {
+		return nil, nil // doesn't directly import time package
+	}
+
 	inspct, ok := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 	if !ok {
 		return nil, errors.New("analyzer is not type *inspector.Inspector")