Add benchmark function for getSnippetHash (#758)

* Add benchmark function for getSnippetHash

* Add Github Action that posts a comparison

* Add value to trigger pipeline

* Remove anchors. Not supported

* oops, fix benchmark

* Implement changes from PR comments

.github/workflows/benchstat-pr.yml

@@ -0,0 +1,75 @@
+name: benchstat
+
+on: [pull_request]
+
+jobs:
+  benchstat:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v3
+        with:
+          go-version: '1.19'
+
+      # Generate benchmark report for main branch
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          ref: main
+      - name: Benchmark
+        run: go test ./... -count=10 -run="^$" -bench=. -benchmem | tee -a bench.txt
+      - name: Upload Benchmark
+        uses: actions/upload-artifact@v3
+        with:
+          name: bench-current
+          path: bench.txt
+
+      # Generate benchmark report for the PR
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Benchmark
+        run: go test ./... -count=10 -run="^$" -bench=. -benchmem | tee -a bench.txt
+      - name: Upload Benchmark
+        uses: actions/upload-artifact@v3
+        with:
+          name: bench-incoming
+          path: bench.txt
+
+      # Compare the two reports
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Install benchstat
+        run: go install golang.org/x/perf/cmd/benchstat@latest
+      - name: Download Incoming
+        uses: actions/download-artifact@v3
+        with:
+          name: bench-incoming
+          path: bench-incoming
+      - name: Download Current
+        uses: actions/download-artifact@v3
+        with:
+          name: bench-current
+          path: bench-current
+      - name: Benchstat Results
+        run: benchstat bench-current/bench.txt bench-incoming/bench.txt | tee -a benchstat.txt
+      - name: Upload benchstat results
+        uses: actions/upload-artifact@v3
+        with:
+          name: benchstat
+          path: benchstat.txt
+      - name: Read benchstat.txt
+        id: benchstat_content
+        uses: juliangruber/read-file-action@v1
+        with:
+          path: ./benchstat.txt
+      - name: Post PR Comment
+        uses: thollander/actions-comment-pull-request@v1
+        with:
+          message: |
+            Benchstat (compared to main):
+            
+            ```
+            ${{ steps.benchstat_content.outputs.content }}
+            ```
+          comment_includes: 'Benchstat (compared to main):'
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

pkg/jsonnet/imports_test.go

@@ -2,6 +2,10 @@ package jsonnet
 
 import (
 	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -23,3 +27,82 @@ func TestTransitiveImports(t *testing.T) {
 		"trees/peach.jsonnet",
 	}, imports)
 }
+
+const testFile = `
+local localImport = <IMPORT>;
+local myFunc = function() <IMPORT>;
+
+{
+	local this = self,
+
+	attribute: {
+		name: 'test',
+		value: self.name,
+		otherValue: 'other ' + self.value,
+	},
+	nested: {
+		nested: {
+			nested: {
+				nested: {
+					nested1: {
+						nested: {
+							nested1: {
+								nested: {
+									attribute: <IMPORT>,
+								},
+							},
+							nested2: {
+								strValue: this.nested.nested.nested,
+							},
+						},
+					},
+					nested2: {
+						intValue: 1,
+						importValue: <IMPORT>,
+					},
+				},
+			},
+		},
+	},
+
+	other: myFunc(),
+	useLocal: localImport,
+}`
+
+func BenchmarkGetSnippetHash(b *testing.B) {
+	// Create a very large and complex project
+	tempDir := b.TempDir()
+
+	var mainContentSplit []string
+	for i := 0; i < 1000; i++ {
+		mainContentSplit = append(mainContentSplit, fmt.Sprintf("(import 'file%d.libsonnet')", i))
+	}
+	require.NoError(b, os.WriteFile(filepath.Join(tempDir, "main.jsonnet"), []byte(strings.Join(mainContentSplit, " + ")), 0644))
+	for i := 0; i < 1000; i++ {
+		err := os.WriteFile(
+			filepath.Join(tempDir, fmt.Sprintf("file%d.libsonnet", i)),
+			[]byte(strings.ReplaceAll(testFile, "<IMPORT>", fmt.Sprintf("import 'file%d.libsonnet'", i+1))),
+			0644,
+		)
+		require.NoError(b, err)
+	}
+	require.NoError(b, os.WriteFile(filepath.Join(tempDir, "file1000.libsonnet"), []byte(`"a string"`), 0644))
+
+	// Create a VM. It's important to reuse the same VM
+	// While there is a caching mechanism that normally shouldn't be shared in a benchmark iteration,
+	// it's useful to evaluate its impact here, because the caching will also improve the evaluation performance afterwards.
+	vm := MakeVM(Opts{ImportPaths: []string{tempDir}})
+	content, err := os.ReadFile(filepath.Join(tempDir, "main.jsonnet"))
+	require.NoError(b, err)
+
+	// Run the benchmark
+	mainPath := filepath.Join(tempDir, "main.jsonnet")
+	c := string(content)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		fileHashes = sync.Map{}
+		hash, err := getSnippetHash(vm, mainPath, c)
+		require.NoError(b, err)
+		require.Equal(b, "XrkW8N2EvkFMvdIuHTsGsQespVUl9_xiFmM7v1mqX5s=", hash)
+	}
+}