From b121a5da679f96ec78ce5f199804671ea240fb66 Mon Sep 17 00:00:00 2001
From: Brian Flad <bflad417@gmail.com>
Date: Fri, 6 Mar 2026 14:19:38 -0500
Subject: [PATCH] fix: cache esbuild transform results per VM to avoid repeated
 TTY syscalls

Each call to esbuild.Transform() internally creates a new stderr logger
that unconditionally calls GetTerminalInfo/IoctlGetTermios to check if
stderr is a TTY. Since vm.compile() is called hundreds of times during
generation (once per template rendered plus setup calls), and many calls
receive the same source string, this accumulates significant CPU overhead.

Cache esbuild.TransformResult per VM instance keyed by (name, src) to
avoid redundant transform calls. The cache is bounded by the number of
unique template sources and requires no eviction or synchronization
since VMs are single-goroutine, where the number of template sources is
not likely to be a concern in practice.
---
 internal/vm/vm.go | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/internal/vm/vm.go b/internal/vm/vm.go
index 4589507..0bd4720 100644
--- a/internal/vm/vm.go
+++ b/internal/vm/vm.go
@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/dop251/goja"
@@ -36,10 +37,17 @@ const (
 
 var lineNumberRegex = regexp.MustCompile(` \(*([^ ]+):([0-9]+):([0-9]+)\([0-9]+\)`)
 
+type transformCacheKey struct {
+	name string
+	src  string
+}
+
 // VM is a wrapper around the goja runtime.
 type VM struct {
 	*goja.Runtime
 	globalSourceMapCache map[string]*sourcemap.Consumer
+	transformCache       map[transformCacheKey]*esbuild.TransformResult
+	transformCacheMutex  sync.RWMutex
 }
 
 // Options represents options for running a script.
@@ -82,7 +90,11 @@ func New(randSource RandSource) (*VM, error) {
 		})
 	}
 
-	return &VM{Runtime: g, globalSourceMapCache: make(map[string]*sourcemap.Consumer)}, nil
+	return &VM{
+		Runtime:              g,
+		globalSourceMapCache: make(map[string]*sourcemap.Consumer),
+		transformCache:       make(map[transformCacheKey]*esbuild.TransformResult),
+	}, nil
 }
 
 // Run runs a script in the VM.
@@ -181,14 +193,33 @@ func (v *VM) GetRuntime() *goja.Runtime {
 	return v.Runtime
 }
 
-func (v *VM) compile(name string, src string, strict bool) (*program, error) {
-	// transform src with esbuild -- this ensures we handle typescript
+func (v *VM) cachedTransform(name string, src string) *esbuild.TransformResult {
+	key := transformCacheKey{name: name, src: src}
+
+	v.transformCacheMutex.RLock()
+	if cached, ok := v.transformCache[key]; ok {
+		v.transformCacheMutex.RUnlock()
+		return cached
+	}
+	v.transformCacheMutex.RUnlock()
+
 	result := esbuild.Transform(src, esbuild.TransformOptions{
 		Target:     esbuild.ES2015,
 		Loader:     esbuild.LoaderTS,
 		Sourcemap:  esbuild.SourceMapExternal,
 		Sourcefile: name,
 	})
+
+	v.transformCacheMutex.Lock()
+	v.transformCache[key] = &result
+	v.transformCacheMutex.Unlock()
+
+	return &result
+}
+
+func (v *VM) compile(name string, src string, strict bool) (*program, error) {
+	// transform src with esbuild -- this ensures we handle typescript
+	result := v.cachedTransform(name, src)
 	if len(result.Errors) > 0 {
 		msg := ""
 		for _, errMsg := range result.Errors {