Allow configuring of symlink resolve behavior

[ricklamers]

Previously discussed in #698. Allow users to configure esbuild to not resolve symlinks. I've created a reproducible use case in this repo: https://github.com/ricklamers/esbuild-symlink-example.

The core issue is that for symlinks that are resolved, the modules it imports have to be co-located at the symlinks's target location instead of at the location where the symlink itself is located.

Relevant quote from the previous issue:

Are there any plans to support something similar to the --preserve-symlinks flag? Without it our build setup doesn't work since it would require having all dependencies of symlinked imports in the real symlinked location (instead of at the location where the symlink itself is located).

Would be greatly appreciated, as esbuild is fantastic. It sets a new standard in front-end build tools.

[kzc]

Similar to rollup:

$ rollup ./src/index.js -p node-resolve,commonjs,terser --preserveSymlinks --silent | node
3

$ rollup ./src/index.js -p node-resolve,commonjs,terser --preserveSymlinks --silent | wc -c
   71099

the patch below allows esbuild to ignore symlink resolution:

$ esbuild ./src/index.js --bundle --minify --preserve-symlinks | node
3

$ esbuild ./src/index.js --bundle --minify --preserve-symlinks | wc -c
   73281

diff --git a/cmd/esbuild/main.go b/cmd/esbuild/main.go
index da73739..4be1c55 100644
--- a/cmd/esbuild/main.go
+++ b/cmd/esbuild/main.go
@@ -27,4 +27,5 @@ var helpText = func(colors logger.Colors) string {
 ` + colors.Bold + `Simple options:` + colors.Default + `
   --bundle              Bundle all dependencies into the output files
+  --preserve-symlinks   Disable symlink resolution for module lookup
   --define:K=V          Substitute K with V while parsing
   --external:M          Exclude module M from the bundle
diff --git a/internal/config/config.go b/internal/config/config.go
index c4a7362..bfa820f 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -161,4 +161,5 @@ const (
 type Options struct {
 	Mode              Mode
+	PreserveSymlinks  bool
 	RemoveWhitespace  bool
 	MinifyIdentifiers bool
diff --git a/internal/resolver/resolver.go b/internal/resolver/resolver.go
index 26becd3..c254030 100644
--- a/internal/resolver/resolver.go
+++ b/internal/resolver/resolver.go
@@ -769,9 +769,11 @@ func (r *resolver) dirInfoUncached(path string) *dirInfo {
 
 		// Make sure "absRealPath" is the real path of the directory (resolving any symlinks)
-		if entry, ok := parentInfo.entries[base]; ok {
-			if symlink := entry.Symlink(r.fs); symlink != "" {
-				info.absRealPath = symlink
-			} else if parentInfo.absRealPath != "" {
-				info.absRealPath = r.fs.Join(parentInfo.absRealPath, base)
+		if (!r.options.PreserveSymlinks) {
+			if entry, ok := parentInfo.entries[base]; ok {
+				if symlink := entry.Symlink(r.fs); symlink != "" {
+					info.absRealPath = symlink
+				} else if parentInfo.absRealPath != "" {
+					info.absRealPath = r.fs.Join(parentInfo.absRealPath, base)
+				}
 			}
 		}
diff --git a/pkg/api/api.go b/pkg/api/api.go
index fe5b8bc..acaeb3d 100644
--- a/pkg/api/api.go
+++ b/pkg/api/api.go
@@ -245,4 +245,5 @@ type BuildOptions struct {
 	GlobalName        string
 	Bundle            bool
+	PreserveSymlinks  bool
 	Splitting         bool
 	Outfile           string
diff --git a/pkg/api/api_impl.go b/pkg/api/api_impl.go
index 0a6b326..86d6f84 100644
--- a/pkg/api/api_impl.go
+++ b/pkg/api/api_impl.go
@@ -617,4 +617,5 @@ func rebuildImpl(
 		Banner:                buildOpts.Banner,
 		Footer:                buildOpts.Footer,
+		PreserveSymlinks:      buildOpts.PreserveSymlinks,
 		WatchMode:             buildOpts.Watch != nil,
 		Plugins:               plugins,
diff --git a/pkg/cli/cli_impl.go b/pkg/cli/cli_impl.go
index 8ef2517..b6f93e5 100644
--- a/pkg/cli/cli_impl.go
+++ b/pkg/cli/cli_impl.go
@@ -39,4 +39,7 @@ func parseOptionsImpl(osArgs []string, buildOpts *api.BuildOptions, transformOpt
 			buildOpts.Bundle = true
 
+		case arg == "--preserve-symlinks" && buildOpts != nil:
+			buildOpts.PreserveSymlinks = true
+
 		case arg == "--splitting" && buildOpts != nil:
 			buildOpts.Splitting = true