[perf] Fix regression (#2079)

## Summary

This is mostly a revert of a few changes made in
3246587
that introduced a perf regression.

## How was it tested?

* builds
* ran `devbox install` on a project that had 2 packages cached in nix
cache and 1 package cached in jetify cache

Author: mikeland73

internal/devpkg/narinfo_cache.go

@@ -86,13 +86,13 @@ func FillNarInfoCache(ctx context.Context, packages ...*Package) error {
 	group, _ := errgroup.WithContext(ctx)
 	for _, p := range eligiblePackages {
 		pkg := p // copy the loop variable since its used in a closure below
-		outputs, err := pkg.GetOutputs()
+		outputNames, err := pkg.GetOutputNames()
 		if err != nil {
 			return err
 		}
 
-		for _, output := range outputs {
-			name := output.Name
+		for _, outputName := range outputNames {
+			name := outputName
 			group.Go(func() error {
 				_, err := pkg.fetchNarInfoStatusOnce(name)
 				return err

internal/devpkg/package.go

@@ -241,13 +241,13 @@ func (p *Package) PatchGlibc() bool {
 // Installables for this package. Installables is a nix concept defined here:
 // https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html#installables
 func (p *Package) Installables() ([]string, error) {
-	outputs, err := p.GetOutputs()
+	outputNames, err := p.GetOutputNames()
 	if err != nil {
 		return nil, err
 	}
 	installables := []string{}
-	for _, output := range outputs {
-		i, err := p.InstallableForOutput(output.Name)
+	for _, outputName := range outputNames {
+		i, err := p.InstallableForOutput(outputName)
 		if err != nil {
 			return nil, err
 		}
@@ -675,17 +675,24 @@ func (p *Package) DocsURL() string {
 	return ""
 }
 
-// GetOutputs returns the nix package outputs. Outputs can be
+// GetOutputNames returns the names of the nix package outputs. Outputs can be
 // specified in devbox.json package fields or as part of the flake reference.
-// If they exist in a cache, the cache URI is non-empty.
-func (p *Package) GetOutputs() ([]Output, error) {
-	defer debug.FunctionTimer().End()
+func (p *Package) GetOutputNames() ([]string, error) {
 	if p.IsRunX() {
-		return nil, nil
+		return []string{}, nil
 	}
 
-	names, err := p.outputs.GetNames(p)
-	if err != nil {
+	return p.outputs.GetNames(p)
+}
+
+// GetOutputsWithCache return outputs and their cache URIs if the package is in the binary cache.
+// n+1 WARNING: This will make an http request if FillNarInfoCache is not called before.
+// Grep note: this is used in flake template
+func (p *Package) GetOutputsWithCache() ([]Output, error) {
+	defer debug.FunctionTimer().End()
+
+	names, err := p.GetOutputNames()
+	if err != nil || len(names) == 0 {
 		return nil, err
 	}
 

internal/shellgen/flake_input.go

@@ -89,19 +89,19 @@ func (f *flakeInput) BuildInputsForSymlinkJoin() ([]*SymlinkJoin, error) {
 			return nil, errors.New("patch_glibc is not yet supported for packages with non-default outputs")
 		}
 
-		outputs, err := pkg.GetOutputs()
+		outputNames, err := pkg.GetOutputNames()
 		if err != nil {
 			return nil, err
 		}
 
 		joins = append(joins, &SymlinkJoin{
 			Name: pkg.String() + "-combined",
-			Paths: lo.Map(outputs, func(output devpkg.Output, _ int) string {
+			Paths: lo.Map(outputNames, func(outputName string, _ int) string {
 				if !f.IsNixpkgs() {
-					return f.Name + "." + attributePath + "." + output.Name
+					return f.Name + "." + attributePath + "." + outputName
 				}
 				parts := strings.Split(attributePath, ".")
-				return f.PkgImportName() + "." + strings.Join(parts[2:], ".") + "." + output.Name
+				return f.PkgImportName() + "." + strings.Join(parts[2:], ".") + "." + outputName
 			}),
 		})
 	}
@@ -229,7 +229,7 @@ func (k *keyedSlice) getOrAppend(key string) *flakeInput {
 // Multiple outputs -> SymlinkJoin.
 // Single or no output -> directly use in buildInputs
 func needsSymlinkJoin(pkg *devpkg.Package) (bool, error) {
-	outputNames, err := pkg.GetOutputs()
+	outputNames, err := pkg.GetOutputNames()
 	if err != nil {
 		return false, err
 	}

internal/shellgen/tmpl/flake_remove_nixpkgs.nix.tmpl

@@ -38,7 +38,7 @@
         devShells.{{ .System }}.default = pkgs.mkShell {
           buildInputs = [
             {{- range $_, $pkg := .Packages }}
-            {{- range $_, $output := $pkg.GetOutputs }}
+            {{- range $_, $output := $pkg.GetOutputsWithCache }}
             {{ if $output.CacheURI -}}
             (builtins.trace "downloading {{ $pkg.Versioned }}" (builtins.fetchClosure {
               {{/*