feat: implement remote stack imports

errors/errors.go

@@ -456,6 +456,10 @@ var (
 	ErrInvalidAuthSection               = errors.New("invalid auth section")
 	ErrInvalidImportSection             = errors.New("invalid import section")
 	ErrInvalidImport                    = errors.New("invalid import")
+	ErrInvalidRemoteImport              = errors.New("invalid remote import")
+	ErrDownloadRemoteImport             = errors.New("failed to download remote import")
+	ErrCacheDirectoryCreation           = errors.New("failed to create cache directory")
+	ErrClearCache                       = errors.New("failed to clear cache")
 	ErrInvalidOverridesSection          = errors.New("invalid overrides section")
 	ErrInvalidTerraformOverridesSection = errors.New("invalid terraform overrides section")
 	ErrInvalidHelmfileOverridesSection  = errors.New("invalid helmfile overrides section")
@@ -638,6 +642,7 @@ var (
 	ErrCacheLocked    = errors.New("cache file is locked")
 	ErrCacheRead      = errors.New("cache read failed")
 	ErrCacheWrite     = errors.New("cache write failed")
+	ErrCacheFetch     = errors.New("failed to fetch content for cache")
 	ErrCacheUnmarshal = errors.New("cache unmarshal failed")
 	ErrCacheMarshal   = errors.New("cache marshal failed")
 	ErrCacheDir       = errors.New("cache directory creation failed")

examples/README.md

@@ -40,7 +40,8 @@ Think of each demo folder as representing an example of a standalone repository.
 9.  ├── demo-context/             # Simplify resource naming and tagging with our Terraform context provider.
 10. ├── demo-workflows/           # Automate repetitive tasks with streamlined workflows.
 11. ├── secrets-masking/          # Configure custom patterns and literals for automatic secrets masking in output.
-12. └── stack-names/              # Demonstrate imperative stack naming with explicit 'name' field.
+12. ├── stack-names/              # Demonstrate imperative stack naming with explicit 'name' field.
+13. └── remote-stack-imports/     # Import stack configurations from remote URLs (HTTP, Git, S3, GCS).
 ```
 
 ## Playground

examples/remote-stack-imports/README.md

@@ -0,0 +1,73 @@
+# Remote Stack Imports Example
+
+This example demonstrates how to import stack configurations from remote sources using [go-getter](https://github.com/hashicorp/go-getter) URL schemes.
+
+## Overview
+
+Atmos supports importing stack configurations from various remote sources:
+- **HTTP/HTTPS URLs** - Raw files from web servers
+- **Git repositories** - Using `git::` prefix or platform shorthand
+- **S3 buckets** - Using `s3::` prefix
+- **Google Cloud Storage** - Using `gcs::` prefix
+
+## Example Structure
+
+```
+remote-stack-imports/
+├── atmos.yaml                    # Atmos configuration
+├── components/terraform/myapp/   # Simple mock component
+└── stacks/
+    ├── catalog/base.yaml         # Local base configuration
+    └── deploy/demo.yaml          # Stack with remote imports
+```
+
+## Try It
+
+```bash
+cd examples/remote-stack-imports
+
+# View the stack configuration (includes remote imports)
+atmos describe stacks
+
+# Describe the component
+atmos describe component myapp -s demo
+```
+
+## Remote Import Examples
+
+### HTTP/HTTPS URL
+
+```yaml
+import:
+  - https://raw.githubusercontent.com/cloudposse/atmos/main/tests/fixtures/remote-imports/shared.yaml
+```
+
+### Git Repository
+
+```yaml
+import:
+  # HTTPS with specific ref
+  - git::https://github.com/acme/infrastructure.git//stacks/catalog/vpc?ref=v1.2.0
+
+  # GitHub shorthand
+  - github.com/acme/infrastructure//stacks/catalog/rds?ref=main
+```
+
+### S3 Bucket
+
+```yaml
+import:
+  - s3::https://s3.amazonaws.com/my-bucket/stacks/catalog/vpc.yaml
+```
+
+## Best Practices
+
+1. **Pin Versions** - Always use `?ref=` with a specific tag or commit SHA for Git imports
+2. **Cache Considerations** - Remote imports are cached locally
+3. **Authentication** - Configure credentials for private repositories via environment variables
+4. **Fallback to Local** - Consider vendoring critical imports for offline access
+
+## Learn More
+
+- [Stack Imports Documentation](https://atmos.tools/stacks/imports)
+- [go-getter URL Formats](https://github.com/hashicorp/go-getter#url-format)

examples/remote-stack-imports/atmos.yaml

@@ -0,0 +1,21 @@
+base_path: "./"
+
+components:
+  terraform:
+    base_path: "components/terraform"
+    apply_auto_approve: false
+    deploy_run_init: true
+    init_run_reconfigure: true
+    auto_generate_backend_file: false
+
+stacks:
+  base_path: "stacks"
+  included_paths:
+    - "deploy/**/*"
+  excluded_paths:
+    - "**/_defaults.yaml"
+  name_template: "{{ .vars.stage }}"
+
+logs:
+  file: "/dev/stderr"
+  level: Info

examples/remote-stack-imports/components/terraform/myapp/main.tf

@@ -0,0 +1,57 @@
+# Mock component for testing remote stack imports.
+# This component doesn't provision any real resources.
+
+variable "name" {
+  type        = string
+  description = "Name of the application"
+  default     = "myapp"
+}
+
+variable "environment" {
+  type        = string
+  description = "Deployment environment"
+  default     = "dev"
+}
+
+variable "imported_from" {
+  type        = string
+  description = "Source of the import (local or remote)"
+  default     = "unknown"
+}
+
+variable "remote_import_test" {
+  type        = bool
+  description = "Flag to indicate this was imported from remote"
+  default     = false
+}
+
+variable "shared_setting" {
+  type        = string
+  description = "A shared setting imported from remote"
+  default     = ""
+}
+
+output "name" {
+  value       = var.name
+  description = "Application name"
+}
+
+output "environment" {
+  value       = var.environment
+  description = "Deployment environment"
+}
+
+output "imported_from" {
+  value       = var.imported_from
+  description = "Import source"
+}
+
+output "remote_import_test" {
+  value       = var.remote_import_test
+  description = "Whether this was imported from remote"
+}
+
+output "shared_setting" {
+  value       = var.shared_setting
+  description = "Shared setting from remote import"
+}

examples/remote-stack-imports/stacks/catalog/base.yaml

@@ -0,0 +1,12 @@
+# Base configuration for the myapp component.
+# This is a local import that provides component defaults.
+
+components:
+  terraform:
+    myapp:
+      metadata:
+        type: abstract
+        component: myapp
+      vars:
+        name: "myapp"
+        environment: "base"

examples/remote-stack-imports/stacks/deploy/demo.yaml

@@ -0,0 +1,31 @@
+# Demo stack that imports from both local and remote sources.
+#
+# This demonstrates the remote stack imports feature:
+# - Local imports work as before (catalog/base)
+# - Remote imports are downloaded via go-getter and merged
+#
+# Note: The remote import URL points to a fixture file in the atmos repo.
+# This example works once the remote-stack-imports feature is merged to main.
+
+import:
+  # Local import - provides base component configuration
+  - catalog/base
+
+  # Remote import - fetches shared configuration from GitHub
+  # This URL points to the test fixture in the atmos repo
+  - https://raw.githubusercontent.com/cloudposse/atmos/main/tests/fixtures/remote-imports/shared.yaml
+
+vars:
+  stage: demo
+
+components:
+  terraform:
+    myapp:
+      metadata:
+        type: real
+      vars:
+        environment: "demo"
+        # These values will be overridden by the remote import:
+        # - imported_from: "remote"
+        # - remote_import_test: true
+        # - shared_setting: "value-from-remote"

examples/remote-stack-imports/stacks/deploy/local-only.yaml

@@ -0,0 +1,18 @@
+# Local-only stack for testing.
+# This stack only uses local imports (no remote).
+
+import:
+  # Local import only
+  - catalog/base
+
+vars:
+  stage: local
+
+components:
+  terraform:
+    myapp:
+      metadata:
+        type: real
+      vars:
+        environment: "local"
+        imported_from: "local"

internal/exec/stack_processor_merge_test.go

@@ -407,15 +407,17 @@ func TestEffectiveAtmosConfig(t *testing.T) {
 	})
 
 	t.Run("later layer wins over earlier layer", func(t *testing.T) {
-		result := effectiveAtmosConfig(base,
+		result := effectiveAtmosConfig(
+			base,
 			map[string]any{"list_merge_strategy": "append"},
 			map[string]any{"list_merge_strategy": "merge"},
 		)
 		assert.Equal(t, "merge", result.Settings.ListMergeStrategy)
 	})
 
 	t.Run("empty string in later layer does not override earlier non-empty value", func(t *testing.T) {
-		result := effectiveAtmosConfig(base,
+		result := effectiveAtmosConfig(
+			base,
 			map[string]any{"list_merge_strategy": "append"},
 			map[string]any{"list_merge_strategy": ""},
 		)