add .hcl to supported file filter

runatlantis.io/docs/custom-workflows.md

@@ -141,7 +141,7 @@ Given a directory structure:
 .
 ├── live
 │   ├── prod
-│   │   └── terraform.tfvars
+│   │   └── terraform.tfvars     # OR terragrunt.hcl for terragrunt 0.19+ 
 │   └── staging
 │       └── terraform.tfvars
 └── modules
@@ -176,6 +176,41 @@ Atlantis will need to have the `terragrunt` binary in its PATH.
 If you're using Docker you can build your own image, see [Customization](/docs/deployment.html#customization).
 :::
 
+#### Terragrunt Autoplan Configuration
+Since many Terragrunt projects have numerous nested folders where project files reside, 
+updating your repo-level `atlantis.yaml` to include every possible path can be tedious.
+
+Instead, you can use a server-side repo config like this to enable autoplanning of your Terragrunt projects:
+
+```json
+{
+  "repos": [
+    {
+      "id": "/.*/",
+      "workflow": "terragrunt"
+    }
+  ],
+  "workflows": {
+    "terragrunt": {
+      "plan": {
+        "steps": [
+          {
+            "run": "terragrunt plan -no-color -out=$PLANFILE"
+          }
+        ]
+      },
+      "apply": {
+        "steps": [
+          {
+            "run": "terragrunt apply -no-color $PLANFILE"
+          }
+        ]
+      }
+    }
+  }
+}
+```
+
 ### Running custom commands
 Atlantis supports running completely custom commands. In this example, we want to run
 a script after every `apply`:

server/events/project_finder.go

@@ -51,7 +51,7 @@ func (p *DefaultProjectFinder) DetermineProjects(log *logging.SimpleLogger, modi
 	if len(modifiedTerraformFiles) == 0 {
 		return projects
 	}
-	log.Info("filtered modified files to %d .tf files: %v",
+	log.Info("filtered modified files to %d .tf or terragrunt.hcl files: %v",
 		len(modifiedTerraformFiles), modifiedTerraformFiles)
 
 	var dirs []string
@@ -123,7 +123,7 @@ func (p *DefaultProjectFinder) filterToTerraform(files []string) []string {
 	for _, fileName := range files {
 		// Filter out tfstate files since they usually checked in by accident
 		// and regardless, they don't affect a plan.
-		if !p.isStatefile(fileName) && strings.Contains(fileName, ".tf") {
+		if !p.isStatefile(fileName) && (strings.Contains(fileName, ".tf") || fileName == "terragrunt.hcl") {
 			filtered = append(filtered, fileName)
 		}
 	}

server/events/project_finder_test.go

@@ -189,6 +189,12 @@ func TestDetermineProjects(t *testing.T) {
 			[]string{},
 			"",
 		},
+		{
+			"Should not ignore terragrunt.hcl files",
+			[]string{"terragrunt.hcl"},
+			[]string{"."},
+			nestedModules2,
+		},
 	}
 	for _, c := range cases {
 		t.Run(c.description, func(t *testing.T) {