fix: do not fail on empty YAML varfiles (#5759)

**What this PR does / why we need it**:

The `js-yaml` parser returns `undefined` instead of an empty object
(`{}`) for empty input files.
So, we handle empty YAML varfiles as empty variable dictionaries to
avoid runtime errors.

This PR also converts `module-varfiles` test project to action-based
configuration.

**Which issue(s) this PR fixes**:

Fixes #5741

core/src/config/base.ts

@@ -583,25 +583,30 @@ export async function loadVarfile({
     const filename = basename(resolvedPath.toLowerCase())
 
     if (filename.endsWith(".json")) {
+      // JSON parser throws a JSON syntax error on completely empty input file,
+      // and returns an empty object for an empty JSON.
       const parsed = JSON.parse(data.toString())
       if (!isPlainObject(parsed)) {
         throw new ConfigurationError({
           message: `Configured variable file ${relPath} must be a valid plain JSON object. Got: ${typeof parsed}`,
         })
       }
-      return parsed
+      return parsed as PrimitiveMap
     } else if (filename.endsWith(".yml") || filename.endsWith(".yaml")) {
-      const parsed = load(data.toString())
+      // YAML parser returns `undefined` for empty files, we interpret that as an empty object.
+      const parsed = load(data.toString()) || {}
       if (!isPlainObject(parsed)) {
         throw new ConfigurationError({
           message: `Configured variable file ${relPath} must be a single plain YAML mapping. Got: ${typeof parsed}`,
         })
       }
       return parsed as PrimitiveMap
     } else {
-      // Note: For backwards-compatibility we fall back on using .env as a default format, and don't specifically
-      // validate the extension for that.
-      return dotenv.parse(await readFile(resolvedPath))
+      // Note: For backwards-compatibility we fall back on using .env as a default format,
+      // and don't specifically validate the extension for that.
+      // The dotenv parser returns an empty object for invalid or empty input file.
+      const parsed = dotenv.parse(data)
+      return parsed as PrimitiveMap
     }
   } catch (error) {
     throw new ConfigurationError({

core/test/data/test-projects/action-varfiles/garden.run-a.default.env

@@ -0,0 +1,2 @@
+c=from-action-varfile
+d=from-action-varfile

core/test/data/test-projects/action-varfiles/garden.yml

@@ -0,0 +1,22 @@
+apiVersion: garden.io/v1
+kind: Project
+name: action-varfiles
+varfile: garden.project.env
+environments:
+  - name: default
+providers:
+  - name: test-plugin
+
+---
+
+kind: Run
+name: run-a
+type: test
+varfiles: ["garden.run-a.${environment.name}.env"]
+variables:
+  b: from-action-vars
+  c: from-action-vars # should be overridden by action-level varfile
+  d: from-action-vars # should be overridden by var passed as a CLI option
+
+spec:
+  command: [echo, A]

core/test/data/test-projects/empty-varfiles/empty-varfile.json

@@ -0,0 +1 @@
+{}

core/test/data/test-projects/empty-varfiles/garden.yml

@@ -0,0 +1,20 @@
+apiVersion: garden.io/v1
+kind: Project
+name: empty-varfiles
+environments:
+  - name: default
+providers:
+  - name: test-plugin
+
+---
+
+kind: Run
+name: run-a
+type: test
+varfiles:
+  - "empty-varfile.env"
+  - "empty-varfile.json"
+  - "empty-varfile.yml"
+
+spec:
+  command: [echo, A]

core/test/unit/src/garden.ts

@@ -56,6 +56,7 @@ import { keyBy, set, mapValues, omit, cloneDeep } from "lodash-es"
 import { joi } from "../../../src/config/common.js"
 import { defaultDotIgnoreFile, makeTempDir } from "../../../src/util/fs.js"
 import fsExtra from "fs-extra"
+
 const { realpath, writeFile, readFile, remove, pathExists, mkdirp, copy } = fsExtra
 import { dedent, deline, randomString, wordWrap } from "../../../src/util/string.js"
 import { getLinkedSources, addLinkedSources } from "../../../src/util/ext-source-util.js"
@@ -384,22 +385,31 @@ describe("Garden", () => {
       })
     })
 
-    it("should respect the module variables < module varfile < CLI var precedence order", async () => {
-      const projectRoot = getDataDir("test-projects", "module-varfiles")
+    it("should respect the action variables < action varfile < CLI var precedence order", async () => {
+      const projectRoot = getDataDir("test-projects", "action-varfiles")
 
       const garden = await makeTestGarden(projectRoot)
       // In the normal flow, `garden.variableOverrides` is populated with variables passed via the `--var` CLI option.
       garden.variableOverrides["d"] = "from-cli-var"
       const graph = await garden.getConfigGraph({ log: garden.log, emit: false })
-      const module = graph.getModule("module-a")
-      expect({ ...garden.variables, ...module.variables }).to.eql({
+      const runAction = graph.getRun("run-a")
+      expect({ ...garden.variables, ...runAction.getVariables() }).to.eql({
         a: "from-project-varfile",
-        b: "from-module-vars",
-        c: "from-module-varfile",
+        b: "from-action-vars",
+        c: "from-action-varfile",
         d: "from-cli-var",
       })
     })
 
+    it("should allow empty varfiles", async () => {
+      const projectRoot = getDataDir("test-projects", "empty-varfiles")
+
+      const garden = await makeTestGarden(projectRoot)
+      const graph = await garden.getConfigGraph({ log: garden.log, emit: false })
+      const runAction = graph.getRun("run-a")
+      expect(runAction.getVariables()).to.eql({})
+    })
+
     it("should throw if project root is not in a git repo root", async () => {
       const dir = await tmp.dir({ unsafeCleanup: true })