fix(core): fix circular dependency detection

Before this fix, circular build dependencies between modules would
result in an internal error (instead of an informative error message).

core/src/garden.ts

@@ -74,7 +74,7 @@ import { RuntimeContext } from "./runtime-context"
 import { loadPlugins, getDependencyOrder, getModuleTypes } from "./plugins"
 import { deline, naturalList } from "./util/string"
 import { ensureConnected } from "./db/connection"
-import { DependencyValidationGraph } from "./util/validate-dependencies"
+import { cyclesToString, DependencyValidationGraph } from "./util/validate-dependencies"
 import { Profile } from "./util/profiling"
 import { ResolveModuleTask, getResolvedModules, moduleResolutionConcurrencyLimit } from "./tasks/resolve-module"
 import username from "username"
@@ -768,13 +768,15 @@ export class Garden {
     } catch (err) {
       // Wrap the circular dependency error to print a more specific message
       if (err.type === "circular-dependencies") {
-        const cycles = err.cycles.map((c: string[][]) => {
-          // Get the module name of the the cycle (anything else is internal detail as far as users are concerned)
-          return c.map((cycle) => cycle.map((key) => key.split(".")[1]))
-        })
+        // Get the module names from the cycle keys (anything else is internal detail as far as users are concerned)
+        const cycleDescription = cyclesToString([err.detail.cycle.map((key: string) => key.split(".")[1])])
         throw new ConfigurationError(
-          `Detected one or more circular dependencies between module configurations:\n\n${cycles.join("\n")}`,
-          { cycles }
+          dedent`
+            Detected circular dependencies between module configurations:
+
+            ${cycleDescription}
+          `,
+          { cycle: err.detail.cycle }
         )
       } else {
         throw err

core/test/unit/src/garden.ts

@@ -2784,6 +2784,63 @@ describe("Garden", () => {
     })
   })
 
+  describe("getConfigGraph", () => {
+    it("should throw an error if modules have circular build dependencies", async () => {
+      const garden = await TestGarden.factory(pathFoo, {
+        config: {
+          apiVersion: DEFAULT_API_VERSION,
+          kind: "Project",
+          name: "test",
+          path: pathFoo,
+          defaultEnvironment: "default",
+          dotIgnoreFiles: [],
+          environments: [{ name: "default", defaultNamespace, variables: {} }],
+          providers: [],
+          variables: {},
+        },
+      })
+
+      garden.setModuleConfigs([
+        {
+          apiVersion: DEFAULT_API_VERSION,
+          name: "module-a",
+          type: "exec",
+          allowPublish: false,
+          build: { dependencies: [{ name: "module-b", copy: [] }] }, // <----
+          disabled: false,
+          path: pathFoo,
+          serviceConfigs: [],
+          taskConfigs: [],
+          testConfigs: [],
+          spec: {},
+        },
+        {
+          apiVersion: DEFAULT_API_VERSION,
+          name: "module-b",
+          type: "exec",
+          allowPublish: false,
+          build: { dependencies: [{ name: "module-a", copy: [] }] }, // <----
+          disabled: false,
+          path: pathFoo,
+          serviceConfigs: [],
+          taskConfigs: [],
+          testConfigs: [],
+          spec: {},
+        },
+      ])
+
+      await expectError(
+        () => garden.getConfigGraph(garden.log),
+        (err) =>
+          expect(err.message).to.equal(dedent`
+          Detected circular dependencies between module configurations:
+
+          module-a <- module-b <- module-a
+        `)
+      )
+    })
+  })
+
   context("module type has a base", () => {
     it("should throw if the configure handler output doesn't match the module type's base schema", async () => {
       const base = createGardenPlugin({