Report error on circular local dependencies (#731)

If a stack overflow is found during project evaluation, present any
circular imports found in the dependency graph.

pkl-core/src/test/kotlin/org/pkl/core/project/ProjectTest.kt

@@ -21,9 +21,11 @@ import java.util.regex.Pattern
 import org.assertj.core.api.Assertions.assertThat
 import org.assertj.core.api.Assertions.assertThatCode
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
 import org.junit.jupiter.api.io.TempDir
 import org.pkl.commons.test.FileTestUtils
 import org.pkl.commons.test.PackageServer
+import org.pkl.commons.toPath
 import org.pkl.commons.writeString
 import org.pkl.core.*
 import org.pkl.core.evaluatorSettings.PklEvaluatorSettings
@@ -188,4 +190,58 @@ class ProjectTest {
         )
     }
   }
+
+  @Test
+  fun `fails if project has cyclical dependencies`() {
+    val projectPath = javaClass.getResource("projectCycle1/PklProject")!!.toURI().toPath()
+    val e = assertThrows<PklException> { Project.loadFromPath(projectPath) }
+    val cleanMsg = e.message!!.replace(Regex("file:///.*/resources/test"), "file://")
+    assertThat(cleanMsg)
+      .isEqualTo(
+        """
+        –– Pkl Error ––
+        Local project dependencies cannot be circular.
+        
+        Cycle:
+        ┌─>
+        │  file:///org/pkl/core/project/projectCycle2/PklProject
+        │
+        │  file:///org/pkl/core/project/projectCycle3/PklProject
+        └─
+        """
+          .trimIndent()
+      )
+  }
+
+  @Test
+  fun `fails if a project has cyclical dependencies -- multiple cycles found`() {
+    val projectPath = javaClass.getResource("projectCycle4/PklProject")!!.toURI().toPath()
+    val e = assertThrows<PklException> { Project.loadFromPath(projectPath) }
+    val cleanMsg = e.message!!.replace(Regex("file://.*/resources/test"), "file://")
+    assertThat(cleanMsg)
+      .isEqualTo(
+        """
+        –– Pkl Error ––
+        Local project dependencies cannot be circular.
+        
+        The following circular imports were found.
+        Not all of them are necessarily problematic.
+        The problematic cycles are those declared as local dependencies.
+        
+        Cycle 1:
+        ┌─>
+        │  file:///org/pkl/core/project/projectCycle2/PklProject
+        │
+        │  file:///org/pkl/core/project/projectCycle3/PklProject
+        └─
+        
+        Cycle 2:
+        ┌─>
+        │  file:///org/pkl/core/project/projectCycle4/PklProject
+        └─
+        
+        """
+          .trimIndent()
+      )
+  }
 }

pkl-core/src/test/kotlin/org/pkl/core/util/ImportGraphUtilsTest.kt

@@ -0,0 +1,95 @@
+/*
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.util
+
+import java.net.URI
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.pkl.core.ImportGraph
+
+class ImportGraphUtilsTest {
+  @Test
+  fun basic() {
+    val barUri = URI("file:///bar.pkl")
+    val fooUri = URI("file:///foo.pkl")
+    val graph =
+      ImportGraph(
+        mapOf(
+          fooUri to setOf(ImportGraph.Import(barUri)),
+          barUri to setOf(ImportGraph.Import(fooUri))
+        ),
+        // resolved URIs is not important
+        mapOf()
+      )
+    val cycles = ImportGraphUtils.findImportCycles(graph)
+    assertThat(cycles).isEqualTo(listOf(listOf(fooUri, barUri)))
+  }
+
+  @Test
+  fun `two cycles`() {
+    val barUri = URI("file:///bar.pkl")
+    val fooUri = URI("file:///foo.pkl")
+    val bizUri = URI("file:///biz.pkl")
+    val quxUri = URI("file:///qux.pkl")
+    val graph =
+      ImportGraph(
+        mapOf(
+          fooUri to setOf(ImportGraph.Import(barUri)),
+          barUri to setOf(ImportGraph.Import(fooUri)),
+          bizUri to setOf(ImportGraph.Import(quxUri)),
+          quxUri to setOf(ImportGraph.Import(bizUri))
+        ),
+        // resolved URIs is not important
+        mapOf()
+      )
+    val cycles = ImportGraphUtils.findImportCycles(graph)
+    assertThat(cycles).isEqualTo(listOf(listOf(fooUri, barUri), listOf(bizUri, quxUri)))
+  }
+
+  @Test
+  fun `no cycles`() {
+    val barUri = URI("file:///bar.pkl")
+    val fooUri = URI("file:///foo.pkl")
+    val bizUri = URI("file:///biz.pkl")
+    val quxUri = URI("file:///qux.pkl")
+    val graph =
+      ImportGraph(
+        mapOf(
+          barUri to setOf(ImportGraph.Import(fooUri)),
+          fooUri to setOf(ImportGraph.Import(bizUri)),
+          bizUri to setOf(ImportGraph.Import(quxUri)),
+          quxUri to setOf()
+        ),
+        // resolved URIs is not important
+        mapOf()
+      )
+    val cycles = ImportGraphUtils.findImportCycles(graph)
+    assertThat(cycles).isEmpty()
+  }
+
+  @Test
+  fun `self-import`() {
+    val fooUri = URI("file:///foo.pkl")
+    val graph =
+      ImportGraph(
+        mapOf(fooUri to setOf(ImportGraph.Import(fooUri))),
+        // resolved URIs is not important
+        mapOf()
+      )
+    val cycles = ImportGraphUtils.findImportCycles(graph)
+    assertThat(cycles).isEqualTo(listOf(listOf(fooUri)))
+  }
+}

pkl-core/src/test/resources/org/pkl/core/project/projectCycle1/PklProject

@@ -0,0 +1,12 @@
+amends "pkl:Project"
+
+package {
+  name = "projectCycle1"
+  version = "1.0.0"
+  packageZipUrl = "https://bogus.value"
+  baseUri = "package://localhost:0/projectCycle1"
+}
+
+dependencies {
+  ["projectCycle2"] = import("../projectCycle2/PklProject")
+}

pkl-core/src/test/resources/org/pkl/core/project/projectCycle2/PklProject

@@ -0,0 +1,12 @@
+amends "pkl:Project"
+
+package {
+  name = "projectCycle2"
+  version = "1.0.0"
+  packageZipUrl = "https://bogus.value"
+  baseUri = "package://localhost:0/projectCycle2"
+}
+
+dependencies {
+  ["projectCycle3"] = import("../projectCycle3/PklProject")
+}

pkl-core/src/test/resources/org/pkl/core/project/projectCycle3/PklProject

@@ -0,0 +1,12 @@
+amends "pkl:Project"
+
+package {
+  name = "projectCycle3"
+  version = "1.0.0"
+  packageZipUrl = "https://bogus.value"
+  baseUri = "package://localhost:0/projectCycle3"
+}
+
+dependencies {
+  ["projectCycle2"] = import("../projectCycle2/PklProject")
+}

pkl-core/src/test/resources/org/pkl/core/project/projectCycle4/PklProject

@@ -0,0 +1,7 @@
+amends "pkl:Project"
+
+import "PklProject"
+
+dependencies {
+  ["projectCycle1"] = import("../projectCycle1/PklProject")
+}