Allow executables to be file URIs

Author: bioball

pkl-core/src/main/java/org/pkl/core/externalreader/ExternalReaderProcessImpl.java

@@ -17,6 +17,8 @@
 
 import java.io.IOException;
 import java.lang.ProcessBuilder.Redirect;
+import java.net.URI;
+import java.net.URISyntaxException;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Map;
@@ -86,8 +88,26 @@ public ExternalResourceResolver getResourceResolver(long evaluatorId)
     return ExternalResourceResolver.of(getTransport(), evaluatorId);
   }
 
-  private @Nullable String getExecutablePath(String executable) {
-    if (executable.contains("/") || executable.contains("\"")) {
+  private @Nullable String getExecutablePath(String executable)
+      throws ExternalReaderProcessException {
+    if (IoUtils.isUriLike(executable)) {
+      try {
+        var uri = new URI(executable);
+        if (!uri.getScheme().equalsIgnoreCase("file")) {
+          throw new ExternalReaderProcessException(
+              ErrorMessages.create("cannotSpawnNonFileExecutable", uri));
+        }
+        if (!uri.getPath().startsWith("/")) {
+          throw new ExternalReaderProcessException(
+              ErrorMessages.create("invalidOpaqueFileUri", uri));
+        }
+        return uri.getPath();
+      } catch (URISyntaxException e) {
+        throw new ExternalReaderProcessException(
+            ErrorMessages.create("invalidReaderExecutableUri", executable));
+      }
+    }
+    if (executable.contains("/")) {
       return executable;
     }
     var resolved = IoUtils.findExecutableOnPath(executable);
@@ -116,7 +136,7 @@ private MessageTransport getTransport() throws ExternalReaderProcessException {
     var executable = getExecutablePath(spec.executable());
     if (executable == null) {
       throw new ExternalReaderProcessException(
-          ErrorMessages.create("cannotFindCommand", spec.executable()));
+          ErrorMessages.create("cannotResolveExternalReaderCommand", spec.executable()));
     }
     command.add(executable);
     if (spec.arguments() != null) {

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -1067,6 +1067,17 @@ External {0} reader does not support scheme `{1}`.
 externalReaderAlreadyTerminated=\
 External reader process has already terminated.
 
+cannotSpawnNonFileExecutable=\
+Invalid external reader executable `{0}`.\n\
+\n\
+Executables must be files.
+
+cannotResolveExternalReaderCommand=\
+Cannot resolve external reader executable `{0}`.
+
+invalidReaderExecutableUri=\
+Exernal reader executable URI `{0}` has invalid syntax.
+
 invalidOpaqueFileUri=\
 File URIs must have a path that starts with `/` (e.g. file:/path/to/my_module.pkl).\n\
 To resolve relative paths, remove the scheme prefix (remove "file:").

pkl-core/src/test/files/LanguageSnippetTests/input/projects/badPklProject6/PklProject

@@ -0,0 +1,9 @@
+amends "pkl:Project"
+
+evaluatorSettings {
+  externalModuleReaders {
+    ["foo"] {
+      executable = "qux:/foo"
+    }
+  }
+}

pkl-core/src/test/files/LanguageSnippetTests/input/projects/badPklProject6/bug.pkl

@@ -0,0 +1 @@
+foo = read("foo:bar")

pkl-core/src/test/files/LanguageSnippetTests/input/projects/badPklProject7/PklProject

@@ -0,0 +1,11 @@
+amends "pkl:Project"
+
+projectFileUri = "modulepath:/foo/bar/PklProject"
+
+evaluatorSettings {
+  externalModuleReaders {
+    ["foo"] {
+      executable = "foo/bar"
+    }
+  }
+}

pkl-core/src/test/files/LanguageSnippetTests/input/projects/badPklProject7/bug.pkl

@@ -0,0 +1 @@
+

pkl-core/src/test/files/LanguageSnippetTests/output/projects/badPklProject6/bug.err

@@ -0,0 +1,27 @@
+–– Pkl Error ––
+Type constraint `(this is AbsoluteUri).implies(startsWith("file:/"))` violated.
+Value: "qux:/foo"
+
+xxx | executable: String((this is AbsoluteUri).implies(startsWith("file:/")))
+                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.EvaluatorSettings#ExternalReader.executable (pkl:EvaluatorSettings)
+
+x | executable = "qux:/foo"
+                 ^^^^^^^^^^
+at PklProject#evaluatorSettings.externalModuleReaders["foo"].executable (file:///$snippetsDir/input/projects/badPklProject6/PklProject)
+
+xxx | ?.map((it) -> it.executable)
+                    ^^^^^^^^^^^^^
+at pkl.Project#pathBasedExecutables.<function#1> (pkl:Project)
+
+xxx | it
+      ^^
+at pkl.Project#pathBasedExecutables (pkl:Project)
+
+xxx | pathBasedExecutables(externalModuleReaders).isNotEmpty.implies(isFileBasedProject),
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.Project#evaluatorSettings (pkl:Project)
+
+x | evaluatorSettings {
+    ^^^^^^^^^^^^^^^^^^^
+at PklProject#evaluatorSettings (file:///$snippetsDir/input/projects/badPklProject6/PklProject)

pkl-core/src/test/files/LanguageSnippetTests/output/projects/badPklProject7/bug.err

@@ -0,0 +1,11 @@
+–– Pkl Error ––
+Type constraint `pathBasedExecutables(externalModuleReaders).isNotEmpty.implies(isFileBasedProject)` violated.
+Value: new ModuleClass { externalProperties = ?; env = ?; allowedModules = ?; allowe...
+
+xxx | pathBasedExecutables(externalModuleReaders).isNotEmpty.implies(isFileBasedProject),
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.Project#evaluatorSettings (pkl:Project)
+
+x | evaluatorSettings {
+    ^^^^^^^^^^^^^^^^^^^
+at PklProject#evaluatorSettings (file:///$snippetsDir/input/projects/badPklProject7/PklProject)

pkl-core/src/test/kotlin/org/pkl/core/externalreader/ExternalReaderProcessTest.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright © 2026 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.externalreader
+
+import org.assertj.core.api.Assertions.assertThatCode
+import org.junit.jupiter.api.Test
+import org.pkl.core.evaluatorSettings.PklEvaluatorSettings
+
+class ExternalReaderProcessTest {
+  @Test
+  fun `invalid URI`() {
+    val process =
+      ExternalReaderProcess.of(
+        PklEvaluatorSettings.ExternalReader("qux:/path/to/execuable", listOf())
+      )
+    assertThatCode { process.getModuleResolver(1) }
+      .hasMessageContaining("Invalid external reader executable `qux:/path/to/execuable`")
+  }
+
+  @Test
+  fun `simple name is resolved off path`() {
+    val process = ExternalReaderProcess.of(PklEvaluatorSettings.ExternalReader("foo", listOf()))
+    assertThatCode { process.getModuleResolver(1) }
+      .hasMessageContaining("Cannot resolve external reader executable `foo`.")
+  }
+}

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

@@ -338,7 +338,31 @@ class ProjectTest {
       )
     assertThatCode { Project.load(src) }
       .hasMessageContaining(
-        "Type constraint `(!relativeExecutables(externalModuleReaders).isEmpty).implies(isFileBasedProject)` violated"
+        "Type constraint `pathBasedExecutables(externalModuleReaders).isNotEmpty.implies(isFileBasedProject)` violated."
+      )
+  }
+
+  @Test
+  fun `cannot set non-file URI`() {
+    val src =
+      ModuleSource.text(
+        // language=pkl
+        """
+      amends "pkl:Project"
+      
+      evaluatorSettings {
+        externalModuleReaders {
+          ["foo"] {
+            executable = "qux:///path/to/executable"
+          }
+        }
+      }
+    """
+          .trimIndent()
+      )
+    assertThatCode { Project.load(src) }
+      .hasMessageContaining(
+        "Type constraint `(this is AbsoluteUri).implies(startsWith(\"file:/\"))` violated."
       )
   }
 }