Draft of simplified dependency patch resolution

src/Capability/Resolver/CoreResolverProvider.php

@@ -16,6 +16,7 @@ public function getResolvers(): array
         return [
             new RootComposer($this->composer, $this->io, $this->plugin),
             new PatchesFile($this->composer, $this->io, $this->plugin),
+            new Dependencies($this->composer, $this->io, $this->plugin),
         ];
     }
 }

src/Plugin/Patches.php

@@ -145,7 +145,11 @@ public function activate(Composer $composer, IOInterface $io): void
             'patches-file' => [
                 'type' => 'string',
                 'default' => 'patches.json',
-            ]
+            ],
+            "ignore-dependency-patches" => [
+                'type' => 'list',
+                'default' => [],
+            ],
         ];
         $this->configure($this->composer->getPackage()->getExtra(), 'composer-patches');
     }

src/Resolver/Dependencies.php

@@ -0,0 +1,54 @@
+<?php
+
+/**
+ * @file
+ * Contains \cweagans\Composer\Resolvers\Dependencies.
+ */
+
+namespace cweagans\Composer\Resolver;
+
+use cweagans\Composer\Patch;
+use cweagans\Composer\PatchCollection;
+
+class Dependencies extends ResolverBase
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function resolve(PatchCollection $collection): void
+    {
+        $locker = $this->composer->getLocker();
+        if (!$locker->isLocked()) {
+            $this->io->write('  - <info>Composer lock file does not exist.</info>');
+            $this->io->write('  - <info>Patches defined in dependencies will not be resolved.</info>');
+            return;
+        }
+
+        $this->io->write('  - <info>Resolving patches from dependencies.</info>');
+
+        $ignored_dependencies = $this->plugin->getConfig('ignore-dependency-patches');
+
+        $lockdata = $locker->getLockData();
+        foreach ($lockdata['packages'] as $p) {
+            // If we're supposed to skip gathering patches from a dependency, do that.
+            if (in_array($p['name'], $ignored_dependencies)) {
+                continue;
+            }
+
+            // Find patches in the composer.json for dependencies.
+            if (!isset($p['extra']) || !isset($p['extra']['patches'])) {
+                continue;
+            }
+            foreach ($this->findPatchesInJson($p['extra']['patches']) as $package => $patches) {
+                foreach ($patches as $patch) {
+                    $patch->extra['provenance'] = "dependency:" . $package;
+
+                    /** @var Patch $patch */
+                    $collection->addPatch($patch);
+                }
+            }
+
+            // TODO: Also find patches in a configured patches.json for the dependency.
+        }
+    }
+}

src/Resolver/PatchesFile.php

@@ -32,6 +32,7 @@ public function resolve(PatchCollection $collection): void
         foreach ($this->findPatchesInJson($patches_file) as $package => $patches) {
             foreach ($patches as $patch) {
                 /** @var Patch $patch */
+                $patch->extra['provenance'] = "patches-file:" . $patches_file;
                 $collection->addPatch($patch);
             }
         }

src/Resolver/RootComposer.php

@@ -27,6 +27,7 @@ public function resolve(PatchCollection $collection): void
         foreach ($this->findPatchesInJson($extra['patches']) as $package => $patches) {
             foreach ($patches as $patch) {
                 /** @var Patch $patch */
+                $patch->extra['provenance'] = "root";
                 $collection->addPatch($patch);
             }
         }

tests/_data/dep-test-package/composer.json

@@ -1,16 +1,13 @@
 {
-    "name": "cweagans/dep-test-package",
-    "description": "Project for use in cweagans/composer-patches acceptance tests.",
-    "type": "project",
-    "license": "BSD-2-Clause",
-    "require": {
-        "drupal/drupal": "8.2.0"
-    },
-    "extra": {
-        "patches": {
-            "drupal/drupal": {
-                "Add a startup config for the PHP web server": "https://www.drupal.org/files/issues/add_a_startup-1543858-58.patch"
-            }
-        }
+  "name": "cweagans/dep-test-package",
+  "description": "Project for use in cweagans/composer-patches acceptance tests.",
+  "type": "project",
+  "license": "BSD-3-Clause",
+  "extra": {
+    "patches": {
+      "cweagans/composer-patches-testrepo": {
+        "Add a file": "https://patch-diff.githubusercontent.com/raw/cweagans/composer-patches-testrepo/pull/1.patch"
+      }
     }
+  }
 }

tests/_data/fixtures/dependency-patches/composer.json

@@ -0,0 +1,26 @@
+{
+  "name": "cweagans/composer-patches-test-project",
+  "description": "Project for use in cweagans/composer-patches acceptance tests.",
+  "type": "project",
+  "license": "BSD-3-Clause",
+  "repositories": [
+    {
+      "type": "path",
+      "url": "../../../../"
+    },
+    {
+      "type": "path",
+      "url": "../../dep-test-package"
+    }
+  ],
+  "require": {
+    "cweagans/composer-patches": "*@dev",
+    "cweagans/composer-patches-testrepo": "~1.0",
+    "cweagans/dep-test-package": "*@dev"
+  },
+  "config": {
+    "allow-plugins": {
+      "cweagans/composer-patches": true
+    }
+  }
+}