tests for solver handling multiple packages with same name and version (

#10110)

Not a case with regular Packagist packages, but some custom installers with custom repos do this, and the current behavior should not randomly change at some point, as that would cause downstream breakage.

tests/Composer/Test/DependencyResolver/SolverTest.php

@@ -175,6 +175,115 @@ public function testSolverInstallWithDepsInOrder()
         ));
     }
 
+    /**
+     * This test covers a particular behavior of the solver related to packages with the same name and version,
+     * but different requirements on other packages.
+     * Imagine you had multiple instances of packages (same name/version) with e.g. different dists depending on what other related package they were "built" for.
+     *
+     * An example people can probably relate to, so it was chosen here for better readability:
+     * - PHP versions 8.0.10 and 7.4.23 could be a package
+     * - ext-foobar 1.0.0 could be a package, but it must be built separately for each PHP x.y series
+     * - thus each of the ext-foobar packages lists the "PHP" package as a dependency
+     *
+     * This is not something that can happen with packages on e.g. Packagist, but custom installers with custom repositories might do something like this;
+     * in fact, some PaaSes do the exact thing above, installing binary builds of PHP and extensions as Composer packages with a custom installer in a separate step before the "userland" `composer install`.
+     * 
+     * If version selectors are sufficiently permissive (e.g. "ourcustom/php":"*", "ourcustom/ext-foobar":"*"), then it may happen that the Solver won't pick the highest possible PHP version, as it has already settled on an "ext-foobar" (they're all the same version to the Solver, it doesn't know about the different requirements in each of the otherwise identical packages) if that was listed in "require" before "php".
+     * That's "unfixable", and not even broken, behavior (what if the "ext-foobar" has higher versions for the lower "PHP"? who wins then? any combination of the packages is "correct"), but it shouldn't randomly change.
+     * This test asserts this behavior to prevent regressions.
+     *
+     * CAUTION: IF THIS TEST EVER FAILS, SOLVER BEHAVIOR HAS CHANGED AND MAY BREAK DOWNSTREAM USERS
+     */
+    public function testSolverMultiPackageNameVersionResolutionDependsOnRequireOrder()
+    {
+        $this->repo->addPackage($php74 = $this->getPackage('ourcustom/PHP', '7.4.23'));
+        $this->repo->addPackage($php80 = $this->getPackage('ourcustom/PHP', '8.0.10'));
+        $this->repo->addPackage($extForPhp74 = $this->getPackage('ourcustom/ext-foobar', '1.0'));
+        $this->repo->addPackage($extForPhp80 = $this->getPackage('ourcustom/ext-foobar', '1.0'));
+
+        $extForPhp74->setRequires(array(
+            'php' => new Link('ourcustom/ext-foobar', 'ourcustom/PHP', new MultiConstraint(array(
+                $this->getVersionConstraint('>=', '7.4.0'),
+                $this->getVersionConstraint('<', '7.5.0'),
+            )), Link::TYPE_REQUIRE),
+        ));
+        $extForPhp80->setRequires(array(
+            'php' => new Link('ourcustom/ext-foobar', 'ourcustom/PHP', new MultiConstraint(array(
+                $this->getVersionConstraint('>=', '8.0.0'),
+                $this->getVersionConstraint('<', '8.1.0'),
+            )), Link::TYPE_REQUIRE),
+        ));
+
+        $this->reposComplete();
+
+        $this->request->requireName('ourcustom/PHP');
+        $this->request->requireName('ourcustom/ext-foobar');
+
+        $this->checkSolverResult(array(
+            array('job' => 'install', 'package' => $php80),
+            array('job' => 'install', 'package' => $extForPhp80),
+        ));
+
+        // now we flip the requirements around: we request "ext-foobar" before "php"
+        // because the ext-foobar package that requires php74 comes first in the repo, and the one that requires php80 second, the solver will pick the one for php74, and then, as it is a dependency, also php74
+        // this is because both packages have the same name and version; just their requirements differ
+        // and because no other constraint forces a particular version of package "php"
+        $this->request = new Request($this->repoLocked);
+        $this->request->requireName('ourcustom/ext-foobar');
+        $this->request->requireName('ourcustom/PHP');
+
+        $this->checkSolverResult(array(
+            array('job' => 'install', 'package' => $php74),
+            array('job' => 'install', 'package' => $extForPhp74),
+        ));
+    }
+
+    /**
+     * This test is almost the same as above, except we're inserting the package with the requirement on the other package in a different order, asserting that if that is done, the order of requirements no longer matters
+     *
+     * CAUTION: IF THIS TEST EVER FAILS, SOLVER BEHAVIOR HAS CHANGED AND MAY BREAK DOWNSTREAM USERS
+     */
+    public function testSolverMultiPackageNameVersionResolutionIsIndependentOfRequireOrderIfOrderedDescendingByRequirement()
+    {
+        $this->repo->addPackage($php74 = $this->getPackage('ourcustom/PHP', '7.4'));
+        $this->repo->addPackage($php80 = $this->getPackage('ourcustom/PHP', '8.0'));
+        $this->repo->addPackage($extForPhp80 = $this->getPackage('ourcustom/ext-foobar', '1.0')); // note we are inserting this one into the repo first, unlike in the previous test
+        $this->repo->addPackage($extForPhp74 = $this->getPackage('ourcustom/ext-foobar', '1.0'));
+
+        $extForPhp80->setRequires(array(
+            'php' => new Link('ourcustom/ext-foobar', 'ourcustom/PHP', new MultiConstraint(array(
+                $this->getVersionConstraint('>=', '8.0.0'),
+                $this->getVersionConstraint('<', '8.1.0'),
+            )), Link::TYPE_REQUIRE),
+        ));
+        $extForPhp74->setRequires(array(
+            'php' => new Link('ourcustom/ext-foobar', 'ourcustom/PHP', new MultiConstraint(array(
+                $this->getVersionConstraint('>=', '7.4.0'),
+                $this->getVersionConstraint('<', '7.5.0'),
+            )), Link::TYPE_REQUIRE),
+        ));
+
+        $this->reposComplete();
+
+        $this->request->requireName('ourcustom/PHP');
+        $this->request->requireName('ourcustom/ext-foobar');
+
+        $this->checkSolverResult(array(
+            array('job' => 'install', 'package' => $php80),
+            array('job' => 'install', 'package' => $extForPhp80),
+        ));
+
+        // unlike in the previous test, the order of requirements no longer matters now
+        $this->request = new Request($this->repoLocked);
+        $this->request->requireName('ourcustom/ext-foobar');
+        $this->request->requireName('ourcustom/PHP');
+
+        $this->checkSolverResult(array(
+            array('job' => 'install', 'package' => $php80),
+            array('job' => 'install', 'package' => $extForPhp80),
+        ));
+    }
+
     public function testSolverFixLocked()
     {
         $this->repoLocked->addPackage($packageA = $this->getPackage('A', '1.0'));