Also hint for errors when the root package does not match the constraint

src/Composer/DependencyResolver/Problem.php

@@ -294,6 +294,13 @@ class Problem
                 }
             }
 
+            // check if the root package is a name match and hint the dependencies on root troubleshooting article
+            $allReposPackages = $packages;
+            $topPackage = reset($allReposPackages);
+            if ($topPackage instanceof RootPackageInterface) {
+                $suffix = ' See https://getcomposer.org/dep-on-root for details and assistance.';
+            }
+
             return array("- Root composer.json requires $packageName".self::constraintToText($constraint) . ', ', 'found '.self::getPackageList($packages, $isVerbose).' but '.(self::hasMultipleNames($packages) ? 'these do' : 'it does').' not match the constraint.' . $suffix);
         }
 
@@ -432,7 +439,6 @@ class Problem
         if ($higherRepoPackages) {
             $topPackage = reset($higherRepoPackages);
             if ($topPackage instanceof RootPackageInterface) {
-                $singular = count($nextRepoPackages) === 1;
                 return array(
                     "- Root composer.json requires $packageName".self::constraintToText($constraint).', it is ',
                     'satisfiable by '.self::getPackageList($nextRepoPackages, $isVerbose).' from '.$nextRepo->getRepoName().' but '.$topPackage->getPrettyName().' is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance.'

tests/Composer/Test/Fixtures/installer/circular-dependency-errors.test

@@ -5,7 +5,8 @@ Circular dependencies errors uses helpful message
     "name": "root/pkg",
     "version": "dev-master",
     "require": {
-        "requires/root": "1.0.0"
+        "requires/root": "1.0.0",
+        "requires/root2": "1.0.0"
     },
     "repositories": [
         {
@@ -19,6 +20,14 @@ Circular dependencies errors uses helpful message
                         "root/pkg": "^1.0"
                     }
                 },
+                {
+                    "name": "requires/root2",
+                    "version": "1.0.0",
+                    "source": { "reference": "some.branch", "type": "git", "url": "" },
+                    "require": {
+                        "root/pkg": "^2.0"
+                    }
+                },
                 {
                     "name": "root/pkg",
                     "version": "1.0.0"
@@ -40,6 +49,9 @@ Your requirements could not be resolved to an installable set of packages.
 
   Problem 1
     - Root composer.json requires requires/root 1.0.0 -> satisfiable by requires/root[1.0.0].
-    - requires/root 1.0.0 requires root/pkg ^1.0 -> satisfiable by root/pkg[1.0.0] from package repo (defining 2 packages) but root/pkg is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance.
+    - requires/root 1.0.0 requires root/pkg ^1.0 -> satisfiable by root/pkg[1.0.0] from package repo (defining 3 packages) but root/pkg is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance.
+  Problem 2
+    - Root composer.json requires requires/root2 1.0.0 -> satisfiable by requires/root2[1.0.0].
+    - requires/root2 1.0.0 requires root/pkg ^2.0 -> found root/pkg[dev-master] but it does not match the constraint. See https://getcomposer.org/dep-on-root for details and assistance.
 
 --EXPECT--

tests/Composer/Test/Fixtures/installer/root-alias-change-with-circular-dep.test

@@ -60,6 +60,6 @@ Your lock file does not contain a compatible set of packages. Please run compose
 
   Problem 1
     - b/requirer is locked to version 1.0.0 and an update of this package was not requested.
-    - b/requirer 1.0.0 requires root/pkg ^1 -> found root/pkg[2.x-dev] but it does not match the constraint.
+    - b/requirer 1.0.0 requires root/pkg ^1 -> found root/pkg[2.x-dev] but it does not match the constraint. See https://getcomposer.org/dep-on-root for details and assistance.
 
 --EXPECT--