Fix iterable template replacement

psalm-baseline.xml

@@ -388,7 +388,6 @@
   <file src="src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php">
     <ImpureMethodCall>
       <code>getClassTemplateTypes</code>
-      <code>has</code>
     </ImpureMethodCall>
   </file>
   <file src="src/Psalm/Internal/Type/TypeCombiner.php">

src/Psalm/Internal/Provider/ClassLikeStorageProvider.php

@@ -49,10 +49,14 @@ class ClassLikeStorageProvider
         return self::$storage[$fq_classlike_name_lc];
     }
 
+    /**
+     * @psalm-mutation-free
+     */
     public function has(string $fq_classlike_name): bool
     {
         $fq_classlike_name_lc = strtolower($fq_classlike_name);
 
+        /** @psalm-suppress ImpureStaticProperty Used only for caching */
         return isset(self::$storage[$fq_classlike_name_lc]);
     }
 

src/Psalm/Internal/Type/TemplateStandinTypeReplacer.php

@@ -33,7 +33,6 @@ use Psalm\Type\Atomic\TTemplateParamClass;
 use Psalm\Type\Atomic\TTemplatePropertiesOf;
 use Psalm\Type\Atomic\TTemplateValueOf;
 use Psalm\Type\Union;
-use Throwable;
 
 use function array_fill;
 use function array_keys;
@@ -1233,13 +1232,13 @@ class TemplateStandinTypeReplacer
             $input_type_params = [];
         }
 
-        try {
+        $input_class_storage = $codebase->classlike_storage_provider->has($input_type_part->value)
-            $input_class_storage = $codebase->classlike_storage_provider->get($input_type_part->value);
+            ? $codebase->classlike_storage_provider->get($input_type_part->value)
-            $container_class_storage = $codebase->classlike_storage_provider->get($container_type_part->value);
+            : null;
-            $container_type_params_covariant = $container_class_storage->template_covariants;
+
-        } catch (Throwable $e) {
+        $container_type_params_covariant = $codebase->classlike_storage_provider->has($container_type_part->value)
-            $input_class_storage = null;
+            ? $codebase->classlike_storage_provider->get($container_type_part->value)->template_covariants
-        }
+            : null;
 
         if ($input_type_part->value !== $container_type_part->value
             && $input_class_storage
@@ -1266,8 +1265,12 @@ class TemplateStandinTypeReplacer
 
             $template_extends = $input_class_storage->template_extended_params;
 
-            if (isset($template_extends[$container_type_part->value])) {
+            $container_type_part_value = $container_type_part->value === 'iterable'
-                $params = $template_extends[$container_type_part->value];
+                ? 'Traversable'
+                : $container_type_part->value;
+
+            if (isset($template_extends[$container_type_part_value])) {
+                $params = $template_extends[$container_type_part_value];
 
                 $new_input_params = [];
 

tests/FunctionCallTest.php

@@ -46,6 +46,40 @@ class FunctionCallTest extends TestCase
                     '$genericList===' => 'list{1, 2, 3}',
                 ],
             ],
+            'inferIterableFromTraversable' => [
+                'code' => '<?php
+                    /**
+                     * @return SplFixedArray<string>
+                     */
+                    function getStrings(): SplFixedArray
+                    {
+                        return SplFixedArray::fromArray(["fst", "snd", "thr"]);
+                    }
+                    /**
+                     * @return SplFixedArray<int>
+                     */
+                    function getIntegers(): SplFixedArray
+                    {
+                        return SplFixedArray::fromArray([1, 2, 3]);
+                    }
+                    /**
+                     * @template K
+                     * @template A
+                     * @template B
+                     * @param iterable<K, A> $lhs
+                     * @param iterable<K, B> $rhs
+                     * @return iterable<K, A|B>
+                     */
+                    function mergeIterable(iterable $lhs, iterable $rhs): iterable
+                    {
+                        foreach ($lhs as $k => $v) { yield $k => $v; }
+                        foreach ($rhs as $k => $v) { yield $k => $v; }
+                    }
+                    $iterable = mergeIterable(getStrings(), getIntegers());',
+                'assertions' => [
+                    '$iterable===' => 'iterable<int, int|string>',
+                ],
+            ],
             'countShapedArrays' => [
                 'code' => '<?php
                     /** @var array{a?: int} */