Make sprintf return non-empty-string when possible

stubs/CoreGenericFunctions.phpstub

@@ -1116,7 +1116,13 @@ function preg_quote(string $str, ?string $delimiter = null) : string {}
 /**
  * @psalm-pure
  *
- * @param string|int|float $values
+ * @template TFormat of string
+ * @template TVal of string|int|float
+ * @param TFormat $format
+ * @param TVal $values
+ * @return (TFormat is non-empty-string
+ *      ? (TVal is non-empty-string|int|float ? non-empty-string : string)
+ *      : string)
  *
  * @psalm-flow ($format, $values) -> return
  */

tests/Config/ConfigTest.php

@@ -1461,7 +1461,6 @@ public function pluginRegistersScannerAndAnalyzer(int $flags, ?int $expectedExce
         FileTypeSelfRegisteringPlugin::$names = $names;
         FileTypeSelfRegisteringPlugin::$flags = $flags;
 
-        /** @var non-empty-string $xml */
         $xml = sprintf(
             '<?xml version="1.0"?>
             <psalm><plugins><pluginClass class="%s"/></plugins></psalm>',

tests/Config/PluginTest.php

@@ -801,7 +801,6 @@ public function testAfterAnalysisHooks(): void
 
     public function testPluginFilenameCanBeAbsolute(): void
     {
-        /** @var non-empty-string $xml */
         $xml = sprintf(
             '<?xml version="1.0"?>
             <psalm
@@ -828,7 +827,6 @@ public function testPluginInvalidAbsoluteFilenameThrowsException(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('does-not-exist/plugins/StringChecker.php');
 
-        /** @var non-empty-string $xml */
         $xml = sprintf(
             '<?xml version="1.0"?>
             <psalm

tests/CoreStubsTest.php

@@ -101,5 +101,27 @@ public function providerValidCodeParse(): iterable
             'ignored_issues' => ['RedundantCondition'],
             'php_version' => '8.0',
         ];
+        yield 'sprintf yields a non-empty-string for non-empty-string value' => [
+            'code' => '<?php
+
+            /**
+             * @param non-empty-string $foo
+             * @return non-empty-string
+             */
+            function foo(string $foo): string
+            {
+                return sprintf("%s", $foo);
+            }
+            ',
+        ];
+        yield 'sprintf yields a string for possible empty string param' => [
+            'code' => '<?php
+
+            $a = sprintf("%s", "");
+            ',
+            'assertions' => [
+                '$a===' => 'string',
+            ],
+        ];
     }
 }