Fix #4527 - improve interpolated string types

src/Psalm/Internal/Analyzer/Statements/Expression/EncapsulatedStringAnalyzer.php

@@ -18,7 +18,15 @@ class EncapsulatedStringAnalyzer
     ) : bool {
         $stmt_type = Type::getString();
 
+        $non_empty = false;
+
         foreach ($stmt->parts as $part) {
+            if ($part instanceof PhpParser\Node\Scalar\EncapsedStringPart
+                && $part->value
+            ) {
+                $non_empty = true;
+            }
+
             if (ExpressionAnalyzer::analyze($statements_analyzer, $part, $context) === false) {
                 return false;
             }
@@ -52,6 +60,12 @@ class EncapsulatedStringAnalyzer
             }
         }
 
+        if ($non_empty) {
+            $new_type = new Type\Union([new Type\Atomic\TNonEmptyString()]);
+            $new_type->parent_nodes = $stmt_type->parent_nodes;
+            $stmt_type = $new_type;
+        }
+
         $statements_analyzer->node_data->setType($stmt, $stmt_type);
 
         return true;

tests/BinaryOperationTest.php

@@ -304,6 +304,20 @@ class BinaryOperationTest extends TestCase
                         if (is_int($s)) {}
                     }'
             ],
+            'interpolatedStringNotEmpty' => [
+                '<?php
+                    /**
+                     * @psalm-param non-empty-string $i
+                     */
+                    function func($i): string
+                    {
+                        return $i;
+                    }
+
+                    function foo(string $a) : void {
+                        func("asdasdasd $a");
+                    }'
+            ],
         ];
     }