Fix PHP version checking

Separate condition to check both cases if the specified string is a valid version and if it is supported
Remove unsupported versions up to 7.4 from regex

src/Psalm/Internal/Analyzer/ProjectAnalyzer.php

@@ -200,6 +200,10 @@ class ProjectAnalyzer
         UnnecessaryVarAnnotation::class,
     ];
 
+    private const PHP_VERSION_REGEX = '^(0|[1-9]\d*)\.(0|[1-9]\d*)(?:\..*)?$';
+
+    private const PHP_SUPPORTED_VERSIONS_REGEX = '^(7\.4|8\.[012])(\..*)?$';
+
     /**
      * @param array<ReportOptions> $generated_report_options
      */
@@ -1179,10 +1183,27 @@ public function refactorCodeAfterCompletion(array $to_refactor): void
      */
     public function setPhpVersion(string $version, string $source): void
     {
-        if (!preg_match('/^(5\.[456]|7\.[01234]|8\.[012])(\..*)?$/', $version)) {
-            throw new UnexpectedValueException('Expecting a version number in the format x.y');
+        if (!preg_match('/' . self::PHP_VERSION_REGEX . '/', $version)) {
+            fwrite(
+                STDERR,
+                'Expecting a version number in the format x.y or x.y.z'
+                . PHP_EOL,
+            );
+            exit(1);
         }
 
+        if (!preg_match('/' . self::PHP_SUPPORTED_VERSIONS_REGEX . '/', $version)) {
+            fwrite(
+                STDERR,
+                'Psalm requires PHP version ">7.4". The specified version '
+                . $version
+                . " is either not supported or doesn't exist."
+                . PHP_EOL,
+            );
+            exit(1);
+        }
+
+
         [$php_major_version, $php_minor_version] = explode('.', $version);
 
         $php_major_version = (int) $php_major_version;