diff --git a/lib/PhpParser/ParserAbstract.php b/lib/PhpParser/ParserAbstract.php
index c31c97a950..dccc5865f6 100644
--- a/lib/PhpParser/ParserAbstract.php
+++ b/lib/PhpParser/ParserAbstract.php
@@ -121,7 +121,7 @@ abstract class ParserAbstract implements Parser {
     /** @var int Error state, used to avoid error floods */
     protected $errorState;
 
-    /** @var \SplObjectStorage Array nodes created during parsing, for postprocessing of empty elements. */
+    /** @var \SplObjectStorage|null Array nodes created during parsing, for postprocessing of empty elements. */
     protected $createdArrays;
 
     /**
diff --git a/lib/PhpParser/PrettyPrinterAbstract.php b/lib/PhpParser/PrettyPrinterAbstract.php
index 1c1876870d..efea814ace 100644
--- a/lib/PhpParser/PrettyPrinterAbstract.php
+++ b/lib/PhpParser/PrettyPrinterAbstract.php
@@ -104,7 +104,7 @@ abstract class PrettyPrinterAbstract {
     /** @var PhpVersion PHP version to target */
     protected $phpVersion;
 
-    /** @var TokenStream Original tokens for use in format-preserving pretty print */
+    /** @var TokenStream|null Original tokens for use in format-preserving pretty print */
     protected $origTokens;
     /** @var Internal\Differ Differ for node lists */
     protected $nodeListDiffer;
@@ -116,9 +116,9 @@ abstract class PrettyPrinterAbstract {
      */
     protected $fixupMap;
     /**
-     * @var int[][] Map from "{$node->getType()}->{$subNode}" to ['left' => $l, 'right' => $r],
-     *              where $l and $r specify the token type that needs to be stripped when removing
-     *              this node.
+     * @var (int|string)[][] Map from "{$node->getType()}->{$subNode}" to ['left' => $l, 'right' => $r],
+     *                       where $l and $r specify the token type that needs to be stripped when
+     *                       removing this node.
      */
     protected $removalMap;
     /**
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
new file mode 100644
index 0000000000..8a04a4721b
--- /dev/null
+++ b/phpstan-baseline.neon
@@ -0,0 +1,141 @@
+parameters:
+	ignoreErrors:
+		-
+			message: "#^Unary operation \"~\" on mixed results in an error\\.$#"
+			count: 1
+			path: lib/PhpParser/ConstExprEvaluator.php
+
+		-
+			message: "#^Unary operation \"\\+\" on string results in an error\\.$#"
+			count: 1
+			path: lib/PhpParser/Lexer/TokenEmulator/NumericLiteralSeparatorEmulator.php
+
+		-
+			message: "#^Access to an undefined property PhpParser\\\\Node\\:\\:\\$attrGroups\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NameResolver.php
+
+		-
+			message: "#^Access to an undefined property PhpParser\\\\Node\\:\\:\\$name\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NameResolver.php
+
+		-
+			message: "#^Access to an undefined property PhpParser\\\\Node\\:\\:\\$namespacedName\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NameResolver.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\NodeConnectingVisitor\\:\\:beforeTraverse\\(\\) should return array\\<PhpParser\\\\Node\\>\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NodeConnectingVisitor.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\NodeConnectingVisitor\\:\\:enterNode\\(\\) should return array\\<PhpParser\\\\Node\\>\\|int\\|PhpParser\\\\Node\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NodeConnectingVisitor.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\NodeConnectingVisitor\\:\\:leaveNode\\(\\) should return array\\<PhpParser\\\\Node\\>\\|int\\|PhpParser\\\\Node\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/NodeConnectingVisitor.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\ParentConnectingVisitor\\:\\:beforeTraverse\\(\\) should return array\\<PhpParser\\\\Node\\>\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/ParentConnectingVisitor.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\ParentConnectingVisitor\\:\\:enterNode\\(\\) should return array\\<PhpParser\\\\Node\\>\\|int\\|PhpParser\\\\Node\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/ParentConnectingVisitor.php
+
+		-
+			message: "#^Method PhpParser\\\\NodeVisitor\\\\ParentConnectingVisitor\\:\\:leaveNode\\(\\) should return array\\<PhpParser\\\\Node\\>\\|int\\|PhpParser\\\\Node\\|null but return statement is missing\\.$#"
+			count: 1
+			path: lib/PhpParser/NodeVisitor/ParentConnectingVisitor.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_AMPERSAND_FOLLOWED_BY_VAR_OR_VARARG\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_AMPERSAND_NOT_FOLLOWED_BY_VAR_OR_VARARG\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_ATTRIBUTE\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_COALESCE_EQUAL\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_ECHO\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_ENUM\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_FN\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_MATCH\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_NAME_FULLY_QUALIFIED\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_NAME_QUALIFIED\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_NAME_RELATIVE\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_NULLSAFE_OBJECT_OPERATOR\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_PAAMAYIM_NEKUDOTAYIM\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Access to undefined constant static\\(PhpParser\\\\ParserAbstract\\)\\:\\:T_READONLY\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Unary operation \"\\+\" on string results in an error\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Variable \\$action might not be defined\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
+
+		-
+			message: "#^Variable \\$tokenValue might not be defined\\.$#"
+			count: 1
+			path: lib/PhpParser/ParserAbstract.php
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000000..e70257c40b
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,7 @@
+includes:
+    - phpstan-baseline.neon
+
+parameters:
+    level: 3
+    paths:
+        - lib