[ASTDumper] Don't attempt to compute type USR for ModuleTypes.

`ModuleType`s show up in some rare places, like the left-hand-side of
a `DotSyntaxBaseIgnoredExpr` for a module-qualified function call.
ASTMangler does not support these because they're not real types.

Author: allevato

lib/AST/ASTDumper.cpp

@@ -260,6 +260,12 @@ std::string typeUSR(Type type) {
   if (!type)
     return "";
 
+  if (type->is<ModuleType>()) {
+    // ASTMangler does not support "module types". This can appear, for
+    // example, on the left-hand side of a `DotSyntaxBaseIgnoredExpr` for a
+    // module-qualified free function call: `Swift.print()`.
+    return "";
+  }
   if (type->hasArchetype()) {
     type = type->mapTypeOutOfEnvironment();
   }
@@ -280,6 +286,13 @@ std::string declTypeUSR(const ValueDecl *D) {
   if (!D)
     return "";
 
+  if (isa<ModuleDecl>(D)) {
+    // ASTMangler does not support "module types". This can appear, for
+    // example, on the left-hand side of a `DotSyntaxBaseIgnoredExpr` for a
+    // module-qualified free function call: `Swift.print()`.
+    return "";
+  }
+
   std::string usr;
   llvm::raw_string_ostream os(usr);
   if (swift::ide::printDeclTypeUSR(D, os))

test/Frontend/ast-dump-json-no-crash.swift

@@ -484,3 +484,10 @@ dynamic func toBeReplaced(arg: Int) {}
 
 @_dynamicReplacement(for: toBeReplaced(arg:))
 func toReplaceWith(arg: Int) {}
+
+// Regression test: Swift 6.2 and earlier crashed trying to form the type USR
+// of the "module type" of a `DotSyntaxBaseIgnoredExpr` when calling a
+// module-qualified free function.
+func moduleTypeUSRRegressionTest() {
+    Swift.print("")
+}