Loudly reject JSONL on fmt and lint --fix

src/command_fmt.cc

@@ -249,6 +249,12 @@ auto sourcemeta::jsonschema::fmt(const sourcemeta::core::Options &options)
                            entry.resolution_base};
     }
 
+    if (entry.multidocument) {
+      throw MultiDocumentInputError{
+          "This command does not support input with multiple documents",
+          entry.resolution_base};
+    }
+
     if (!entry.second.is_object() && !entry.second.is_boolean()) {
       throw NotSchemaError{entry.resolution_base};
     }

src/command_lint.cc

@@ -491,6 +491,13 @@ auto sourcemeta::jsonschema::lint(const sourcemeta::core::Options &options)
             entry.resolution_base};
       }
 
+      if (entry.multidocument) {
+        throw MultiDocumentInputError{
+            "The --fix option is not supported for input with multiple "
+            "documents",
+            entry.resolution_base};
+      }
+
       if (!entry.second.is_object() && !entry.second.is_boolean()) {
         throw NotSchemaError{entry.resolution_base};
       }

src/error.h

@@ -170,6 +170,20 @@ class YAMLInputError : public std::runtime_error {
   std::filesystem::path path_;
 };
 
+class MultiDocumentInputError : public std::runtime_error {
+public:
+  MultiDocumentInputError(const std::string &message,
+                          std::filesystem::path path)
+      : std::runtime_error{message}, path_{std::move(path)} {}
+
+  [[nodiscard]] auto path() const noexcept -> const std::filesystem::path & {
+    return this->path_;
+  }
+
+private:
+  std::filesystem::path path_;
+};
+
 class UnsupportedOpenAPIFormatError : public std::runtime_error {
 public:
   UnsupportedOpenAPIFormatError()
@@ -1162,6 +1176,10 @@ inline auto try_catch(const sourcemeta::core::Options &options,
     const auto is_json{options.contains("json")};
     print_exception(is_json, error);
     return EXIT_NOT_SUPPORTED;
+  } catch (const MultiDocumentInputError &error) {
+    const auto is_json{options.contains("json")};
+    print_exception(is_json, error);
+    return EXIT_NOT_SUPPORTED;
   } catch (
       const sourcemeta::core::FileError<UnsupportedOpenAPIFormatError> &error) {
     const auto is_json{options.contains("json")};