feat(cli): add --stdin-path option

--stdin-path will make it easy to have quick-lint-js detect the
language (JavaScript, TypeScript, etc.) when used from Emacs Flymake
without teaching the ELISP code all language variants (.d.ts, .tsx,
etc.). This feature is similar to ESLint's --stdin-path option.

docs/CHANGELOG.md

@@ -23,6 +23,9 @@ Semantic Versioning.
   is not allowed on getters or setters"). (Implemented by [koopiehoop][].)
 * Emacs: The Debian/Ubuntu package now installs the Emacs plugin. Manual
   installation of the .el files is no longer required.
+* CLI: The new `--stdin-path` CLI option allows users of the `--stdin` option
+  (primarily text editors) to have quick-lint-js detect the language
+  automatically via `--language=default` or `--language=experimental-default`.
 * TypeScript support (still experimental):
   * CLI: The new `--language=experimental-default` option auto-detects
     the language based on `.ts`, `.tsx`, and `.d.ts` in the file path.

docs/cli.adoc

@@ -101,10 +101,43 @@ _path_ does not need to exist in the filesystem.
 Therefore, if multiple input files are given, *--path-for-config-search* can be specified multiple times.
 If *--path-for-config-search* is the last option, it has no effect.
 +
+*--path-for-config-search* overrides *--stdin-path*.
++
 Incompatible with *--lsp-server*.
 +
 Added in quick-lint-js version 0.4.0.
 
+*--stdin-path*=_path_::
+  Change the behavior of *--stdin*.
+*--stdin* still reads a string from standard input, but otherwise it behaves as if the file at _path_ was specified instead:
++
+--
+- The default language is determined by _path_ (unless overridden by *--language*).
+See *--language* for details.
+ifdef::backend-manpage[]
+- Searching for a configuration file
+endif::[]
+ifdef::backend-html5[]
+- link:../config/[Searching for a configuration file]
+endif::[]
+is based on _path_ (unless overridden by *--config-file* or *--path-for-config-file*).
+ifdef::backend-manpage[]
+(See *quick-lint-js.config*(5) for details on configuration file searching.)
+endif::[]
+
+*--stdin-path* applies to only *--stdin*, not file paths (even special files such as /dev/stdin).
+
+*--stdin-path* may appear anywhere in the command line (except after *--*).
+
+_path_ must be a syntactically-valid path.
+_path_ does not need to exist in the filesystem.
+_path_ may be a relative path or an absolute path.
+
+Incompatible with *--lsp-server*.
+
+Added in quick-lint-js version 2.17.0.
+--
+
 [#config-file]
 *--config-file*=_file_::
   Read configuration options from _file_ and apply them to input files which are given later in the command line.
@@ -125,6 +158,8 @@ ifdef::backend-html5[]
 If *--config-file* is not given, *quick-lint-js* link:../config/[searches for a configuration file].
 endif::[]
 +
+*--config-file* overrides *--path-for-config-file* and *--stdin-path*.
++
 Incompatible with *--lsp-server*.
 +
 Added in quick-lint-js version 0.3.0.
@@ -162,6 +197,12 @@ See the <<Example>> section for an example.
 
 If *--language* is the last option, it has no effect.
 
+If the input file is *--stdin*:
+
+- If *--stdin-path* is specified, its _path_ is used for *--language=default*.
+- If *--stdin-path* is not specified, then the path is assumed to be *example.js*.
+This means that *--language=default* will behave like *--language=javascript-jsx*.
+
 Incompatible with *--lsp-server*.
 
 Added in quick-lint-js version 2.10.0.
@@ -175,18 +216,20 @@ See the <<Error lists>> section for a description of the format for _errors_.
 Incompatible with *--lsp-server*.
 
 *--stdin*::
-  Read standard input as a JavaScript file.
+  Read standard input as an input file.
 +
-If neither *--config-file* nor *--path-for-config-search* is specified, an empty configuration file is assumed.
+If none of *--config-file*, *--path-for-config-search*, or *--stdin-path* are specified, an empty configuration file is assumed.
 If *--config-file* is specified, _file_ is used for linting standard input.
-If *--path-for-config-search* is specified and *--config-file* is not specified,
+If *--config-file* is not specified and either *--stdin-path* or *--path-for-config-search* is specified,
 ifdef::backend-manpage[]
 *quick-lint-js* searches for a configuration file according to the rules specified in *quick-lint-js.config*(5)
 endif::[]
 ifdef::backend-html5[]
 *quick-lint-js* link:../config/[searches for a configuration file]
 endif::[]
-starting from *--path-for-config-search*'s _path_.
+starting from *--stdin-path*'s _path_ or *--path-for-config-search*'s _path_.
++
+If neither *--stdin-path* nor *--language* are specified, the *javascript-jsx* language is used.
 +
 Incompatible with *--lsp-server*.
 +

src/quick-lint-js/cli/main.cpp

@@ -301,7 +301,7 @@ void run(Options o) {
         source.error().print_and_exit();
       }
       Linter_Options lint_options =
-          get_linter_options_from_language(get_language(file));
+          get_linter_options_from_language(get_language(file, o));
       lint_options.print_parser_visits = o.print_parser_visits;
       reporter->set_source(&*source, file);
       parse_and_lint(&*source, *reporter->get(), config->globals(),

src/quick-lint-js/cli/options.cpp

@@ -137,6 +137,10 @@ Options parse_options(int argc, char** argv) {
       next_path_for_config_search = arg_value;
     }
 
+    QLJS_OPTION(const char* arg_value, "--stdin-path"sv) {
+      o.path_for_stdin = arg_value;
+    }
+
     QLJS_OPTION(const char* arg_value, "--vim-file-bufnr"sv) {
       o.has_vim_file_bufnr = true;
       int bufnr;
@@ -177,10 +181,26 @@ Options parse_options(int argc, char** argv) {
   if (next_vim_file_bufnr.number != std::nullopt) {
     o.warning_vim_bufnr_without_file.emplace_back(next_vim_file_bufnr.arg_var);
   }
+  if (o.path_for_stdin != nullptr) {
+    for (File_To_Lint& file : o.files_to_lint) {
+      if (file.path_for_config_search == nullptr) {
+        file.path_for_config_search = o.path_for_stdin;
+      }
+    }
+  }
 
   return o;
 }
 
+bool Options::has_stdin() const {
+  for (const File_To_Lint& file : this->files_to_lint) {
+    if (file.is_stdin) {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool Options::dump_errors(Output_Stream& out) const {
   bool have_errors = false;
   if (this->lsp_server) {
@@ -235,6 +255,11 @@ bool Options::dump_errors(Output_Stream& out) const {
     }
   }
 
+  if (this->path_for_stdin != nullptr && !this->has_stdin()) {
+    out.append_copy(
+        u8"warning: '--stdin-path' has no effect without --stdin\n"_sv);
+  }
+
   for (const auto& option : this->error_unrecognized_options) {
     out.append_copy(u8"error: unrecognized option: "_sv);
     out.append_copy(to_string8_view(option));
@@ -261,8 +286,12 @@ bool Options::dump_errors(Output_Stream& out) const {
   return have_errors;
 }
 
-Resolved_Input_File_Language get_language(const File_To_Lint& file) {
-  return get_language(file.path, file.language);
+Resolved_Input_File_Language get_language(const File_To_Lint& file,
+                                          const Options& options) {
+  const char* path = file.is_stdin && options.path_for_stdin != nullptr
+                         ? options.path_for_stdin
+                         : file.path;
+  return get_language(path, file.language);
 }
 
 Resolved_Input_File_Language get_language(const char* file,

src/quick-lint-js/cli/options.h

@@ -55,10 +55,6 @@ struct File_To_Lint {
   std::optional<int> vim_bufnr;
 };
 
-Resolved_Input_File_Language get_language(const File_To_Lint &file);
-Resolved_Input_File_Language get_language(const char *file,
-                                          Raw_Input_File_Language language);
-
 struct Options {
   bool help = false;
   bool list_debug_apps = false;
@@ -70,6 +66,7 @@ struct Options {
   Option_When diagnostic_hyperlinks = Option_When::auto_;
   std::vector<File_To_Lint> files_to_lint;
   Compiled_Diag_Code_List exit_fail_on;
+  const char *path_for_stdin = nullptr;
 
   std::vector<const char *> error_unrecognized_options;
   std::vector<const char *> warning_vim_bufnr_without_file;
@@ -79,9 +76,16 @@ struct Options {
   bool has_language = false;
   bool has_vim_file_bufnr = false;
 
+  bool has_stdin() const;
+
   bool dump_errors(Output_Stream &) const;
 };
 
+Resolved_Input_File_Language get_language(const File_To_Lint &file,
+                                          const Options &);
+Resolved_Input_File_Language get_language(const char *file,
+                                          Raw_Input_File_Language language);
+
 Options parse_options(int argc, char **argv);
 }
 

test/test-cli.cpp

@@ -201,6 +201,46 @@ TEST_F(Test_CLI, automatically_find_config_file_given_path_for_config_search) {
   EXPECT_EQ(r.exit_status, 0);
 }
 
+TEST_F(Test_CLI, path_for_config_search_affects_stdin_file) {
+  std::string test_directory = this->make_temporary_directory();
+  std::string config_file = test_directory + "/quick-lint-js.config";
+  write_file_or_exit(config_file,
+                     u8R"({"globals":{"myGlobalVariable": true}})"_sv);
+
+  Run_Program_Result r = run_program(
+      {
+          get_quick_lint_js_executable_path(),
+          "--path-for-config-search",
+          test_directory + "/app.js",
+          "--stdin",
+      },
+      Run_Program_Options{
+          .input = u8"console.log(myGlobalVariable);"_sv,
+      });
+  EXPECT_EQ(r.output, u8""_sv);
+  EXPECT_EQ(r.exit_status, 0);
+}
+
+TEST_F(Test_CLI, path_for_stdin_affects_stdin_file_config_search) {
+  std::string test_directory = this->make_temporary_directory();
+  std::string config_file = test_directory + "/quick-lint-js.config";
+  write_file_or_exit(config_file,
+                     u8R"({"globals":{"myGlobalVariable": true}})"_sv);
+
+  Run_Program_Result r = run_program(
+      {
+          get_quick_lint_js_executable_path(),
+          "--stdin-path",
+          test_directory + "/app.js",
+          "--stdin",
+      },
+      Run_Program_Options{
+          .input = u8"console.log(myGlobalVariable);"_sv,
+      });
+  EXPECT_EQ(r.output, u8""_sv);
+  EXPECT_EQ(r.exit_status, 0);
+}
+
 TEST_F(Test_CLI, config_file_parse_error_prevents_lint) {
   std::string test_directory = this->make_temporary_directory();
 
@@ -273,6 +313,50 @@ TEST_F(Test_CLI, errors_for_all_config_files_are_printed) {
       << r.output;
 }
 
+TEST_F(Test_CLI, path_for_stdin_affects_default_language) {
+  {
+    Run_Program_Result r = run_program(
+        {get_quick_lint_js_executable_path(), "--language=experimental-default",
+         "--stdin", "--stdin-path=hello.js"},
+        Run_Program_Options{
+            .input = u8"interface I {}"_sv,
+        });
+    EXPECT_EQ(r.exit_status, 1);
+    EXPECT_THAT(to_string(r.output.string_view()), HasSubstr("E0213"))
+        << "expected \"TypeScript's 'interface' feature is not allowed in "
+           "JavaScript code\"\n"
+        << r.output;
+  }
+
+  {
+    Run_Program_Result r = run_program(
+        {get_quick_lint_js_executable_path(), "--language=experimental-default",
+         "--stdin", "--stdin-path=hello.ts"},
+        Run_Program_Options{
+            .input = u8"interface I {}"_sv,
+        });
+    EXPECT_EQ(r.exit_status, 0);
+    EXPECT_THAT(to_string(r.output.string_view()), Not(HasSubstr("E0213")))
+        << "expected no diagnostics because file should be interpreted as "
+           "TypeScript\n"
+        << r.output;
+  }
+}
+
+TEST_F(Test_CLI, language_overrides_path_for_stdin) {
+  Run_Program_Result r = run_program({get_quick_lint_js_executable_path(),
+                                      "--language=experimental-typescript",
+                                      "--stdin", "--stdin-path=hello.js"},
+                                     Run_Program_Options{
+                                         .input = u8"interface I {}"_sv,
+                                     });
+  EXPECT_EQ(r.exit_status, 0);
+  EXPECT_THAT(to_string(r.output.string_view()), Not(HasSubstr("E0213")))
+      << "expected no diagnostics because file should be interpreted as "
+         "TypeScript\n"
+      << r.output;
+}
+
 TEST_F(Test_CLI, language_javascript) {
   Run_Program_Result r = run_program(
       {get_quick_lint_js_executable_path(), "--language=javascript", "--stdin"},

test/test-options.cpp

@@ -557,20 +557,23 @@ TEST(Test_Options, stdin_file) {
     ASSERT_EQ(o.files_to_lint.size(), 2);
     EXPECT_TRUE(o.files_to_lint[0].is_stdin);
     EXPECT_FALSE(o.has_multiple_stdin);
+    EXPECT_EQ(o.path_for_stdin, nullptr);
   }
 
   {
     Options o = parse_options_no_errors({"one.js", "--stdin"});
     ASSERT_EQ(o.files_to_lint.size(), 2);
     EXPECT_TRUE(o.files_to_lint[1].is_stdin);
     EXPECT_FALSE(o.has_multiple_stdin);
+    EXPECT_EQ(o.path_for_stdin, nullptr);
   }
 
   {
     Options o = parse_options_no_errors({"-"});
     ASSERT_EQ(o.files_to_lint.size(), 1);
     EXPECT_TRUE(o.files_to_lint[0].is_stdin);
     EXPECT_FALSE(o.has_multiple_stdin);
+    EXPECT_EQ(o.path_for_stdin, nullptr);
   }
 }
 
@@ -587,6 +590,57 @@ TEST(Test_Options, is_stdin_emplaced_only_once) {
   }
 }
 
+TEST(Test_Options, path_for_stdin) {
+  {
+    Options o = parse_options_no_errors({"--stdin-path", "a.js", "--stdin"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+    EXPECT_STREQ(o.files_to_lint[0].path_for_config_search, "a.js");
+    EXPECT_STREQ(o.path_for_stdin, "a.js");
+  }
+
+  {
+    Options o = parse_options_no_errors({"--stdin-path=a.js", "--stdin"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+    EXPECT_STREQ(o.files_to_lint[0].path_for_config_search, "a.js");
+    EXPECT_STREQ(o.path_for_stdin, "a.js");
+  }
+
+  // Order does not matter.
+  {
+    Options o = parse_options_no_errors({"--stdin", "--stdin-path=a.js"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+    EXPECT_STREQ(o.files_to_lint[0].path_for_config_search, "a.js");
+    EXPECT_STREQ(o.path_for_stdin, "a.js");
+  }
+
+  // Last --stdin-path option takes effect.
+  {
+    Options o = parse_options_no_errors(
+        {"--stdin-path=a.js", "--stdin-path=b.js", "--stdin"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+    EXPECT_STREQ(o.path_for_stdin, "b.js");
+  }
+
+  // --path-for-config-search overrides --stdin-path.
+  {
+    Options o = parse_options_no_errors(
+        {"--path-for-config-search=pfcs.js", "--stdin", "--stdin-path=pfs.js"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+    EXPECT_STREQ(o.files_to_lint[0].path_for_config_search, "pfcs.js");
+    EXPECT_STREQ(o.path_for_stdin, "pfs.js");
+  }
+
+  {
+    Options o = parse_options({"--stdin-path=a.js", "file.js"});
+    ASSERT_EQ(o.files_to_lint.size(), 1);
+
+    Dumped_Errors errors = dump_errors(o);
+    EXPECT_FALSE(errors.have_errors);
+    EXPECT_EQ(errors.output,
+              u8"warning: '--stdin-path' has no effect without --stdin\n"_sv);
+  }
+}
+
 TEST(Test_Options, print_help) {
   {
     Options o = parse_options_no_errors({"--help"});