[clang-doc] Default to Standalone executor and improve documentation

This should provide a more intuitive usage consistent with other tools.

Differential Revision: https://reviews.llvm.org/D130226

clang-tools-extra/clang-doc/tool/ClangDocMain.cpp

@@ -182,12 +182,23 @@ int main(int argc, const char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
   std::error_code OK;
 
-  ExecutorName.setInitialValue("all-TUs");
-  auto Exec = clang::tooling::createExecutorFromCommandLineArgs(
-      argc, argv, ClangDocCategory);
+  const char *Overview =
+    R"(Generates documentation from source code and comments.
 
-  if (!Exec) {
-    llvm::errs() << toString(Exec.takeError()) << "\n";
+Example usage for files without flags (default):
+
+  $ clang-doc File1.cpp File2.cpp ... FileN.cpp
+
+Example usage for a project using a compile commands database:
+
+  $ clang-doc --executor=all-TUs compile_commands.json
+)";
+
+  auto Executor = clang::tooling::createExecutorFromCommandLineArgs(
+      argc, argv, ClangDocCategory, Overview);
+
+  if (!Executor) {
+    llvm::errs() << toString(Executor.takeError()) << "\n";
     return 1;
   }
 
@@ -208,7 +219,7 @@ int main(int argc, const char **argv) {
         ArgAdjuster);
 
   clang::doc::ClangDocContext CDCtx = {
-      Exec->get()->getExecutionContext(),
+      Executor->get()->getExecutionContext(),
       ProjectName,
       PublicOnly,
       OutDirectory,
@@ -239,7 +250,7 @@ int main(int argc, const char **argv) {
   // Mapping phase
   llvm::outs() << "Mapping decls...\n";
   auto Err =
-      Exec->get()->execute(doc::newMapperActionFactory(CDCtx), ArgAdjuster);
+      Executor->get()->execute(doc::newMapperActionFactory(CDCtx), ArgAdjuster);
   if (Err) {
     if (IgnoreMappingFailures)
       llvm::errs() << "Error mapping decls in files. Clang-doc will ignore "
@@ -256,7 +267,7 @@ int main(int argc, const char **argv) {
   // bitcode-encoded representation of the Info object.
   llvm::outs() << "Collecting infos...\n";
   llvm::StringMap<std::vector<StringRef>> USRToBitcode;
-  Exec->get()->getToolResults()->forEachResult(
+  Executor->get()->getToolResults()->forEachResult(
       [&](StringRef Key, StringRef Value) {
         auto R = USRToBitcode.try_emplace(Key, std::vector<StringRef>());
         R.first->second.emplace_back(Value);

clang-tools-extra/docs/ReleaseNotes.rst

@@ -81,7 +81,7 @@ Miscellaneous
 Improvements to clang-doc
 -------------------------
 
-The improvements are...
+- The default executor was changed to standalone to match other tools.
 
 Improvements to clang-query
 ---------------------------

clang-tools-extra/docs/clang-doc.rst

@@ -25,19 +25,23 @@ compile command database for your project (for an example of how to do this
 see `How To Setup Tooling For LLVM
 <https://clang.llvm.org/docs/HowToSetupToolingForLLVM.html>`_).
 
-By default, the tool will run on all files listed in the given compile commands
-database:
+The tool will process a list of files by default:
 
 .. code-block:: console
 
-  $ clang-doc /path/to/compile_commands.json
+  $ clang-doc File1.cpp File2.cpp ... FileN.cpp
 
-The tool can also be used on a single file or multiple files if a build path is
-passed with the ``-p`` flag.
+The tool can be also used with a compile commands database:
 
 .. code-block:: console
 
-  $ clang-doc /path/to/file.cpp -p /path/to/build
+  $ clang-doc --executor=all-TUs compile_commands.json
+
+To select only a subset of files from the database, use the ``--filter`` flag:
+
+.. code-block:: console
+
+  $ clang-doc --executor=all-TUs --filter=File[0-9]+.cpp compile_commands.json
 
 Output
 ======
@@ -50,7 +54,7 @@ The top-level directory is configurable through the ``output`` flag:
 
 .. code-block:: console
 
-  $ clang-doc -output=output/directory/ compile_commands.json
+  $ clang-doc --output=output/directory/ compile_commands.json
 
 Configuration
 =============
@@ -67,6 +71,16 @@ Options
 .. code-block:: console
 
   $ clang-doc --help
+  OVERVIEW: Generates documentation from source code and comments.
+
+  Example usage for files without flags (default):
+
+    $ clang-doc File1.cpp File2.cpp ... FileN.cpp
+
+  Example usage for a project using a compile commands database:
+
+    $ clang-doc --executor=all-TUs compile_commands.json
+
   USAGE: clang-doc [options] <source0> [... <sourceN>]
 
   OPTIONS: