[clang-repl] add %help, documentation, and tests for %commands

clang/docs/ClangRepl.rst

@@ -159,8 +159,21 @@ Lamdas:
    clang-repl> welcome();
    Welcome to REPL
 
-Using Dynamic Library:
-======================
+Built in Commands:
+==================
+clang-repl has some special commands that are of the form `%<something>`. To list all these commands, use the `%help` command:
+
+Help:
+=====
+The `%help` command lists all built in clang-repl commands.
+
+.. code-block:: text
+
+   clang-repl> %help
+
+Using Dynamic Libraries:
+========================
+The `%lib` command links a dynamic library.
 
 .. code-block:: text
 
@@ -189,21 +202,40 @@ Using Dynamic Library:
    clang++-17  -c -o print.o print.cpp
    clang-17 -shared print.o -o print.so
 
-Comments:
-=========
+Undo:
+=====
+The `%undo` command reverts the previous input.
 
 .. code-block:: text
 
-   clang-repl> // Comments in Clang-Repl
-   clang-repl> /* Comments in Clang-Repl */
+   clang-repl> int a = 1; a
+   (int) 1
+   clang-repl> %undo
+   clang-repl> a
+   In file included from <<< inputs >>>:1:
+   input_line_2:1:1: error: use of undeclared identifier 'a'
+   1 | a
+   * | ^
+   error: Parsing failed.
 
 
-Closure or Termination:
+Quit:
 =======================
+The `%quit` command terminates clang-repl.
 
 .. code-block:: text
 
-   clang-repl>%quit
+   clang-repl> %quit
+
+Comments:
+=========
+
+.. code-block:: text
+
+   clang-repl> // Comments in Clang-Repl
+   clang-repl> /* Comments in Clang-Repl */
+
+
 
 
 Just like Clang, Clang-Repl can be integrated in existing applications as a library

clang/tools/clang-repl/ClangRepl.cpp

@@ -185,7 +185,7 @@ struct ReplListCompleter {
   clang::Interpreter &MainInterp;
   ReplListCompleter(clang::IncrementalCompilerBuilder &CB,
                     clang::Interpreter &Interp)
-      : CB(CB), MainInterp(Interp){};
+      : CB(CB), MainInterp(Interp) {};
 
   std::vector<llvm::LineEditor::Completion> operator()(llvm::StringRef Buffer,
                                                        size_t Pos) const;
@@ -347,6 +347,14 @@ int main(int argc, const char **argv) {
     }
   }
 
+  // If we add more % commands, there should be better architecture than this.
+  const char *help_output = "%help\t\tlist clang-repl %commands\n"
+                            "%undo\t\tundo the previous input\n"
+                            "%lib\t<path>\tlink a dynamic library\n"
+                            "%quit\t\texit clang-repl\n";
+
+  const char *lib_bad_args =
+      "%lib expects 1 argument: the path to a dynamic library\n";
   if (OptInputs.empty()) {
     llvm::LineEditor LE("clang-repl");
     std::string Input;
@@ -370,9 +378,24 @@ int main(int argc, const char **argv) {
       if (Input == R"(%undo)") {
         if (auto Err = Interp->Undo())
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
+      } else if (Input == R"(%help)") {
+        auto Err =
+            llvm::make_error<llvm::StringError>(help_output, std::error_code());
+        llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "");
+      } else if (Input == R"(%lib)") {
+        auto Err = llvm::make_error<llvm::StringError>(lib_bad_args,
+                                                       std::error_code());
+        llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
       } else if (Input.rfind("%lib ", 0) == 0) {
         if (auto Err = Interp->LoadDynamicLibrary(Input.data() + 5))
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
+      } else if (Input[0] == '%') { // make sure this is evaluated last
+        auto Err = llvm::make_error<llvm::StringError>(
+            llvm::formatv(
+                "Invalid % command \"{0}\", use \"%help\" to list commands\n",
+                Input),
+            std::error_code());
+        llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
       } else if (auto Err = Interp->ParseAndExecute(Input)) {
         llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
       }