[clang-repl] Enable basic multiline support.

[v.g.vassilev]

Summary

This patch allows the users to use backslash to tell clang-repl that more input is coming. This would help support OpenMP directives which generally require to be in separate lines.

[aaron.ballman]

clang/test/Interpreter/multiline.cpp

12–17

Another fun test case:

// Requires -ftrigraphs but the following line ends with a backslash (surprise!)
i=??/
  12;

[v.g.vassilev]

clang/test/Interpreter/multiline.cpp

12–17

Yes, the implementation of the multiline support here is actually rather rudimentary. It intentionally does not include deeper language understanding but provides a way for the users typing "well-behaved" code to tell clang-repl that more is coming before it could compile it. In theory we could check for the ??/ trigraph and do the same but I don't think that would be used people use clang-repl on things like IBM 3270 terminals which seem not to have some characters and trigraphs could help there ;)

Our full-fledged solution is described here https://discourse.llvm.org/t/rfc-flexible-lexer-buffering-for-handling-incomplete-input-in-interactive-c-c/64180/9

Until that lands we can have this to unblock work on things like OpenMP support.

[aaron.ballman]

LGTM!

clang/test/Interpreter/multiline.cpp

12–17

Okay, that's reasonable enough for the initial commit. Thanks!

[v.g.vassilev]

Landed in c96c5edb58ed29e0fd936bc082ec6cae7082854e

clang/test/Interpreter/multiline.cpp

+// REQUIRES: host-supports-jit
+// UNSUPPORTED: system-aix
+// RUN: cat %s | clang-repl | FileCheck %s
+
+extern "C" int printf(const char*,...);
+int i = \
+  12;
+
+printf("i=%d\n", i);
+// CHECK: i=12
+
+void f(int x) \ 
+{                                               \
+  printf("x=\
+          %d", x); \
+}
+f(i);
+// CHECK: x=12
+
+// FIXME: Support preprocessor directives.
+// #if 0 \
+//   #error "Can't be!" \
+// #endif
+

clang/tools/clang-repl/ClangRepl.cpp

if (auto Err = Interp->ParseAndExecute(input))
       llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
   }
 
   bool HasError = false;
 
   if (OptInputs.empty()) {
     llvm::LineEditor LE("clang-repl");
     // FIXME: Add LE.setListCompleter
+    std::string Input;
     while (std::optional<std::string> Line = LE.readLine()) {
-      if (*Line == R"(%quit)")
+      llvm::StringRef L = *Line;
+      L = L.trim();
+      if (L.endswith("\\")) {
+        // FIXME: Support #ifdef X \ ...
+        Input += L.drop_back(1);
+        LE.setPrompt("clang-repl...   ");
+        continue;
+      }
+
+      Input += L;
+
+      if (Input == R"(%quit)") {
         break;
-      if (*Line == R"(%undo)") {
+      } else if (Input == R"(%undo)") {
         if (auto Err = Interp->Undo()) {
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
           HasError = true;
         }
-        continue;
-      }
-      if (Line->rfind("%lib ", 0) == 0) {
-        if (auto Err = Interp->LoadDynamicLibrary(Line->data() + 5)) {
+      } else if (Input.rfind("%lib ", 0) == 0) {
+        if (auto Err = Interp->LoadDynamicLibrary(Input.data() + 5)) {
           llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
           HasError = true;
         }
-        continue;
-      }
-
-      if (auto Err = Interp->ParseAndExecute(*Line)) {
+      } else if (auto Err = Interp->ParseAndExecute(Input)) {
         llvm::logAllUnhandledErrors(std::move(Err), llvm::errs(), "error: ");
         HasError = true;
       }
+
+      Input = "";
+      LE.setPrompt("clang-repl> ");
     }
   }
 
   // Our error handler depends on the Diagnostics object, which we're
   // potentially about to delete. Uninstall the handler now so that any
   // later errors use the default handling behavior instead.
   llvm::remove_fatal_error_handler();
 
   return checkDiagErrors(Interp->getCompilerInstance(), HasError);
 }