[clangd] Place cursor better after completing patterns

Summary:
By producing the $0 marker in the snippets at the last placeholder.
This produces nicer results in most cases, e.g. for
   namespace <#name#> {
     <#decls#>
   }

we now produce ${0:decls} instead of ${2:decls} and the final cursor
placement is more convenient.

Reviewers: hokein

Reviewed By: hokein

Subscribers: MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62389

llvm-svn: 361841

1 files changed, 23 insertions, 4 deletions

diff --git a/clang-tools-extra/clangd/CodeCompletionStrings.cpp b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
index 586be67e92c..bf3cabc2698 100644
--- a/clang-tools-extra/clangd/CodeCompletionStrings.cpp
+++ b/clang-tools-extra/clangd/CodeCompletionStrings.cpp
@@ -11,6 +11,8 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/RawCommentList.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Sema/CodeCompleteConsumer.h"
+#include <limits>
 #include <utility>
 
 namespace clang {
@@ -73,8 +75,23 @@ std::string getDeclComment(const ASTContext &Ctx, const NamedDecl &Decl) {
 }
 
 void getSignature(const CodeCompletionString &CCS, std::string *Signature,
-                  std::string *Snippet, std::string *RequiredQualifiers) {
-  unsigned ArgCount = 0;
+                  std::string *Snippet, std::string *RequiredQualifiers,
+                  bool CompletingPattern) {
+  // Placeholder with this index will be ${0:…} to mark final cursor position.
+  // Usually we do not add $0, so the cursor is placed at end of completed text.
+  unsigned CursorSnippetArg = std::numeric_limits<unsigned>::max();
+  if (CompletingPattern) {
+    // In patterns, it's best to place the cursor at the last placeholder, to
+    // handle cases like
+    //    namespace ${1:name} {
+    //      ${0:decls}
+    //    }
+    CursorSnippetArg =
+        llvm::count_if(CCS, [](const CodeCompletionString::Chunk &C) {
+          return C.Kind == CodeCompletionString::CK_Placeholder;
+        });
+  }
+  unsigned SnippetArg = 0;
   bool HadObjCArguments = false;
   for (const auto &Chunk : CCS) {
     // Informative qualifier chunks only clutter completion results, skip
@@ -124,8 +141,10 @@ void getSignature(const CodeCompletionString &CCS, std::string *Signature,
       break;
     case CodeCompletionString::CK_Placeholder:
       *Signature += Chunk.Text;
-      ++ArgCount;
-      *Snippet += "${" + std::to_string(ArgCount) + ':';
+      ++SnippetArg;
+      *Snippet +=
+          "${" +
+          std::to_string(SnippetArg == CursorSnippetArg ? 0 : SnippetArg) + ':';
       appendEscapeSnippet(Chunk.Text, Snippet);
       *Snippet += '}';
       break;