[PATCH] D103789: [clangd] Type hints for C++14 return type deduction

[Nathan Ridge via Phabricator via cfe-commits]

nridge created this revision.
nridge added a reviewer: sammccall.
Herald added subscribers: usaxena95, kadircet, arphaman.
nridge requested review of this revision.
Herald added subscribers: cfe-commits, MaskRay, ilya-biryukov.
Herald added a project: clang-tools-extra.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103789

Files:
  clang-tools-extra/clangd/InlayHints.cpp
  clang-tools-extra/clangd/unittests/InlayHintTests.cpp


Index: clang-tools-extra/clangd/unittests/InlayHintTests.cpp
===================================================================
--- clang-tools-extra/clangd/unittests/InlayHintTests.cpp
+++ clang-tools-extra/clangd/unittests/InlayHintTests.cpp
@@ -478,14 +478,32 @@
 }
 
 TEST(TypeHints, ReturnTypeDeduction) {
-  // FIXME: Not handled yet.
-  // This test is currently here mostly because a naive implementation
-  // might have us print something not super helpful like the function type.
-  assertTypeHints(R"cpp(
-    auto func(int x) {
-      return x + 1;
-    }
-  )cpp");
+  assertTypeHints(
+      R"cpp(
+    $ret1a[[auto]] f1(int x);  // Hint forward declaration too
+    $ret1b[[auto]] f1(int x) { return x + 1; }
+
+    // Include pointer operators in both location and hint
+    // (we could also go the other way).
+    int s;
+    $ret2[[auto&]] f2() { return s; }
+
+    // Do not hint `auto` for trailing return type.
+    auto f3() -> int;
+
+    // `auto` conversion operator
+    struct A {
+      operator $retConv[[auto]]() { return 42; }
+    };
+
+    // FIXME: Dependent types do not work yet.
+    template <typename T>
+    struct S {
+      auto method() { return T(); }
+    };
+  )cpp",
+      ExpectedHint{": int", "ret1a"}, ExpectedHint{": int", "ret1b"},
+      ExpectedHint{": int &", "ret2"}, ExpectedHint{": int", "retConv"});
 }
 
 TEST(TypeHints, DependentType) {
Index: clang-tools-extra/clangd/InlayHints.cpp
===================================================================
--- clang-tools-extra/clangd/InlayHints.cpp
+++ clang-tools-extra/clangd/InlayHints.cpp
@@ -72,6 +72,23 @@
     return true;
   }
 
+  bool VisitFunctionDecl(FunctionDecl *D) {
+    if (auto *AT = D->getReturnType()->getContainedAutoType()) {
+      QualType Deduced = AT->getDeducedType();
+      if (!Deduced.isNull()) {
+        SourceRange R = D->getReturnTypeSourceRange();
+        // For operator auto(), have to get location of `auto` a different way.
+        if (R.isInvalid() && isa<CXXConversionDecl>(D)) {
+          R = D->getTypeSourceInfo()->getTypeLoc().getBeginLoc();
+        }
+        addInlayHint(R, InlayHintKind::TypeHint,
+                     ": " + D->getReturnType().getAsString(TypeHintPolicy));
+      }
+    }
+
+    return true;
+  }
+
   bool VisitVarDecl(VarDecl *D) {
     // Do not show hints for the aggregate in a structured binding.
     // In the future, we may show hints for the individual bindings.


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