[clangd] Add designator hints for parenthesis aggregate initialization #170642

MythreyaK · 2025-12-04T11:06:09Z

Enabled hints for CXXParenListInitExpr,

struct Point {
  int x;
  int y;
};

int main() {
  Point p1{1, 2};  // brace syntax  <-- already present
  Point p2(1, 2);  // parens syntax <-- added in this commit
}

Fixes clangd/clangd#2540

clang-tools-extra/clangd/InlayHints.cpp

zwuis

Could you please add tests with classes having base classes? Aggregates are allowed to have base classes since C++17.

https://en.cppreference.com/w/cpp/language/aggregate_initialization.html

clang-tools-extra/clangd/InlayHints.cpp

MythreyaK · 2025-12-06T07:42:48Z

clang-tools-extra/clangd/unittests/InlayHintTests.cpp

+    struct S1 {
+      int a;
+      int b;
+    };
+
+    struct S2 : S1 { 
+      int c;
+      int d; 
+    };
+    S2 s2 ({$a[[0]], $b[[0]]}, $c[[0]], $d[[0]]);
+  )cpp",
+                        // ExpectedHint{"S1:", "S1"},


Should we add some form of hint here?

S2 s2 ({0, 0}, 0, 0); // S2 s2 ({.a=0, .b=0}, .c=0, .d=0); // current S2 s2 ({0, 0}, 0, 0); // S2 s2 (S1:{.a=0, .b=0}, .c=0, .d=0); // Some hint here? -------------^

@HighCommander4 suggested we add this in a separate PR so that it's easy to revert if that hint is not well received. Will create a separate PR for it.

MythreyaK · 2025-12-06T10:07:29Z

I think I'm seeing a bug. For this snippet,

template <typename T>
struct S1 {
  int a;
  int b;
  T* ptr;
};

struct S2 : S1<S2> {
  int c;
  int d;
  S1<S1> mem;
};
S2 s2 ({0, 0}, 0, 0);
S2 s2 ({$a[[0]], $b[[0]]}, $c[[0]], $d[[0]]);

source range for mem is

------- FieldDecl 1 -------
FIELD: : RecordFields ----- (/llvm-project/clang-tools-extra/clangd/InlayHints.cpp:746)
FieldDecl 0x2233ae10 </clangd-test/TestTU.cpp:10:3, col:7> col:7 c 'int'
--- InitExpr 1 source range ---
 </clangd-test/TestTU.cpp:14:16>
/clangd-test/TestTU.cpp:14:16
/clangd-test/TestTU.cpp:14:16
------------ END ------------

------- FieldDecl 2 -------------------------
FIELD: : RecordFields ----- (/llvm-project/clang-tools-extra/clangd/InlayHints.cpp:746)
FieldDecl 0x2233ae80 </clangd-test/TestTU.cpp:11:3, col:7> col:7 d 'int'
--- InitExpr 2 source range ---
 </clangd-test/TestTU.cpp:14:19>
/clangd-test/TestTU.cpp:14:19
/clangd-test/TestTU.cpp:14:19
------------ END ------------

------- FieldDecl 3 -------------------------
FIELD: : RecordFields ----- (/llvm-project/clang-tools-extra/clangd/InlayHints.cpp:746)
FieldDecl 0x223aaff8 </clangd-test/TestTU.cpp:12:3, col:10> col:10 mem 'S1<S1<S2>>'
--- InitExpr 3 source range ---
 </clangd-test/TestTU.cpp:14:4>
/clangd-test/TestTU.cpp:14:4    // <------ source range seems incorrect?
/clangd-test/TestTU.cpp:14:4    // <------ source range seems incorrect?
------------ END ------------

zwuis · 2025-12-06T11:11:36Z

I'm not sure if it is a bug. But it doesn't block this PR because no need to emit designator hints for mem AFAICT.

Update: Oh I see. We need to distinguish between these cases:

struct S1 {};
struct S2 : S1 {
  int a;
  S1 s1;
};
struct S3 { S3() {} };
struct S4 : S3 {
  int a;
  S3 s3;
};
S2 s2({}, 0);
S4 s4({}, 0, {});

zwuis · 2025-12-06T16:31:52Z

We can use CXXParenListInitExpr::getUserSpecifiedInitExprs() so that we don't need to handle implicit initializations.

MythreyaK · 2025-12-07T08:14:20Z

We can use CXXParenListInitExpr::getUserSpecifiedInitExprs() so that we don't need to handle implicit initializations.

Didn't notice that; Thank you, that fixed it!

llvmbot · 2025-12-07T08:26:00Z

@llvm/pr-subscribers-clang-tools-extra

Author: Mythreya Kuricheti (MythreyaK)

Changes

Enabled hints for CXXParenListInitExpr,

struct Point {
  int x;
  int y;
};

int main() {
  Point p1{1, 2};  // brace syntax  &lt;-- already present
  Point p2(1, 2);  // parens syntax &lt;-- added in this commit
}

Fixes clangd/clangd#2540

Full diff: https://github.com/llvm/llvm-project/pull/170642.diff

2 Files Affected:

(modified) clang-tools-extra/clangd/InlayHints.cpp (+27)
(modified) clang-tools-extra/clangd/unittests/InlayHintTests.cpp (+70-14)

diff --git a/clang-tools-extra/clangd/InlayHints.cpp b/clang-tools-extra/clangd/InlayHints.cpp
index 23bd02304a4fd..040015cfc2d13 100644
--- a/clang-tools-extra/clangd/InlayHints.cpp
+++ b/clang-tools-extra/clangd/InlayHints.cpp
@@ -699,6 +699,33 @@ class InlayHintVisitor : public RecursiveASTVisitor<InlayHintVisitor> {
     return InstantiatedFunction->getParamDecl(ParamIdx);
   }
 
+  bool VisitCXXParenListInitExpr(CXXParenListInitExpr *E) {
+    if (!Cfg.InlayHints.Designators)
+      return true;
+
+    if (const auto *CXXRecord = E->getType()->getAsCXXRecordDecl()) {
+      const auto &InitExprs = E->getUserSpecifiedInitExprs();
+      size_t InitInx = 0;
+
+      // Inherited members are first, skip them for now.
+      // FIXME: '.base=' or 'base:' hint?
+      for (const auto &_ : CXXRecord->bases()) {
+        InitInx++;
+      }
+
+      // Then the members defined in this record
+      auto RecordFields = CXXRecord->fields().begin();
+
+      for (; InitInx < InitExprs.size();
+           ++InitInx, RecordFields = std::next(RecordFields)) {
+        addDesignatorHint(InitExprs[InitInx]->getSourceRange(),
+                          "." + RecordFields->getName().str());
+      }
+    }
+
+    return true;
+  }
+
   bool VisitInitListExpr(InitListExpr *Syn) {
     // We receive the syntactic form here (shouldVisitImplicitCode() is false).
     // This is the one we will ultimately attach designators to.
diff --git a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
index feb4404b3d2bf..d54e36c2f8a3b 100644
--- a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
+++ b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
@@ -1147,20 +1147,6 @@ TEST(ParameterHints, CopyOrMoveConstructor) {
   )cpp");
 }
 
-TEST(ParameterHints, AggregateInit) {
-  // FIXME: This is not implemented yet, but it would be a natural
-  // extension to show member names as hints here.
-  assertParameterHints(R"cpp(
-    struct Point {
-      int x;
-      int y;
-    };
-    void bar() {
-      Point p{41, 42};
-    }
-  )cpp");
-}
-
 TEST(ParameterHints, UserDefinedLiteral) {
   // Do not hint call to user-defined literal operator.
   assertParameterHints(R"cpp(
@@ -1746,6 +1732,19 @@ TEST(TypeHints, SubstTemplateParameterAliases) {
 }
 
 TEST(DesignatorHints, Basic) {
+  assertDesignatorHints(R"cpp(
+    struct Point {
+      int x;
+      int y;
+    };
+    void bar() {
+      Point p{$x[[41]], $y[[42]]};
+    }
+  )cpp",
+                        ExpectedHint{".x=", "x"}, ExpectedHint{".y=", "y"});
+}
+
+TEST(DesignatorHints, BasicArray) {
   assertDesignatorHints(R"cpp(
     struct S { int x, y, z; };
     S s {$x[[1]], $y[[2+2]]};
@@ -1822,6 +1821,63 @@ TEST(DesignatorHints, NoCrash) {
                         ExpectedHint{".b=", "b"});
 }
 
+TEST(DesignatorHints, BasicParenInit) {
+  assertDesignatorHints(R"cpp(
+    struct S { 
+      int x;
+      int y;
+      int z; 
+    };
+    S s ($x[[1]], $y[[2+2]], $z[[4]]);
+  )cpp",
+                        ExpectedHint{".x=", "x"}, ExpectedHint{".y=", "y"},
+                        ExpectedHint{".z=", "z"});
+}
+
+TEST(DesignatorHints, BasicParenInitDerived) {
+  assertDesignatorHints(R"cpp(
+    struct S1 {
+      int a;
+      int b;
+    };
+
+    struct S2 : S1 { 
+      int c;
+      int d; 
+    };
+    S2 s2 ({$a[[0]], $b[[0]]}, $c[[0]], $d[[0]]);
+  )cpp",
+                        // ExpectedHint{"S1:", "S1"},
+                        ExpectedHint{".a=", "a"}, ExpectedHint{".b=", "b"},
+                        ExpectedHint{".c=", "c"}, ExpectedHint{".d=", "d"});
+}
+
+TEST(DesignatorHints, BasicParenInitTemplate) {
+  assertDesignatorHints(R"cpp(
+    template <typename T>
+    struct S1 {
+      int a;
+      int b;
+      T* ptr;
+    };
+
+    struct S2 : S1<S2> {
+      int c;
+      int d;
+      S1<int> mem;
+    };
+
+    int main() {
+      S2 sa ({$a1[[0]], $b1[[0]]}, $c[[0]], $d[[0]], $mem[[S1<int>($a2[[1]], $b2[[2]], $ptr[[nullptr]])]]);
+    }
+  )cpp",
+                        ExpectedHint{".a=", "a1"}, ExpectedHint{".b=", "b1"},
+                        ExpectedHint{".c=", "c"}, ExpectedHint{".d=", "d"},
+                        ExpectedHint{".mem=", "mem"}, ExpectedHint{".a=", "a2"},
+                        ExpectedHint{".b=", "b2"},
+                        ExpectedHint{".ptr=", "ptr"});
+}
+
 TEST(InlayHints, RestrictRange) {
   Annotations Code(R"cpp(
     auto a = false;

llvmbot · 2025-12-07T08:26:00Z

@llvm/pr-subscribers-clangd

Author: Mythreya Kuricheti (MythreyaK)

Changes

Enabled hints for CXXParenListInitExpr,

struct Point {
  int x;
  int y;
};

int main() {
  Point p1{1, 2};  // brace syntax  &lt;-- already present
  Point p2(1, 2);  // parens syntax &lt;-- added in this commit
}

Fixes clangd/clangd#2540

Full diff: https://github.com/llvm/llvm-project/pull/170642.diff

2 Files Affected:

(modified) clang-tools-extra/clangd/InlayHints.cpp (+27)
(modified) clang-tools-extra/clangd/unittests/InlayHintTests.cpp (+70-14)

diff --git a/clang-tools-extra/clangd/InlayHints.cpp b/clang-tools-extra/clangd/InlayHints.cpp
index 23bd02304a4fd..040015cfc2d13 100644
--- a/clang-tools-extra/clangd/InlayHints.cpp
+++ b/clang-tools-extra/clangd/InlayHints.cpp
@@ -699,6 +699,33 @@ class InlayHintVisitor : public RecursiveASTVisitor<InlayHintVisitor> {
     return InstantiatedFunction->getParamDecl(ParamIdx);
   }
 
+  bool VisitCXXParenListInitExpr(CXXParenListInitExpr *E) {
+    if (!Cfg.InlayHints.Designators)
+      return true;
+
+    if (const auto *CXXRecord = E->getType()->getAsCXXRecordDecl()) {
+      const auto &InitExprs = E->getUserSpecifiedInitExprs();
+      size_t InitInx = 0;
+
+      // Inherited members are first, skip them for now.
+      // FIXME: '.base=' or 'base:' hint?
+      for (const auto &_ : CXXRecord->bases()) {
+        InitInx++;
+      }
+
+      // Then the members defined in this record
+      auto RecordFields = CXXRecord->fields().begin();
+
+      for (; InitInx < InitExprs.size();
+           ++InitInx, RecordFields = std::next(RecordFields)) {
+        addDesignatorHint(InitExprs[InitInx]->getSourceRange(),
+                          "." + RecordFields->getName().str());
+      }
+    }
+
+    return true;
+  }
+
   bool VisitInitListExpr(InitListExpr *Syn) {
     // We receive the syntactic form here (shouldVisitImplicitCode() is false).
     // This is the one we will ultimately attach designators to.
diff --git a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
index feb4404b3d2bf..d54e36c2f8a3b 100644
--- a/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
+++ b/clang-tools-extra/clangd/unittests/InlayHintTests.cpp
@@ -1147,20 +1147,6 @@ TEST(ParameterHints, CopyOrMoveConstructor) {
   )cpp");
 }
 
-TEST(ParameterHints, AggregateInit) {
-  // FIXME: This is not implemented yet, but it would be a natural
-  // extension to show member names as hints here.
-  assertParameterHints(R"cpp(
-    struct Point {
-      int x;
-      int y;
-    };
-    void bar() {
-      Point p{41, 42};
-    }
-  )cpp");
-}
-
 TEST(ParameterHints, UserDefinedLiteral) {
   // Do not hint call to user-defined literal operator.
   assertParameterHints(R"cpp(
@@ -1746,6 +1732,19 @@ TEST(TypeHints, SubstTemplateParameterAliases) {
 }
 
 TEST(DesignatorHints, Basic) {
+  assertDesignatorHints(R"cpp(
+    struct Point {
+      int x;
+      int y;
+    };
+    void bar() {
+      Point p{$x[[41]], $y[[42]]};
+    }
+  )cpp",
+                        ExpectedHint{".x=", "x"}, ExpectedHint{".y=", "y"});
+}
+
+TEST(DesignatorHints, BasicArray) {
   assertDesignatorHints(R"cpp(
     struct S { int x, y, z; };
     S s {$x[[1]], $y[[2+2]]};
@@ -1822,6 +1821,63 @@ TEST(DesignatorHints, NoCrash) {
                         ExpectedHint{".b=", "b"});
 }
 
+TEST(DesignatorHints, BasicParenInit) {
+  assertDesignatorHints(R"cpp(
+    struct S { 
+      int x;
+      int y;
+      int z; 
+    };
+    S s ($x[[1]], $y[[2+2]], $z[[4]]);
+  )cpp",
+                        ExpectedHint{".x=", "x"}, ExpectedHint{".y=", "y"},
+                        ExpectedHint{".z=", "z"});
+}
+
+TEST(DesignatorHints, BasicParenInitDerived) {
+  assertDesignatorHints(R"cpp(
+    struct S1 {
+      int a;
+      int b;
+    };
+
+    struct S2 : S1 { 
+      int c;
+      int d; 
+    };
+    S2 s2 ({$a[[0]], $b[[0]]}, $c[[0]], $d[[0]]);
+  )cpp",
+                        // ExpectedHint{"S1:", "S1"},
+                        ExpectedHint{".a=", "a"}, ExpectedHint{".b=", "b"},
+                        ExpectedHint{".c=", "c"}, ExpectedHint{".d=", "d"});
+}
+
+TEST(DesignatorHints, BasicParenInitTemplate) {
+  assertDesignatorHints(R"cpp(
+    template <typename T>
+    struct S1 {
+      int a;
+      int b;
+      T* ptr;
+    };
+
+    struct S2 : S1<S2> {
+      int c;
+      int d;
+      S1<int> mem;
+    };
+
+    int main() {
+      S2 sa ({$a1[[0]], $b1[[0]]}, $c[[0]], $d[[0]], $mem[[S1<int>($a2[[1]], $b2[[2]], $ptr[[nullptr]])]]);
+    }
+  )cpp",
+                        ExpectedHint{".a=", "a1"}, ExpectedHint{".b=", "b1"},
+                        ExpectedHint{".c=", "c"}, ExpectedHint{".d=", "d"},
+                        ExpectedHint{".mem=", "mem"}, ExpectedHint{".a=", "a2"},
+                        ExpectedHint{".b=", "b2"},
+                        ExpectedHint{".ptr=", "ptr"});
+}
+
 TEST(InlayHints, RestrictRange) {
   Annotations Code(R"cpp(
     auto a = false;

Co-authored-by: zwuis <zwuis@outlook.com>

MythreyaK added 2 commits December 3, 2025 21:41

Enable designator hints test

64e2e83

[clangd] Add designator hints for parenthesis aggregate initialization

50042b1

MythreyaK commented Dec 4, 2025

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zwuis reviewed Dec 4, 2025

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MythreyaK commented Dec 6, 2025

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MythreyaK marked this pull request as ready for review December 7, 2025 08:25

llvmbot added clang-tools-extra clangd labels Dec 7, 2025

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Co-authored-by: zwuis <zwuis@outlook.com>

MythreyaK requested a review from zwuis December 7, 2025 11:38

zwuis requested a review from HighCommander4 December 7, 2025 13:52

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[clangd] Add designator hints for parenthesis aggregate initialization #170642

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