[clang] [clang] Add FixItHint for designated init order (PR #173136)
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Fri Dec 19 23:51:41 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Mythreya Kuricheti (MythreyaK)
<details>
<summary>Changes</summary>
Generates `FixItHint` for reordering incorrectly initialized designated initializers.
[vid.webm](https://github.com/user-attachments/assets/079ae121-77a8-4ca7-9935-efc7f0a36d19)
>From issue clangd/clangd#<!-- -->965 ([comment](https://github.com/clangd/clangd/issues/965#issuecomment-1001257300))
> What do you think about adding/improving fix actions for misordered initializers instead. Would it help much?
---
Full diff: https://github.com/llvm/llvm-project/pull/173136.diff
3 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+3)
- (modified) clang/lib/Sema/SemaInit.cpp (+65-3)
- (added) clang/test/SemaCXX/cxx20-designated-initializer-fixits.cpp (+105)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 994ac444d4aa1..ba14a50c1f177 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -493,6 +493,9 @@ Improvements to Clang's diagnostics
carries messages like 'In file included from ...' or 'In module ...'.
Now the include/import locations are written into `sarif.run.result.relatedLocations`.
+- Clang now generates a fix-it for C++20 designated initializers when the
+ initializers do not match the declaration order in the structure.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index cc6ddf568d346..6decf0d809153 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -31,8 +31,10 @@
#include "clang/Sema/SemaHLSL.h"
#include "clang/Sema/SemaObjC.h"
#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/ErrorHandling.h"
@@ -3092,6 +3094,65 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
PrevField = *FI;
}
+ const auto GenerateDesignatedInitReorderingFixit =
+ [&](SemaBase::SemaDiagnosticBuilder &Diags) {
+ struct ReorderInfo {
+ int Pos{};
+ const Expr *InitExpr{};
+ };
+
+ llvm::SmallDenseMap<IdentifierInfo *, int> MemberNameInx{};
+ llvm::SmallVector<ReorderInfo, 16> ReorderedInitExprs{};
+
+ const auto *CxxRecord =
+ IList->getSemanticForm()->getType()->getAsCXXRecordDecl();
+
+ for (const auto &Field : CxxRecord->fields()) {
+ MemberNameInx[Field->getIdentifier()] = Field->getFieldIndex();
+ }
+
+ for (const auto *Init : IList->inits()) {
+ if (const auto *DI =
+ dyn_cast_if_present<DesignatedInitExpr>(Init)) {
+ // We expect only one Designator
+ if (DI->size() != 1)
+ return;
+
+ const auto *const FieldName =
+ DI->getDesignator(0)->getFieldName();
+ // In case we have an unknown initializer in the source, not in
+ // the record
+ if (MemberNameInx.contains(FieldName))
+ ReorderedInitExprs.emplace_back(
+ ReorderInfo{MemberNameInx.at(FieldName), Init});
+ }
+ }
+
+ llvm::sort(ReorderedInitExprs, [](const auto &A, const auto &B) {
+ return A.Pos < B.Pos;
+ });
+
+ llvm::SmallString<128> FixedInitList{};
+ SourceManager &SM = SemaRef.getSourceManager();
+ const LangOptions &LangOpts = SemaRef.getLangOpts();
+
+ // In a derived Record, first n base-classes are initialized first.
+ // They do not use designated init, so skip them
+ const auto IListInits =
+ IList->inits().drop_front(CxxRecord->getNumBases());
+ // loop over each existing expressions and apply replacement
+ for (const auto &[OrigExpr, Repl] :
+ llvm::zip(IListInits, ReorderedInitExprs)) {
+ CharSourceRange CharRange = CharSourceRange::getTokenRange(
+ Repl.InitExpr->getSourceRange());
+ const auto InitText =
+ Lexer::getSourceText(CharRange, SM, LangOpts);
+
+ Diags << FixItHint::CreateReplacement(OrigExpr->getSourceRange(),
+ InitText.str());
+ }
+ };
+
if (PrevField &&
PrevField->getFieldIndex() > KnownField->getFieldIndex()) {
SemaRef.Diag(DIE->getInit()->getBeginLoc(),
@@ -3101,9 +3162,10 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
unsigned OldIndex = StructuredIndex - 1;
if (StructuredList && OldIndex <= StructuredList->getNumInits()) {
if (Expr *PrevInit = StructuredList->getInit(OldIndex)) {
- SemaRef.Diag(PrevInit->getBeginLoc(),
- diag::note_previous_field_init)
- << PrevField << PrevInit->getSourceRange();
+ auto Diags = SemaRef.Diag(PrevInit->getBeginLoc(),
+ diag::note_previous_field_init)
+ << PrevField << PrevInit->getSourceRange();
+ GenerateDesignatedInitReorderingFixit(Diags);
}
}
}
diff --git a/clang/test/SemaCXX/cxx20-designated-initializer-fixits.cpp b/clang/test/SemaCXX/cxx20-designated-initializer-fixits.cpp
new file mode 100644
index 0000000000000..7dfdd62df292f
--- /dev/null
+++ b/clang/test/SemaCXX/cxx20-designated-initializer-fixits.cpp
@@ -0,0 +1,105 @@
+// RUN: %clang_cc1 -std=c++20 %s -Wreorder-init-list -fdiagnostics-parseable-fixits 2>&1 | FileCheck %s
+
+// These tests are from clang/test/SemaCXX/cxx2a-initializer-aggregates.cpp
+struct C { int :0, x, :0, y, :0; };
+C c = {
+ .x = 1,
+ .x = 1,
+ .y = 1,
+ .y = 1,
+ .x = 1,
+ .x = 1,
+};
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".x = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".x = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".x = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".x = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".y = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:3-[[@LINE-7]]:9}:".y = 1"
+
+namespace GH63605 {
+struct A {
+ unsigned x;
+ unsigned y;
+ unsigned z;
+};
+
+struct B {
+ unsigned a;
+ unsigned b;
+};
+
+struct : public A, public B {
+ unsigned : 2;
+ unsigned a : 6;
+ unsigned : 1;
+ unsigned b : 6;
+ unsigned : 2;
+ unsigned c : 6;
+ unsigned d : 1;
+ unsigned e : 2;
+} data = {
+ {.z=0,
+
+
+ .y=1,
+
+ .x=2},
+ {.b=3,
+ .a=4},
+ .e = 1,
+
+ .d = 1,
+
+ .c = 1,
+ .b = 1,
+ .a = 1,
+};
+}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-17]]:4-[[@LINE-17]]:8}:".x=2"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-15]]:4-[[@LINE-15]]:8}:".y=1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-14]]:4-[[@LINE-14]]:8}:".z=0"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-14]]:4-[[@LINE-14]]:8}:".a=4"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-14]]:4-[[@LINE-14]]:8}:".b=3"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-14]]:5-[[@LINE-14]]:11}:".a = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-13]]:5-[[@LINE-13]]:11}:".b = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-12]]:5-[[@LINE-12]]:11}:".c = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-12]]:5-[[@LINE-12]]:11}:".d = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-12]]:5-[[@LINE-12]]:11}:".e = 1"
+// END tests from clang/test/SemaCXX/cxx2a-initializer-aggregates.cpp
+
+namespace reorder_derived {
+struct col {
+ int r;
+ int g;
+ int b;
+};
+
+struct point {
+ float x;
+ float y;
+ float z;
+};
+
+struct derived : public col, public point {
+ int z2;
+ int z1;
+};
+
+void test() {
+ derived a {
+ {.b = 1, .g = 2, .r = 3},
+ { .z = 1, .y=2, .x = 3 },
+ .z1 = 1,
+ .z2 = 2,
+ };
+}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-6]]:6-[[@LINE-6]]:12}:".r = 3"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:14-[[@LINE-7]]:20}:".g = 2"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-8]]:22-[[@LINE-8]]:28}:".b = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-8]]:15-[[@LINE-8]]:19}:".y=2"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-9]]:21-[[@LINE-9]]:28}:".z = 1"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-10]]:7-[[@LINE-10]]:13}:".x = 3"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-10]]:5-[[@LINE-10]]:12}:".z2 = 2"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-10]]:5-[[@LINE-10]]:12}:".z1 = 1"
+} // namespace reorder_derived
``````````
</details>
https://github.com/llvm/llvm-project/pull/173136
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