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Improve performance when fetching Decls. #679

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2 changes: 2 additions & 0 deletions sources/ClangSharp.Interop/Extensions/CXCursor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1834,6 +1834,8 @@ public static void DisposeOverriddenCursors(ReadOnlySpan<CXCursor> overridden)

public readonly CXCursor GetDecl(uint index) => clangsharp.Cursor_getDecl(this, index);

public readonly bool GetDecls(CXCursor* cursors, uint count) => clangsharp.Cursor_getDecls(this, cursors, count);

public readonly void GetDefinitionSpellingAndExtent(out string spelling, out uint startLine, out uint startColumn, out uint endLine, out uint endColumn)
{
fixed (uint* pStartLine = &startLine)
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5 changes: 4 additions & 1 deletion sources/ClangSharp.Interop/clangsharp/clangsharp.cs
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Expand Up @@ -6,7 +6,7 @@

namespace ClangSharp.Interop;

public static partial class @clangsharp
public static unsafe partial class @clangsharp
{
[DllImport("libClangSharp", CallingConvention = CallingConvention.Cdecl, EntryPoint = "clangsharp_Cursor_getArgument", ExactSpelling = true)]
public static extern CXCursor Cursor_getArgument(CXCursor C, [NativeTypeName("unsigned int")] uint i);
Expand Down Expand Up @@ -181,6 +181,9 @@ public static partial class @clangsharp
[DllImport("libClangSharp", CallingConvention = CallingConvention.Cdecl, EntryPoint = "clangsharp_Cursor_getDecl", ExactSpelling = true)]
public static extern CXCursor Cursor_getDecl(CXCursor C, [NativeTypeName("unsigned int")] uint i);

[DllImport("libClangSharp", CallingConvention = CallingConvention.Cdecl, EntryPoint = "clangsharp_Cursor_getDecls", ExactSpelling = true)]
public static extern bool Cursor_getDecls(CXCursor C, CXCursor* decls, [NativeTypeName("unsigned int")] uint count);

[DllImport("libClangSharp", CallingConvention = CallingConvention.Cdecl, EntryPoint = "clangsharp_Cursor_getDeclKind", ExactSpelling = true)]
public static extern CX_DeclKind Cursor_getDeclKind(CXCursor C);

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24 changes: 23 additions & 1 deletion sources/ClangSharp/Cursors/Decls/Decl.cs
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Expand Up @@ -35,7 +35,29 @@ private protected Decl(CXCursor handle, CXCursorKind expectedCursorKind, CX_Decl
_attrs = LazyList.Create<Attr>(Handle.NumAttrs, (i) => TranslationUnit.GetOrCreate<Attr>(Handle.GetAttr(unchecked((uint)i))));
_body = new ValueLazy<Stmt?>(() => !Handle.Body.IsNull ? TranslationUnit.GetOrCreate<Stmt>(Handle.Body) : null);
_canonicalDecl = new ValueLazy<Decl>(() => TranslationUnit.GetOrCreate<Decl>(Handle.CanonicalCursor));
_decls = LazyList.Create<Decl>(Handle.NumDecls, (i) => TranslationUnit.GetOrCreate<Decl>(Handle.GetDecl(unchecked((uint)i))));
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@rolfbjarne rolfbjarne Jan 7, 2026

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FWIW counting the decls (i.e. calling Handle.NumDecls) also shows up in the profile, although not nearly as prominent, so I also considered lazy-loading the count of LazyList instead of having to specify it up-front.

_decls = LazyList.Create<Decl>(Handle.NumDecls, (i) => TranslationUnit.GetOrCreate<Decl>(Handle.GetDecl(unchecked((uint)i))), (list) => {
var cursors = new CXCursor[list.Length];
bool success;
unsafe {
fixed (CXCursor* first = cursors) {
success = Handle.GetDecls(first, unchecked((uint)list.Length));
}
}
if (success)
{
for (var i = 0; i < list.Length; i++)
{
list[i] = TranslationUnit.GetOrCreate<Decl>(cursors[i]);
}
}
else
{
for (var i = 0; i < list.Length; i++)
{
list[i] = TranslationUnit.GetOrCreate<Decl>(Handle.GetDecl(unchecked((uint)i)));
}
}
});
_describedTemplate = new ValueLazy<TemplateDecl?>(() => {
var describedTemplate = Handle.DescribedTemplate;
return describedTemplate.IsNull ? null : TranslationUnit.GetOrCreate<TemplateDecl>(describedTemplate);
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4 changes: 2 additions & 2 deletions sources/ClangSharp/LazyList.cs
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Expand Up @@ -7,14 +7,14 @@ namespace ClangSharp;

internal static class LazyList
{
public static LazyList<T> Create<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(int count, Func<int, T> valueFactory)
public static LazyList<T> Create<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] T>(int count, Func<int, T> valueFactory, Action<T[]>? allValuesFactory = null)
where T : class
{
if (count <= 0)
{
return LazyList<T>.Empty;
}
return new LazyList<T>(count, valueFactory);
return new LazyList<T>(count, valueFactory, allValuesFactory);
}

public static LazyList<T, TBase> Create<T, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TBase>(LazyList<TBase> list, int skip = -1, int take = -1)
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34 changes: 15 additions & 19 deletions sources/ClangSharp/LazyList`1.cs
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Expand Up @@ -12,13 +12,15 @@ internal sealed class LazyList<[DynamicallyAccessedMembers(DynamicallyAccessedMe
{
internal readonly T[] _items;
internal readonly Func<int, T> _valueFactory;
internal readonly Action<T[]>? _allValuesFactory;

public static readonly LazyList<T> Empty = new LazyList<T>(0, _ => null!);

public LazyList(int count, Func<int, T> valueFactory)
public LazyList(int count, Func<int, T> valueFactory, Action<T[]>? allValuesFactory = null)
{
_items = (count <= 0) ? [] : new T[count];
_valueFactory = valueFactory;
_allValuesFactory = allValuesFactory;
}

public T this[int index]
Expand All @@ -30,8 +32,16 @@ public T this[int index]

if (item is null)
{
item = _valueFactory(index);
items[index] = item;
if (_allValuesFactory is not null)
{
_allValuesFactory(_items);
item = _items[index];
}
else
{
item = _valueFactory(index);
items[index] = item;
}
}

return item;
Expand All @@ -56,14 +66,7 @@ public void CopyTo(T[] array, int arrayIndex)

for (var i = 0; i < items.Length; i++)
{
var currentItem = items[i];

if (currentItem is null)
{
currentItem = _valueFactory(i);
items[i] = currentItem;
}

var currentItem = this[i];
array[arrayIndex + i] = currentItem;
}
}
Expand All @@ -76,14 +79,7 @@ public int IndexOf(T item)

for (var i = 0; i < items.Length; i++)
{
var currentItem = items[i];

if (currentItem is null)
{
currentItem = _valueFactory(i);
items[i] = currentItem;
}

var currentItem = this[i];
if (EqualityComparer<T>.Default.Equals(currentItem, item))
{
return i;
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22 changes: 22 additions & 0 deletions sources/libClangSharp/ClangSharp.cpp
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Expand Up @@ -943,6 +943,28 @@ CXType clangsharp_Cursor_getDeclaredReturnType(CXCursor C) {
return MakeCXType(QualType(), getCursorTU(C));
}

bool clangsharp_Cursor_getDecls(CXCursor C, CXCursor* decls, unsigned count) {
if (isDeclOrTU(C.kind)) {
const Decl* D = getCursorDecl(C);

if (const DeclContext* DC = dyn_cast<DeclContext>(D)) {
unsigned n = 0;

for (auto decl : DC->decls()) {
if (n == count) {
return false;
}
decls[n] = MakeCXCursor(decl, getCursorTU(C));
n++;
}

return n == count;
}
}

return false;
}

CXCursor clangsharp_Cursor_getDecl(CXCursor C, unsigned i) {
if (isDeclOrTU(C.kind)) {
const Decl* D = getCursorDecl(C);
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2 changes: 2 additions & 0 deletions sources/libClangSharp/ClangSharp.h
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Expand Up @@ -341,6 +341,8 @@ CLANGSHARP_LINKAGE CXType clangsharp_Cursor_getDeclaredReturnType(CXCursor C);

CLANGSHARP_LINKAGE CXCursor clangsharp_Cursor_getDecl(CXCursor C, unsigned i);

CLANGSHARP_LINKAGE bool clangsharp_Cursor_getDecls(CXCursor C, CXCursor* decls, unsigned count);

CLANGSHARP_LINKAGE CX_DeclKind clangsharp_Cursor_getDeclKind(CXCursor C);

CLANGSHARP_LINKAGE CXCursor clangsharp_Cursor_getDecomposedDecl(CXCursor C);
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1 change: 1 addition & 0 deletions tests/ClangSharp.UnitTests/CXCursor.cs
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Expand Up @@ -10,6 +10,7 @@ public class CXCursorTest : TranslationUnitTest
[Test]
public void AttrKindSpelling()
{
AssertNeedNewClangSharp();
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@rolfbjarne rolfbjarne Jan 7, 2026

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The new native libClangSharp method makes a lot of tests fail because the new code is in a rather fundamental part of ClangSharp, not sure how to handle this?

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@tannergooding tannergooding Jan 9, 2026

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The simplest thing would be to use NativeLibrary.GetExport to try and resolve the new GetDecls API and fallback to the old logic if not present.

I can then fix that up to directly use the new API when I get the new libClangSharp published.


var inputContents =
$$"""
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8 changes: 8 additions & 0 deletions tests/ClangSharp.UnitTests/CursorTests/DeclTest.cs
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Expand Up @@ -15,6 +15,8 @@ public sealed class DeclTest : TranslationUnitTest
[TestCase("public", CX_CXXPublic)]
public void AccessSpecDeclTest(string accessSpecifier, CX_CXXAccessSpecifier expectedAccessSpecifier)
{
AssertNeedNewClangSharp();

var inputContents = $@"struct MyStruct
{{
{accessSpecifier}:
Expand All @@ -32,6 +34,8 @@ public void AccessSpecDeclTest(string accessSpecifier, CX_CXXAccessSpecifier exp
[Test]
public void ClassTemplateDeclTest()
{
AssertNeedNewClangSharp();

var inputContents = $@"template<class T>
class MyClass
{{
Expand All @@ -51,6 +55,8 @@ class MyClass
[Test]
public void ClassTemplatePartialSpecializationDeclTest()
{
AssertNeedNewClangSharp();

var inputContents = $@"template<class T, class U>
class MyClass
{{
Expand Down Expand Up @@ -78,6 +84,8 @@ class MyClass<int, U>
[Test]
public void TemplateParameterPackTest()
{
AssertNeedNewClangSharp();

var inputContents = $@"template<class... Types>
class tuple;

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