Fix cycle removal bugs

src/generator/codegen.jl

@@ -543,7 +543,7 @@ function emit!(dag::ExprDAG, node::ExprNode{StructMutualRef}, options::Dict; arg
 
             if node_idx < field_idx
                 # this assumes that circular references were removed at pointers
-                @assert is_jl_pointer(jlty)
+                @assert is_jl_pointer(jlty) "Expected this field to be a pointer: $(struct_sym).$(field_sym)"
 
                 # also emit the original expressions, so we can add corresponding comments
                 # in the pretty-print pass

src/generator/passes.jl

@@ -361,10 +361,10 @@ function (x::RemoveCircularReference)(dag::ExprDAG, options::Dict)
     count = 0
     while any(x -> x != PERMANENT, marks) && (count += 1) < MAX_CIRCIR_DETECTION_COUNT
         fill!(marks, UNMARKED)
-        for (i, node) in enumerate(dag.nodes)
-            marks[i] == UNMARKED || continue
+        for (node_idx, node) in enumerate(dag.nodes)
+            marks[node_idx] == UNMARKED || continue
             cycle = Int[]
-            detect_cycle!(dag.nodes, marks, cycle, i)
+            detect_cycle!(dag.nodes, marks, cycle, node_idx)
             isempty(cycle) && continue
 
             # firstly remove cycle reference caused by mutually referenced structs
@@ -383,10 +383,14 @@ function (x::RemoveCircularReference)(dag::ExprDAG, options::Dict)
                         dag.nodes[nc] = ExprNode(id, ty, child.cursor, child.exprs, child.adj)
                         show_info &&
                             @info "[RemoveCircularReference]: removed $(child.id)'s dependency $(parent.id)"
+
+                        # Now the cycle is broken and we don't need to look at
+                        # any other nodes in the cycle path.
+                        break
                     end
                 end
                 # exit earlier
-                (i + 1) == first(cycle) && break
+                (node_idx + 1) == first(cycle) && break
             end
 
             # there are cases where the circular reference can only be de-referenced at a
@@ -405,8 +409,9 @@ function (x::RemoveCircularReference)(dag::ExprDAG, options::Dict)
                     dag.nodes[nc] = ExprNode(id, ty, child.cursor, child.exprs, child.adj)
                     show_info &&
                         @info "[RemoveCircularReference]: removed $(child.id)'s dependency $(parent.id)"
+
                     # exit earlier
-                    (i + 1) == first(cycle) && break
+                    break
                 end
             end
 

test/generators.jl

@@ -2,7 +2,7 @@ using Clang
 using Clang.Generators
 using Clang.LibClang.Clang_jll
 using Test
-using Clang.Generators: strip_comment_markers
+using Clang.Generators: StructMutualRef, strip_comment_markers
 
 include("rewriter.jl")
 
@@ -57,6 +57,22 @@ end
     @test include("LibDependency.jl") isa Any
 end
 
+# See:
+# - https://github.com/JuliaInterop/Clang.jl/discussions/440
+# - https://github.com/JuliaInterop/Clang.jl/pull/441
+@testset "Cycle detection" begin
+    args = get_default_args()
+    headers = joinpath(@__DIR__, "include", "cycle-detection.h")
+    ctx = create_context(headers, args)
+    build!(ctx)
+
+    # In this particular case there is only one cycle in B, so only B should be
+    # a StructMutualRef.
+    mutual_ref_nodes = [node for node in ctx.dag.nodes if node.type == StructMutualRef()]
+    @test length(mutual_ref_nodes) == 1
+    @test mutual_ref_nodes[1].id == :B
+end
+
 @testset "Issue 320" begin
     args = get_default_args()
     dir = joinpath(@__DIR__, "sys")

test/include/cycle-detection.h

@@ -0,0 +1,32 @@
+typedef struct A A;
+typedef struct B B;
+typedef struct C C;
+
+struct B;
+struct C;
+
+struct B
+{
+    B* x;
+};
+
+struct C
+{
+    B y[10];
+};
+
+typedef struct vector_C
+{
+    C* c;
+} vector_C;
+
+typedef struct pool_C
+{
+    vector_C vc;
+} pool_C;
+
+struct A
+{
+    pool_C pc;
+    C* c;
+};