Fix the same $ procedure argument generating duplicate instantiations

src/checker.cpp

@@ -2153,7 +2153,9 @@ gb_internal void add_entity_use(CheckerContext *c, Ast *identifier, Entity *enti
 	if (identifier == nullptr || identifier->kind != Ast_Ident) {
 		return;
 	}
-	entity->identifier.store(identifier);
+	// NOTE: only set it once, as `$` procedure arguments are matched by this identifier
+	Ast *empty_ident = nullptr;
+	entity->identifier.compare_exchange_strong(empty_ident, identifier);
 
 	identifier->Ident.entity = entity;
 

tests/issues/run.bat

@@ -46,6 +46,7 @@ set COMMON=-define:ODIN_TEST_FANCY=false -file -vet -strict-style -ignore-unused
 ..\..\..\odin test ..\test_issue_bool_comparison_truthiness.odin %COMMON%  || exit /b
 ..\..\..\odin test ..\test_issue_const_array_broadcast.odin %COMMON%  || exit /b
 ..\..\..\odin test ..\test_issue_forwarded_poly_proc.odin %COMMON%  || exit /b
+..\..\..\odin test ..\test_issue_proc_constant_instantiation.odin %COMMON%  || exit /b
 ..\..\..\odin check ..\test_issue_7336.odin -no-entry-point %COMMON% || exit /b
 ..\..\..\odin check ..\test_issue_ellipsis_type_call.odin -no-entry-point %COMMON% 2>&1 | find /c "Error:" | findstr /x "10" || exit /b
 ..\..\..\odin check ..\test_issue_foreign_redeclaration.odin -no-entry-point %COMMON% || exit /b

tests/issues/run.sh

@@ -109,6 +109,7 @@ $ODIN test ../test_issue_bool_to_be_conversion.odin $COMMON
 $ODIN test ../test_issue_bool_comparison_truthiness.odin $COMMON
 $ODIN test ../test_issue_const_array_broadcast.odin $COMMON
 $ODIN test ../test_issue_forwarded_poly_proc.odin $COMMON
+$ODIN test ../test_issue_proc_constant_instantiation.odin $COMMON
 $ODIN test ../test_issue_swizzle_multi_assign.odin $COMMON
 
 $ODIN check ../test_issue_foreign_redeclaration.odin -no-entry-point $COMMON_CHECK

tests/issues/test_issue_proc_constant_instantiation.odin

@@ -0,0 +1,17 @@
+package test_issues
+
+import "core:testing"
+
+// Passing the same procedure to a `$` parameter from two calls used to generate two instantiations,
+// each with its own `Box` crashing the compiler.
+
+box_of :: proc($f: proc() -> int) -> typeid {
+	Box :: struct {}
+	return Box
+}
+one :: proc() -> int { return 1 }
+
+@(test)
+proc_constant_instantiation :: proc(t: ^testing.T) {
+	testing.expect_value(t, box_of(one), box_of(one))
+}