Add compile-time support for list.pop (#2659)

* Implement `list.pop` for `ListConstant`

* Support non-constant argument to `list.pop`

* Tests: Add tests and update references

* Be more verbose with handling `nullptr`

Co-authored-by: Shaikh Ubaid <shaikhubaid769@gmail.com>

* Check for no arguments

Co-authored-by: Shaikh Ubaid <shaikhubaid769@gmail.com>

* Simplify compile-time evaluation logic

* Handle modifying attribute on a compile time value

* Tests: Update references

* Tests: Print before asserts

* Delete tests/reference/asr-func_04-eef2656.stdout

---------

Co-authored-by: Shaikh Ubaid <shaikhubaid769@gmail.com>

Author: kmr-srbh

integration_tests/test_list_pop.py

@@ -65,4 +65,32 @@ def test_list_pop():
         j += 1
     assert len(l2) == 0
 
+    # list.pop on list constant
+    print([1, 2, 3, 4, 5].pop())
+    assert [1, 2, 3, 4, 5].pop() == 5
+
+    print([1, 2, 3, 4, 5].pop(3))
+    assert [1, 2, 3, 4, 5].pop(3) == 4
+
+    index: i32 = 1
+    print([1, 2, 3, 4, 5].pop(index))
+    assert [1, 2, 3, 4, 5].pop(index) == 2
+
+    element_1: i32 = [1, 2, 3, 4, 5].pop()
+    print(element_1)
+    assert element_1 == 5
+
+    element_2: i32 = [1, 2, 3, 4, 5].pop(2)
+    print(element_2)
+    assert element_2 == 3
+
+    a: i32 = 5
+    b: i32 = 3
+
+    print([(1, 2), (3, 4), (5, 6)].pop(a//b)) 
+    assert [(1, 2), (3, 4), (5, 6)].pop(a//b) == (3, 4)
+
+    print([["a", "b"], ["c", "d"], ["e", "f"]].pop())
+    assert [["a", "b"], ["c", "d"], ["e", "f"]].pop() == ["e", "f"]
+
 test_list_pop()

src/libasr/pass/intrinsic_functions.h

@@ -4672,9 +4672,24 @@ static inline void verify_args(const ASR::IntrinsicElementalFunction_t& x, diag:
 }
 
 static inline ASR::expr_t *eval_list_pop(Allocator &/*al*/,
-    const Location &/*loc*/, ASR::ttype_t */*t*/, Vec<ASR::expr_t*>& /*args*/, diag::Diagnostics& /*diag*/) {
-    // TODO: To be implemented for ListConstant expression
-    return nullptr;
+    const Location &/*loc*/, ASR::ttype_t */*t*/, Vec<ASR::expr_t*>& args, diag::Diagnostics& /*diag*/) {
+        if (args.n == 0 || args[0] == nullptr) {
+            return nullptr;
+        }
+        ASR::ListConstant_t* clist = ASR::down_cast<ASR::ListConstant_t>(args[0]);
+        int64_t index;
+
+        if (args.n == 1) {
+            index = clist->n_args - 1;
+            return clist->m_args[index];
+        } else {
+            if (args[1] == nullptr) {
+                return nullptr;
+            }
+            index = ASR::down_cast<ASR::IntegerConstant_t>(ASRUtils::expr_value(args[1]))->m_n;
+            return clist->m_args[index];
+        }
+
 }
 
 static inline ASR::asr_t* create_ListPop(Allocator& al, const Location& loc,

src/lpython/semantics/python_ast_to_asr.cpp

@@ -7659,6 +7659,20 @@ we will have to use something else.
                     }
                 }
             }
+        } else if (AST::is_a<AST::List_t>(*at->m_value)) {
+            AST::List_t* clist = AST::down_cast<AST::List_t>(at->m_value);
+            visit_List(*clist);
+            if (tmp == nullptr) {
+                throw SemanticError("cannot call " + std::string(at->m_attr) + " on an empty list" , loc);
+            }
+            ASR::expr_t* list_expr = ASR::down_cast<ASR::expr_t>(tmp);
+            Vec<ASR::expr_t*> eles;
+            eles.reserve(al, args.size());
+            for (size_t i=0; i<args.size(); i++) {
+                eles.push_back(al, args[i].m_value);
+            }
+            handle_builtin_attribute(list_expr, at->m_attr, loc, eles);
+            return;
         } else if (AST::is_a<AST::Dict_t>(*at->m_value)) {
             AST::Dict_t* cdict = AST::down_cast<AST::Dict_t>(at->m_value);
             visit_Dict(*cdict);

src/lpython/semantics/python_attribute_eval.h

@@ -75,10 +75,12 @@ struct AttributeHandler {
         }
         std::string key = class_name + "@" + attr_name;
         if (modify_attr_set.find(key) != modify_attr_set.end()) {
-            ASR::Variable_t* v = ASRUtils::EXPR2VAR(e);
-            if (v->m_intent == ASRUtils::intent_in) {
-                throw SemanticError("Modifying input function parameter `"
-                            + std::string(v->m_name) + "` is not allowed", loc);
+            if (ASR::is_a<ASR::Var_t>(*e)) {
+                ASR::Variable_t* v = ASRUtils::EXPR2VAR(e);
+                if (v->m_intent == ASRUtils::intent_in) {
+                    throw SemanticError("Modifying input function parameter `"
+                                + std::string(v->m_name) + "` is not allowed", loc);
+                }
             }
         }
         auto search = attribute_map.find(key);