Added support for negative constant indexing in tuples (#1534)

* Added integration test
* Added tests to check for errors being thrown

Author: anutosh491

integration_tests/CMakeLists.txt

@@ -277,6 +277,7 @@ RUN(NAME test_list_10        LABELS cpython llvm c)
 RUN(NAME test_list_section   LABELS cpython llvm c)
 RUN(NAME test_tuple_01       LABELS cpython llvm c)
 RUN(NAME test_tuple_02       LABELS cpython llvm c)
+RUN(NAME test_tuple_03       LABELS cpython llvm)
 RUN(NAME test_dict_01        LABELS cpython llvm)
 RUN(NAME test_dict_02        LABELS cpython llvm)
 RUN(NAME test_dict_03        LABELS cpython llvm)

integration_tests/test_tuple_03.py

@@ -0,0 +1,10 @@
+from ltypes import i32, f64
+
+def f():
+    t1: tuple[i32, f64, str] = (1, 2.0, "3")
+
+    assert t1[-1] == "3"
+    assert t1[-2] == 2.0
+    assert t1[-3] == 1
+
+f()

src/lpython/semantics/python_ast_to_asr.cpp

@@ -3125,8 +3125,30 @@ class CommonVisitor : public AST::BaseVisitor<Struct> {
                                       ASR::down_cast<ASR::List_t>(type)->m_type, nullptr);
                 return false;
             } else if (ASR::is_a<ASR::Tuple_t>(*type)) {
+                int i = 0;
                 index = ASRUtils::EXPR(tmp);
-                int i = ASR::down_cast<ASR::IntegerConstant_t>(ASRUtils::EXPR(tmp))->m_n;
+                ASR::expr_t* val = ASRUtils::expr_value(index);
+                if (!val) {
+                    throw SemanticError("Runtime Indexing with " + ASRUtils::type_to_str_python(type) +
+                    " is not possible.", loc);
+                }
+
+                if (ASR::is_a<ASR::IntegerConstant_t>(*val)) {
+                    i = ASR::down_cast<ASR::IntegerConstant_t>(val)->m_n;
+                    int tuple_size =  ASR::down_cast<ASR::Tuple_t>(type)->n_type;
+                    if (i < 0) {
+                        i = tuple_size + i;
+                        ASR::ttype_t *int_type = ASRUtils::TYPE(ASR::make_Integer_t(al, loc,
+                                                        4, nullptr, 0));
+                        index = ASRUtils::EXPR(ASR::make_IntegerConstant_t(
+                            al, loc, i, int_type));
+                    }
+                    if (i >= tuple_size || i < 0) {
+                        throw SemanticError("Tuple index out of bounds", loc);
+                    }
+                } else {
+                    throw SemanticError("Tuple indices must be constant integers", loc);
+                }
                 tmp = make_TupleItem_t(al, loc, value, index,
                                        ASR::down_cast<ASR::Tuple_t>(type)->m_type[i], nullptr);
                 return false;

tests/errors/test_tuple2.py

@@ -0,0 +1,6 @@
+def main0():
+    t: tuple[i32, i32, i32] = (1, 2, 3)
+    x: i32 = -1
+    print(t[x])
+
+main0()

tests/errors/test_tuple3.py

@@ -0,0 +1,5 @@
+def main0():
+    t: tuple[i32, i32, i32] = (1, 2, 3)
+    print(t[-4])
+
+main0()

tests/reference/asr-test_tuple2-b046610.json

@@ -0,0 +1,13 @@
+{
+    "basename": "asr-test_tuple2-b046610",
+    "cmd": "lpython --show-asr --no-color {infile} -o {outfile}",
+    "infile": "tests/errors/test_tuple2.py",
+    "infile_hash": "84aa4ecdd21f5d633975d08f6927a7d336c47a31c2fd2bc42cae1c7b",
+    "outfile": null,
+    "outfile_hash": null,
+    "stdout": null,
+    "stdout_hash": null,
+    "stderr": "asr-test_tuple2-b046610.stderr",
+    "stderr_hash": "1e22bbde9c9fdc171314f1158dcac6bf6373d94e00c9878f66d7b667",
+    "returncode": 2
+}

tests/reference/asr-test_tuple2-b046610.stderr

@@ -0,0 +1,5 @@
+semantic error: Runtime Indexing with tuple[i32, i32, i32] is not possible.
+ --> tests/errors/test_tuple2.py:4:11
+  |
+4 |     print(t[x])
+  |           ^^^^ 

tests/reference/asr-test_tuple3-19fa47f.json

@@ -0,0 +1,13 @@
+{
+    "basename": "asr-test_tuple3-19fa47f",
+    "cmd": "lpython --show-asr --no-color {infile} -o {outfile}",
+    "infile": "tests/errors/test_tuple3.py",
+    "infile_hash": "cfa12cc4d8456bfd45e77cc49c5e8d2417181a1443cdaaf8b15c0528",
+    "outfile": null,
+    "outfile_hash": null,
+    "stdout": null,
+    "stdout_hash": null,
+    "stderr": "asr-test_tuple3-19fa47f.stderr",
+    "stderr_hash": "780d951c4bfa3476ee84d16d9a89c5a9255691b270bfb312d974608e",
+    "returncode": 2
+}

tests/reference/asr-test_tuple3-19fa47f.stderr

@@ -0,0 +1,5 @@
+semantic error: Tuple index out of bounds
+ --> tests/errors/test_tuple3.py:3:11
+  |
+3 |     print(t[-4])
+  |           ^^^^^ 

tests/tests.toml

@@ -896,6 +896,14 @@ asr = true
 filename = "errors/test_tuple1.py"
 asr = true
 
+[[test]]
+filename = "errors/test_tuple2.py"
+asr = true
+
+[[test]]
+filename = "errors/test_tuple3.py"
+asr = true
+
 [[test]]
 filename = "errors/test_for2.py"
 asr = true