Adding str slicing

Author: Abdullahjavednesar

integration_tests/test_str_01.py

@@ -25,9 +25,16 @@ def test_str_index():
     a = "012345"
     assert a[2] == "2"
 
+def test_str_slice():
+    a: str
+    a = "012345"
+    assert a[2:4] == "23"
+    assert a[2:3] == a[2]
+
 def check():
     f()
     test_str_concat()
     test_str_index()
+    test_str_slice()
 
 check()

src/libasr/codegen/asr_to_llvm.cpp

@@ -1079,15 +1079,17 @@ class ASRToLLVMVisitor : public ASR::BaseVisitor<ASRToLLVMVisitor>
                     //throw CodeGenError("Only string(a:b) for a,b variables for now.", x.base.base.loc);
                     // Use the "right" index for now
                     this->visit_expr_wrapper(x.m_args[0].m_right, true);
-                    llvm::Value *idx = tmp;
+                    llvm::Value *idx2 = tmp;
+                    this->visit_expr_wrapper(x.m_args[0].m_left, true);
+                    llvm::Value *idx1 = tmp;
                     // idx = builder->CreateSub(idx, llvm::ConstantInt::get(context, llvm::APInt(32, 1)));
                     //std::vector<llvm::Value*> idx_vec = {llvm::ConstantInt::get(context, llvm::APInt(32, 0)), idx};
                     // std::vector<llvm::Value*> idx_vec = {idx};
                     llvm::Value *str = CreateLoad(array);
                     // llvm::Value *p = CreateGEP(str, idx_vec);
                     // TODO: Currently the string starts at the right location, but goes to the end of the original string.
                     // We have to allocate a new string, copy it and add null termination.
-                    llvm::Value *p = lfortran_str_copy(str, idx, idx);
+                    llvm::Value *p = lfortran_str_copy(str, idx1, idx2);
 
                     tmp = builder->CreateAlloca(character_type, nullptr);
                     builder->CreateStore(p, tmp);

src/runtime/impure/lfortran_intrinsics.c

@@ -606,8 +606,11 @@ LFORTRAN_API void _lfortran_strcat(char** s1, char** s2, char** dest)
 
 // idx1 and idx2 both start from 1
 LFORTRAN_API char* _lfortran_str_copy(char* s, int32_t idx1, int32_t idx2) {
-    char* dest_char = (char*)malloc(idx2-idx1+2);
-    for (int i=idx1; i <= idx2; i++)
+    if (idx2 == idx1) {
+        idx2 = idx1 + 1;
+    }
+    char* dest_char = (char*)malloc(idx2-idx1+1);
+    for (int i=idx1; i < idx2; i++)
     {
         dest_char[i-idx1] = s[i-1];
     }