From ad9b47b72fb664c518a8e55471c58a3e21986cd0 Mon Sep 17 00:00:00 2001
From: bmcq-0 <66541602+bmcq-0@users.noreply.github.com>
Date: Fri, 5 Nov 2021 16:24:30 -0400
Subject: [PATCH] Fold length operations when argument is a constant string
 (#141)

Co-authored-by: Arseny Kapoulkine <arseny.kapoulkine@gmail.com>
---
 Compiler/src/Compiler.cpp |  5 +++++
 tests/Compiler.test.cpp   | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/Compiler/src/Compiler.cpp b/Compiler/src/Compiler.cpp
index 7750a1d..4c86b6f 100644
--- a/Compiler/src/Compiler.cpp
+++ b/Compiler/src/Compiler.cpp
@@ -2900,6 +2900,11 @@ struct Compiler
                 break;
 
             case AstExprUnary::Len:
+                if (arg.type == Constant::Type_String)
+                {
+                    result.type = Constant::Type_Number;
+                    result.valueNumber = double(arg.valueString.size);
+                }
                 break;
 
             default:
diff --git a/tests/Compiler.test.cpp b/tests/Compiler.test.cpp
index bbac330..1389bfe 100644
--- a/tests/Compiler.test.cpp
+++ b/tests/Compiler.test.cpp
@@ -1168,6 +1168,17 @@ RETURN R0 1
 )");
 }
 
+TEST_CASE("ConstantFoldStringLen")
+{
+    CHECK_EQ("\n" + compileFunction0("return #'string', #'', #'a', #('b')"), R"(
+LOADN R0 6
+LOADN R1 0
+LOADN R2 1
+LOADN R3 1
+RETURN R0 4
+)");
+}
+
 TEST_CASE("ConstantFoldCompare")
 {
     // ordered comparisons