From 8ec3cfe07d0614747f6b05eb82ed4f6d7354aac8 Mon Sep 17 00:00:00 2001
From: "K. Lange" <klange@toaruos.org>
Date: Fri, 22 Jan 2021 08:38:36 +0900
Subject: [PATCH] Optimizations for f-strings

---
 src/compiler.c               | 15 ++++++++++-----
 test/testFStrings.krk        |  6 ++++++
 test/testFStrings.krk.expect |  6 ++++++
 3 files changed, 22 insertions(+), 5 deletions(-)
 create mode 100644 test/testFStrings.krk
 create mode 100644 test/testFStrings.krk.expect

diff --git a/src/compiler.c b/src/compiler.c
index 87863c9..a35b4db 100644
--- a/src/compiler.c
+++ b/src/compiler.c
@@ -1770,8 +1770,11 @@ static void string(int type) {
 				}
 				c += 2;
 			} else if (isFormat && *c == '{') {
-				emitConstant(OBJECT_VAL(krk_copyString(stringBytes,stringLength)));
-				if (atLeastOne) emitByte(OP_ADD);
+				if (!atLeastOne || stringLength) { /* Make sure there's a string for coersion reasons */
+					emitConstant(OBJECT_VAL(krk_copyString(stringBytes,stringLength)));
+					if (atLeastOne) emitByte(OP_ADD);
+					atLeastOne = 1;
+				}
 				stringLength = 0;
 				KrkScanner beforeExpression = krk_tellScanner();
 				Parser  parserBefore = parser;
@@ -1814,7 +1817,7 @@ static void string(int type) {
 					error("Expected closing } after expression in f-string");
 					goto _cleanupError;
 				}
-				emitByte(OP_ADD);
+				if (atLeastOne) emitByte(OP_ADD);
 				atLeastOne = 1;
 				c++;
 			} else {
@@ -1839,9 +1842,11 @@ static void string(int type) {
 		emitConstant(OBJECT_VAL(bytes));
 		return;
 	}
-	emitConstant(OBJECT_VAL(krk_copyString(stringBytes,stringLength)));
+	if (!isFormat || stringLength || !atLeastOne) {
+		emitConstant(OBJECT_VAL(krk_copyString(stringBytes,stringLength)));
+		if (atLeastOne) emitByte(OP_ADD);
+	}
 	FREE_ARRAY(char,stringBytes,stringCapacity);
-	if (isFormat && atLeastOne) emitByte(OP_ADD);
 #undef PUSH_CHAR
 	return;
 _cleanupError:
diff --git a/test/testFStrings.krk b/test/testFStrings.krk
new file mode 100644
index 0000000..5e9bb5e
--- /dev/null
+++ b/test/testFStrings.krk
@@ -0,0 +1,6 @@
+print(f"Regular string")
+print(f"{1 + 2}")
+print(f"{1 + 2} with a string after")
+print(f"with a string before {1 + 2}")
+print(f"with {1+2}{object} nothing in between")
+print(f"{1 + 2}{3 + 4}{[]}{{}} with some fun expressions")
diff --git a/test/testFStrings.krk.expect b/test/testFStrings.krk.expect
new file mode 100644
index 0000000..60c7e9c
--- /dev/null
+++ b/test/testFStrings.krk.expect
@@ -0,0 +1,6 @@
+Regular string
+3
+3 with a string after
+with a string before 3
+with 3<type 'object'> nothing in between
+37[]{} with some fun expressions