From 86b43ea14f722ff0ca49908a7d9423eeeee12882 Mon Sep 17 00:00:00 2001
From: Rangi42 <sylvie.oukaour+rangi42@gmail.com>
Date: Thu, 31 Jul 2025 15:17:11 -0400
Subject: [PATCH] Fix interpolation after empty string literal

---
 src/asm/lexer.cpp                       | 15 ++++++++++++---
 test/asm/interpolation-after-string.err | 18 ++++--------------
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/src/asm/lexer.cpp b/src/asm/lexer.cpp
index 4ed76496..50d2811a 100644
--- a/src/asm/lexer.cpp
+++ b/src/asm/lexer.cpp
@@ -1219,7 +1219,9 @@ static std::shared_ptr<std::string> readInterpolation(size_t depth) {
 		// `lexerState->peekChar()` lets `readInterpolation()` handle its own nested expansions,
 		// increasing `depth` each time.
 		if (lexerState->peekChar() == '{') {
-			++lexerState->expansionScanDistance; // Prevent `shiftChar()` from calling `peek()`
+			// Increment `lexerState->expansionScanDistance` to prevent `shiftChar()` from calling
+			// `peek()` and to balance its decrement.
+			++lexerState->expansionScanDistance;
 			shiftChar();
 			if (std::shared_ptr<std::string> str = readInterpolation(depth + 1); str) {
 				beginExpansion(str, *str);
@@ -1425,12 +1427,19 @@ static void readString(std::string &str, bool rawString) {
 		if (rawMode) {
 			str += '"';
 		}
-		if (nextChar() != '"') {
+		shiftChar();
+		// `peek()` would mark the third character here as "painted blue" whether or not it is a
+		// third quote, which would incorrectly prevent expansions right after an empty string "".
+		// `lexerState->peekChar()` avoids this, and is okay since expansions are disabled here.
+		if (lexerState->peekChar() != '"') {
 			// "" is an empty string, skip the loop
 			return;
 		}
-		// """ begins a multi-line string
+		// Increment `lexerState->expansionScanDistance` to prevent `shiftChar()` from calling
+		// `peek()` and to balance its decrement.
+		++lexerState->expansionScanDistance;
 		shiftChar();
+		// """ begins a multi-line string
 		if (rawMode) {
 			str += '"';
 		}
diff --git a/test/asm/interpolation-after-string.err b/test/asm/interpolation-after-string.err
index 6e123fe9..187d35a0 100644
--- a/test/asm/interpolation-after-string.err
+++ b/test/asm/interpolation-after-string.err
@@ -1,18 +1,8 @@
-error: interpolation-after-string.asm(2):
-    Unknown character '{'
-error: interpolation-after-string.asm(2):
-    Unknown character '}'
-error: interpolation-after-string.asm(5):
-    Unknown character '{'
 error: interpolation-after-string.asm(5):
     syntax error, unexpected symbol
-while expanding symbol "greeting"
-error: interpolation-after-string.asm(5):
-    Unknown character '}'
+while expanding symbol "hello"
 error: interpolation-after-string.asm(8):
-    Unknown character '{'
+    Interpolated symbol "goodbye" does not exist
 error: interpolation-after-string.asm(8):
-    syntax error, unexpected symbol
-error: interpolation-after-string.asm(8):
-    Unknown character '}'
-Assembly aborted with 8 errors!
+    syntax error, unexpected string
+Assembly aborted with 3 errors!