From df0b55763847e8fbb9e9cc3cce37776de74d6f68 Mon Sep 17 00:00:00 2001
From: Rangi <35663410+Rangi42@users.noreply.github.com>
Date: Sat, 11 Apr 2026 12:16:07 -0400
Subject: [PATCH] Don't allow invalid interpolations to occur (#1925)

Fixes #1921
---
 src/asm/lexer.cpp                       | 13 ++++++---
 test/asm/invalid-format.err             |  4 +--
 test/asm/invalid-format.out             |  4 +--
 test/asm/label-macro-arg.err            |  6 ++---
 test/asm/nested-brackets.err            |  2 +-
 test/asm/nested-brackets.out            |  2 +-
 test/asm/unterminated-interpolation.asm | 13 +++++++++
 test/asm/unterminated-interpolation.err | 36 +++++++++++++++++++++++++
 test/asm/unterminated-interpolation.out | 10 +++++++
 9 files changed, 77 insertions(+), 13 deletions(-)
 create mode 100644 test/asm/unterminated-interpolation.asm
 create mode 100644 test/asm/unterminated-interpolation.err
 create mode 100644 test/asm/unterminated-interpolation.out

diff --git a/src/asm/lexer.cpp b/src/asm/lexer.cpp
index 92b1aade..6739e90a 100644
--- a/src/asm/lexer.cpp
+++ b/src/asm/lexer.cpp
@@ -1320,6 +1320,7 @@ static std::pair<Symbol const *, std::shared_ptr<std::string>> readInterpolation
 
 	std::string identifier;
 	FormatSpec fmt{};
+	bool invalid = false;
 
 	for (;;) {
 		// Use `consumeChar()` since `peek()` might expand nested interpolations and recursively
@@ -1330,7 +1331,8 @@ static std::pair<Symbol const *, std::shared_ptr<std::string>> readInterpolation
 			}
 			continue; // Restart, reading from the new buffer
 		} else if (int c = peek(); c == EOF || isNewline(c) || c == '"') {
-			error("Missing '}'");
+			error("Unterminated interpolation");
+			invalid = true;
 			break;
 		} else if (c == '}') {
 			shiftChar();
@@ -1339,15 +1341,20 @@ static std::pair<Symbol const *, std::shared_ptr<std::string>> readInterpolation
 			shiftChar();
 			size_t n = fmt.parseSpec(identifier.c_str());
 			if (!fmt.isValid() || n != identifier.length()) {
-				error("Invalid format spec \"%s\"", identifier.c_str());
+				error("Invalid interpolation format spec \"%s\"", identifier.c_str());
+				invalid = true;
 			}
-			identifier.clear(); // Now that format has been set, restart at beginning of string
+			identifier.clear(); // Now that format has been set, restart at beginning of string.
 		} else {
 			shiftChar();
 			identifier += c;
 		}
 	}
 
+	if (invalid) {
+		return {nullptr, nullptr}; // Don't allow invalid interpolation to occur.
+	}
+
 	if (identifier.starts_with('#')) {
 		// Skip a '#' raw symbol prefix, but after expanding any nested interpolations.
 		identifier.erase(0, 1);
diff --git a/test/asm/invalid-format.err b/test/asm/invalid-format.err
index b62c621b..808b8c13 100644
--- a/test/asm/invalid-format.err
+++ b/test/asm/invalid-format.err
@@ -12,9 +12,9 @@ error: STRFMT: Invalid format spec for argument 2
     at invalid-format.asm(5)
 error: STRFMT: Invalid format spec for argument 3
     at invalid-format.asm(5)
-error: Invalid format spec "5d5"
+error: Invalid interpolation format spec "5d5"
     at invalid-format.asm(8)
-error: Invalid format spec "xx"
+error: Invalid interpolation format spec "xx"
     at invalid-format.asm(9)
 error: Formatting string with sign flag '+'
     at invalid-format.asm(11)
diff --git a/test/asm/invalid-format.out b/test/asm/invalid-format.out
index 633d8403..a14b199a 100644
--- a/test/asm/invalid-format.out
+++ b/test/asm/invalid-format.out
@@ -3,8 +3,8 @@ $2a %##x
 42   %--4d
 42 %..f
 42.00000 %q.16f %qq16f
-   42    42
-2a 2a
+   42 
+2a 
 hello
 hello
 hello
diff --git a/test/asm/label-macro-arg.err b/test/asm/label-macro-arg.err
index 1ad79c46..bae97dfe 100644
--- a/test/asm/label-macro-arg.err
+++ b/test/asm/label-macro-arg.err
@@ -10,8 +10,6 @@ error: syntax error, unexpected label, expecting symbol
     while expanding symbol `VAR_DEF`
 error: syntax error, unexpected label, expecting symbol
     at label-macro-arg.asm::test_char(26) <- label-macro-arg.asm(39)
-error: Invalid format spec "sizeof_"
+error: Invalid interpolation format spec "sizeof_"
     at label-macro-arg.asm::test_char(29) <- label-macro-arg.asm(39)
-error: Interpolated symbol `something` does not exist
-    at label-macro-arg.asm::test_char(29) <- label-macro-arg.asm(39)
-Assembly aborted with 7 errors
+Assembly aborted with 6 errors
diff --git a/test/asm/nested-brackets.err b/test/asm/nested-brackets.err
index b5fbc276..19f809e2 100644
--- a/test/asm/nested-brackets.err
+++ b/test/asm/nested-brackets.err
@@ -1,3 +1,3 @@
-error: Missing '}'
+error: Unterminated interpolation
     at nested-brackets.asm(5)
 Assembly aborted with 1 error
diff --git a/test/asm/nested-brackets.out b/test/asm/nested-brackets.out
index 2c94e483..885fd66b 100644
--- a/test/asm/nested-brackets.out
+++ b/test/asm/nested-brackets.out
@@ -1,2 +1,2 @@
 OK
-OK
+
diff --git a/test/asm/unterminated-interpolation.asm b/test/asm/unterminated-interpolation.asm
new file mode 100644
index 00000000..b73a681a
--- /dev/null
+++ b/test/asm/unterminated-interpolation.asm
@@ -0,0 +1,13 @@
+def x = 10
+println "{d:x", "!"
+println "{v:x", "?"
+println x, {d:x
+
+def name equs "x"
+println "{{name", "..."
+println "{v:{name}}!"
+println "{v:{name}?"
+println "{v:{name}", "?"
+println "{d:{v:name}}!?"
+println "{d:{v:name}?!"
+println "{d:{v:name}", "?!"
diff --git a/test/asm/unterminated-interpolation.err b/test/asm/unterminated-interpolation.err
new file mode 100644
index 00000000..ab2f5f8f
--- /dev/null
+++ b/test/asm/unterminated-interpolation.err
@@ -0,0 +1,36 @@
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(2)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(3)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(3)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(4)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(7)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(7)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(8)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(9)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(9)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(10)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(10)
+    while expanding symbol `name`
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(11)
+error: Interpolated symbol `` does not exist
+    at unterminated-interpolation.asm(11)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(12)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(12)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(13)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(13)
+Assembly aborted with 17 errors
diff --git a/test/asm/unterminated-interpolation.out b/test/asm/unterminated-interpolation.out
new file mode 100644
index 00000000..17d0d3e8
--- /dev/null
+++ b/test/asm/unterminated-interpolation.out
@@ -0,0 +1,10 @@
+!
+?
+$A
+...
+!
+
+?
+!?
+
+?!