Fix a crash when reporting an error at the end of a file

[visitorckw]

The compiler crashes with a segmentation fault when an unterminated C-style comment exists at the very end of a file.

The root cause is a buffer over-read in the error() function, which attempts to construct a diagnostic message by reading the source line containing the error. When the error is on the last line of a file without a trailing newline, this logic would read past the end of the source buffer.

Fix the issue by adding a bounds check to the loop, ensuring it does not read beyond the source buffer's size. This allows the compiler to correctly report the "Unenclosed C-style comment" error instead of crashing.

---

Summary by cubic

Prevents a crash when reporting an error at EOF by adding a source-bounds check while building the diagnostic line. Unterminated C-style comments at the end of a file without a trailing newline now produce a proper error instead of a segfault.

• Bug Fixes
  • Add bounds check in error() to avoid reading past SOURCE->size when scanning for newline in src/globals.c.

[visitorckw]

FWIW, this issue can be easily reproduced with the following example:

int main() {
    /* this is an unterminated comment
}

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="src/globals.c">

<violation number="1" location="src/globals.c:1398">
This loop initializes `offset` to `SOURCE-&gt;size`, which causes an out-of-bounds read on the first iteration when accessing `SOURCE-&gt;elements[offset]`. The loop should initialize `offset` to `SOURCE-&gt;size - 1` to access the last valid element.</violation>
</file>

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[cubic-dev-ai]

This loop initializes offset to SOURCE->size, which causes an out-of-bounds read on the first iteration when accessing SOURCE->elements[offset]. The loop should initialize offset to SOURCE->size - 1 to access the last valid element.

Prompt for AI agents

Address the following comment on src/globals.c at line 1398:

<comment>This loop initializes `offset` to `SOURCE-&gt;size`, which causes an out-of-bounds read on the first iteration when accessing `SOURCE-&gt;elements[offset]`. The loop should initialize `offset` to `SOURCE-&gt;size - 1` to access the last valid element.</comment>

<file context>
@@ -1395,7 +1395,8 @@ void error(char *msg)
 
     for (offset = 0;
-         offset &lt; MAX_SOURCE &amp;&amp; SOURCE-&gt;elements[start_idx + offset] != &#39;\n&#39;;
+         offset &lt; MAX_SOURCE &amp;&amp; (start_idx + offset) &lt; SOURCE-&gt;size &amp;&amp;
+         SOURCE-&gt;elements[start_idx + offset] != &#39;\n&#39;;
          offset++) {
</file context>

[jserv]

Thank @visitorckw for contributing!