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Fix a crash when reporting an error at the end of a file #310

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Oct 11, 2025
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Fix a crash when reporting an error at the end of a file #310

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3 changes: 2 additions & 1 deletion src/globals.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1395,7 +1395,8 @@ void error(char *msg)
start_idx = offset + 1;

for (offset = 0;
offset < MAX_SOURCE && SOURCE->elements[start_idx + offset] != '\n';
offset < MAX_SOURCE && (start_idx + offset) < SOURCE->size &&
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@cubic-dev-ai cubic-dev-ai bot Oct 10, 2025 •
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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>
Fix with Cubic

SOURCE->elements[start_idx + offset] != '\n';
offset++) {
diagnostic[i++] = SOURCE->elements[start_idx + offset];
}
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