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fix: return error instead of panic for missing frontmatter fence #1137

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Merged
matthewp merged 2 commits into from
Feb 3, 2026
Merged

fix: return error instead of panic for missing frontmatter fence #1137

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2b0ba68
fix: return error instead of panic for missing frontmatter fence
matthewp Feb 2, 2026
9dbe356
Add test for location
matthewp Feb 3, 2026
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5 changes: 5 additions & 0 deletions .changeset/fix-missing-frontmatter-fence.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@astrojs/compiler": patch
---

Fixes a panic when parsing files with a closing frontmatter fence (---) but no opening fence. The compiler now returns a helpful diagnostic error instead of crashing.
1 change: 1 addition & 0 deletions internal/loc/diagnostics.go
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Expand Up @@ -9,6 +9,7 @@ const (
ERROR_UNMATCHED_IMPORT DiagnosticCode = 1003
ERROR_UNSUPPORTED_SLOT_ATTRIBUTE DiagnosticCode = 1004
ERROR_UNTERMINATED_STRING DiagnosticCode = 1005
ERROR_MISSING_FRONTMATTER_FENCE DiagnosticCode = 1006
WARNING DiagnosticCode = 2000
WARNING_UNTERMINATED_HTML_COMMENT DiagnosticCode = 2001
WARNING_UNCLOSED_HTML_TAG DiagnosticCode = 2002
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13 changes: 13 additions & 0 deletions internal/parser.go
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Expand Up @@ -1103,6 +1103,19 @@ func copyAttributes(dst *Node, src Token) {
func inBodyIM(p *parser) bool {
switch p.tok.Type {
case FrontmatterFenceToken:
// If originalIM is already set, we have a closing fence without an opening one
if p.originalIM != nil {
p.handler.AppendError(&loc.ErrorWithRange{
Code: loc.ERROR_MISSING_FRONTMATTER_FENCE,
Text: "The closing frontmatter fence (---) is missing an opening fence",
Hint: "Add --- at the beginning of your file before any import statements or code",
Range: loc.Range{
Loc: p.tok.Loc,
Len: 3,
},
Comment on lines +1112 to +1115
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@ematipico ematipico Feb 3, 2026

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Do we have snapshot tests so that we can verify that the range is correct?

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@matthewp matthewp Feb 3, 2026

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We don't have a way to do snapshots of errors, so instead I added an assertion to the test I created here: 9dbe356

})
return true
}
p.setOriginalIM()
p.im = frontmatterIM
return false
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1 change: 1 addition & 0 deletions internal/token.go
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Expand Up @@ -1886,6 +1886,7 @@ frontmatter_loop:
case FrontmatterInitial:
z.fm = FrontmatterOpen
z.dashCount = 0
z.data.Start = z.raw.End - len("---")
z.data.End = z.raw.End
z.tt = FrontmatterFenceToken
z.openBraceIsExpressionStart = false
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44 changes: 44 additions & 0 deletions packages/compiler/test/errors/missing-frontmatter-fence.ts
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@@ -0,0 +1,44 @@
import { type TransformResult, transform } from '@astrojs/compiler';
import { test } from 'uvu';
import * as assert from 'uvu/assert';

// Missing opening frontmatter fence - only has closing ---
const FIXTURE = `import BaseLayout from '@/layouts/BaseLayout.astro';
import { getCollection } from 'astro:content';
const posts = await getCollection('blog');
---
<BaseLayout title="Crash Test">
<h1>{posts.length}</h1>
</BaseLayout>`;

let result: TransformResult;
test.before(async () => {
result = await transform(FIXTURE, {
filename: '/src/pages/checkthis.astro',
});
});

test('missing opening frontmatter fence reports error instead of panic', () => {
assert.ok(Array.isArray(result.diagnostics));
assert.is(result.diagnostics.length, 1);
assert.is(result.diagnostics[0].code, 1006);
assert.is(
result.diagnostics[0].text,
'The closing frontmatter fence (---) is missing an opening fence'
);
assert.is(
result.diagnostics[0].hint,
'Add --- at the beginning of your file before any import statements or code'
);
// Verify the error location points to the closing --- fence
const loc = result.diagnostics[0].location;
// The line number should point to the line containing ---
assert.is(FIXTURE.split('\n')[loc.line - 1], '---');
// The column and length should extract exactly the --- characters
assert.is(
FIXTURE.split('\n')[loc.line - 1].slice(loc.column - 1, loc.column - 1 + loc.length),
'---'
);
});

test.run();
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