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fix(assertions): stack overflow while parsing template #26767

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merged 2 commits into from
Aug 18, 2023
Merged

fix(assertions): stack overflow while parsing template #26767

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8469648
fix(assertions): stack overflow while parsing template
Chriscbr Aug 15, 2023
55f3239
Merge branch 'main' into fix-cyclic
mergify[bot] Aug 18, 2023
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4 changes: 2 additions & 2 deletions packages/aws-cdk-lib/assertions/lib/private/cyclic.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -167,12 +167,12 @@ function findCycle(deps: ReadonlyMap<string, ReadonlySet<string>>): string[] {

function recurse(node: string, path: string[]): string[] | undefined {
for (const dep of deps.get(node) ?? []) {
if (dep === path[0]) { return [...path, dep]; }
if (path.includes(dep)) { return [...path, dep]; }

const cycle = recurse(dep, [...path, dep]);
if (cycle) { return cycle; }
}

return undefined;
}
}
}
23 changes: 23 additions & 0 deletions packages/aws-cdk-lib/assertions/test/template.test.ts
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Expand Up @@ -1345,6 +1345,29 @@ describe('Template', () => {
}).toThrow(/dependency cycle/);
});

test('throws when given a more complex template with cyclic dependencies', () => {
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While i can see how the change in cyclic.ts makes the recurse function more efficient, this test isn't going to show that one way or another right? the test will succeed with the old code as well?

I'm prepared to just approve as is anyway, because this looks low risk and is hard to test, but want to make sure i have the whole picture first.

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I initially ran the test with the old code (unchanged) and it fails for me because of a stackoverflow error.
Screenshot 2023-08-17 at 5 46 06 PM

I think the call stack in the test case I added ends up looking like this (without the fix applied):

findCycle(deps)
recurse("Res1", ["Res1"])
recurse("Res2", ["Res1", "Res2"])
recurse("Res3", ["Res1", "Res2", "Res3"])
recurse("Res2", ["Res1", "Res2", "Res3", "Res2"])
recurse("Res3", ["Res1", "Res2", "Res3", "Res2", "Res3"])
...

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Ah i see

expect(() => {
Template.fromJSON({
Resources: {
Res1: {
Type: 'Foo',
Properties: {
Thing: { Ref: 'Res2' },
},
},
Res2: {
Type: 'Foo',
DependsOn: ['Res3'],
},
Res3: {
Type: 'Foo',
DependsOn: ['Res2'],
},
},
});
}).toThrow(/dependency cycle/);
});

test('does not throw when given a template with cyclic dependencies if check is skipped', () => {
expect(() => {
Template.fromJSON({
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