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[release/6.0] Port stackoverflow fix from Roslyn to SourceGenerator PolyFill #76946

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Oct 13, 2022
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[release/6.0] Port stackoverflow fix from Roslyn to SourceGenerator PolyFill #76946

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148 changes: 96 additions & 52 deletions src/libraries/Common/src/Roslyn/SyntaxValueProvider_ForAttributeWithSimpleName.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -215,7 +215,7 @@ private static ImmutableArray<SyntaxNode> GetMatchingNodes(

try
{
recurse(compilationUnit, ref localAliases, ref seenNames, ref results, ref attributeTargets);
processCompilationUnit(compilationUnit, ref localAliases, ref seenNames, ref results, ref attributeTargets);

if (results.Length == 0)
return ImmutableArray<SyntaxNode>.Empty;
Expand All @@ -229,7 +229,21 @@ private static ImmutableArray<SyntaxNode> GetMatchingNodes(
seenNames.Dispose();
}

void recurse(
void processCompilationUnit(
SyntaxNode compilationUnit,
ref Aliases localAliases,
ref ValueListBuilder<string> seenNames,
ref ValueListBuilder<SyntaxNode> results,
ref ValueListBuilder<SyntaxNode> attributeTargets)
{
cancellationToken.ThrowIfCancellationRequested();

syntaxHelper.AddAliases(compilationUnit, ref localAliases, global: false);

processCompilationOrNamespaceMembers(compilationUnit, ref localAliases, ref seenNames, ref results, ref attributeTargets);
}

void processCompilationOrNamespaceMembers(
SyntaxNode node,
ref Aliases localAliases,
ref ValueListBuilder<string> seenNames,
Expand All @@ -238,70 +252,100 @@ void recurse(
{
cancellationToken.ThrowIfCancellationRequested();

if (node is ICompilationUnitSyntax)
foreach (var child in node.ChildNodesAndTokens())
{
syntaxHelper.AddAliases(node, ref localAliases, global: false);

recurseChildren(node, ref localAliases, ref seenNames, ref results, ref attributeTargets);
if (child.IsNode)
{
var childNode = child.AsNode()!;
if (syntaxHelper.IsAnyNamespaceBlock(childNode))
processNamespaceBlock(childNode, ref localAliases, ref seenNames, ref results, ref attributeTargets);
else
processMember(childNode, ref localAliases, ref seenNames, ref results, ref attributeTargets);
}
}
else if (syntaxHelper.IsAnyNamespaceBlock(node))
{
var localAliasCount = localAliases.Length;
syntaxHelper.AddAliases(node, ref localAliases, global: false);
}

void processNamespaceBlock(
SyntaxNode namespaceBlock,
ref Aliases localAliases,
ref ValueListBuilder<string> seenNames,
ref ValueListBuilder<SyntaxNode> results,
ref ValueListBuilder<SyntaxNode> attributeTargets)
{
cancellationToken.ThrowIfCancellationRequested();

recurseChildren(node, ref localAliases, ref seenNames, ref results, ref attributeTargets);
var localAliasCount = localAliases.Length;
syntaxHelper.AddAliases(namespaceBlock, ref localAliases, global: false);

// after recursing into this namespace, dump any local aliases we added from this namespace decl itself.
localAliases.Length = localAliasCount;
}
else if (syntaxHelper.IsAttributeList(node))
processCompilationOrNamespaceMembers(
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What about this recursion? Can't you still have stackoverflow if some generated code has a lot of namespaces nested within each other?

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the goal is not to prevent all recursion, it's to prevent recursion on cases that occur in the wild in reasonable scenarios. So, a user having a highly recursive expression (like a + b+ c+ ...) happens in teh wild and is a problem. We do not see users having insanely deeply recursive namespaces. Roslyn itself does not guard against that here or for other recursive cases.

Note: this algorithm is hard to make 'fully recursive' due to how it pushes/pops state as it enters/exits namespaces. THat's why the namespace portion stays implicitly recursive, but the rest of the code becomes explicitly recursive.

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Yeah, my suggestion wasn't really to not make this recursive or to prevent recursion, but instead to protect against a stack overflow in places were it is likely to happen. If the answer is: we don't expect ever to get a stackoverflow here, then I'm fine with not guarding against it. My main concern is that this code is used by analyzers that automatically run on all projects, so if we ever think it may be possible to hit, we should be defensive. That is just my 2 cents.

namespaceBlock, ref localAliases, ref seenNames, ref results, ref attributeTargets);

// after recursing into this namespace, dump any local aliases we added from this namespace decl itself.
localAliases.Length = localAliasCount;
}

void processMember(
SyntaxNode member,
ref Aliases localAliases,
ref ValueListBuilder<string> seenNames,
ref ValueListBuilder<SyntaxNode> results,
ref ValueListBuilder<SyntaxNode> attributeTargets)
{
cancellationToken.ThrowIfCancellationRequested();

// nodes can be arbitrarily deep. Use an explicit stack over recursion to prevent a stack-overflow.
var nodeStack = new ValueListBuilder<SyntaxNode>(Span<SyntaxNode>.Empty);
nodeStack.Append(member);

try
{
foreach (var attribute in syntaxHelper.GetAttributesOfAttributeList(node))
while (nodeStack.Length > 0)
{
// Have to lookup both with the name in the attribute, as well as adding the 'Attribute' suffix.
// e.g. if there is [X] then we have to lookup with X and with XAttribute.
var simpleAttributeName = syntaxHelper.GetUnqualifiedIdentifierOfName(
syntaxHelper.GetNameOfAttribute(attribute)).ValueText;
if (matchesAttributeName(ref localAliases, ref seenNames, simpleAttributeName, withAttributeSuffix: false) ||
matchesAttributeName(ref localAliases, ref seenNames, simpleAttributeName, withAttributeSuffix: true))
{
attributeTargets.Length = 0;
syntaxHelper.AddAttributeTargets(node, ref attributeTargets);
var node = nodeStack.Pop();

foreach (var target in attributeTargets.AsSpan())
if (syntaxHelper.IsAttributeList(node))
{
foreach (var attribute in syntaxHelper.GetAttributesOfAttributeList(node))
{
if (predicate(target, cancellationToken))
results.Append(target);
// Have to lookup both with the name in the attribute, as well as adding the 'Attribute' suffix.
// e.g. if there is [X] then we have to lookup with X and with XAttribute.
var simpleAttributeName = syntaxHelper.GetUnqualifiedIdentifierOfName(
syntaxHelper.GetNameOfAttribute(attribute)).ValueText;
if (matchesAttributeName(ref localAliases, ref seenNames, simpleAttributeName, withAttributeSuffix: false) ||
matchesAttributeName(ref localAliases, ref seenNames, simpleAttributeName, withAttributeSuffix: true))
{
attributeTargets.Length = 0;
syntaxHelper.AddAttributeTargets(node, ref attributeTargets);

foreach (var target in attributeTargets.AsSpan())
{
if (predicate(target, cancellationToken))
results.Append(target);
}

break;
}
}

return;
// attributes can't have attributes inside of them. so no need to recurse when we're done.
}
else
{
// For any other node, just keep recursing deeper to see if we can find an attribute. Note: we cannot
// terminate the search anywhere as attributes may be found on things like local functions, and that
// means having to dive deep into statements and expressions.
foreach (var child in node.ChildNodesAndTokens().Reverse())
{
if (child.IsNode)
nodeStack.Append(child.AsNode()!);
}
}
}

// attributes can't have attributes inside of them. so no need to recurse when we're done.
}
else
{
// For any other node, just keep recursing deeper to see if we can find an attribute. Note: we cannot
// terminate the search anywhere as attributes may be found on things like local functions, and that
// means having to dive deep into statements and expressions.
recurseChildren(node, ref localAliases, ref seenNames, ref results, ref attributeTargets);
}
}

return;

void recurseChildren(
SyntaxNode node,
ref Aliases localAliases,
ref ValueListBuilder<string> seenNames,
ref ValueListBuilder<SyntaxNode> results,
ref ValueListBuilder<SyntaxNode> attributeTargets)
finally
{
foreach (var child in node.ChildNodesAndTokens())
{
if (child.IsNode)
recurse(child.AsNode()!, ref localAliases, ref seenNames, ref results, ref attributeTargets);
}
nodeStack.Dispose();
}
}

Expand Down