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Fix NullReferenceException when expanding property functions that return null #6414

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May 6, 2021
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Fix NullReferenceException when expanding property functions that return null #6414

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9 changes: 6 additions & 3 deletions src/Build.UnitTests/Evaluation/Expander_Tests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2010,13 +2010,16 @@ public void PropertyFunctionNullArgument()
public void PropertyFunctionNullReturn()
{
PropertyDictionary<ProjectPropertyInstance> pg = new PropertyDictionary<ProjectPropertyInstance>();
pg.Set(ProjectPropertyInstance.Create("SomeStuff", "This IS SOME STUff"));

Expander<ProjectPropertyInstance, ProjectItemInstance> expander = new Expander<ProjectPropertyInstance, ProjectItemInstance>(pg, FileSystems.Default);

string result = expander.ExpandIntoStringLeaveEscaped("$([System.Convert]::ChangeType(,$(SomeStuff.GetType())))", ExpanderOptions.ExpandProperties, MockElementLocation.Instance);
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Was this just a fancy way to get null before, and you're using the easier approach now?

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It was not evaluating to null before so not hitting the intended code path. Presumably because the (, argument omission makes us pass an empty string.


// The null-returning function is the only thing in the expression.
string result = expander.ExpandIntoStringLeaveEscaped("$([System.Environment]::GetEnvironmentVariable(`_NonExistentVar`))", ExpanderOptions.ExpandProperties, MockElementLocation.Instance);
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I'm now reminded that if an environment var doesn't exist, GetEnvironmentVariable returns null.

Assert.Equal("", result);

// The result of the null-returning function is concatenated with a non-empty string.
result = expander.ExpandIntoStringLeaveEscaped("prefix_$([System.Environment]::GetEnvironmentVariable(`_NonExistentVar`))", ExpanderOptions.ExpandProperties, MockElementLocation.Instance);
Assert.Equal("prefix_", result);
}

/// <summary>
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21 changes: 12 additions & 9 deletions src/Build/Evaluation/Expander.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1200,19 +1200,22 @@ private static class PropertyExpander<T>
propertyValue = LookupProperty(properties, expression, propertyStartIndex + 2, propertyEndIndex - 1, elementLocation, usedUninitializedProperties);
}

if (IsTruncationEnabled(options) && propertyValue != null)
if (propertyValue != null)
{
var value = propertyValue.ToString();
if (value.Length > CharacterLimitPerExpansion)
if (IsTruncationEnabled(options))
{
propertyValue = value.Substring(0, CharacterLimitPerExpansion - 3) + "...";
var value = propertyValue.ToString();
if (value.Length > CharacterLimitPerExpansion)
{
propertyValue = value.Substring(0, CharacterLimitPerExpansion - 3) + "...";
}
}
}

// Record our result, and advance
// our sourceIndex pointer to the character just after the closing
// parenthesis.
results.Add(propertyValue);
// Record our result, and advance
// our sourceIndex pointer to the character just after the closing
// parenthesis.
results.Add(propertyValue);
}
sourceIndex = propertyEndIndex + 1;
}

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