Add support to process null in attributes
#3190
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- Checking for sentinel value in string ID creating a null string instance.
josesimoes
added
the
Area: Interpreter
WalkthroughThe update modifies the Changes
Sequence Diagram(s)sequenceDiagram
participant Caller
participant AttributeParser
participant StringInstance
Caller->>AttributeParser: ReadString(blob)
AttributeParser->>AttributeParser: Read token from blob
alt token == 0xFFFF
AttributeParser->>StringInstance: Create null string instance
else token != 0xFFFF
AttributeParser->>StringInstance: Create string instance from token
end
AttributeParser->>AttributeParser: Box string value
AttributeParser-->>Caller: Return boxed string
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Actionable comments posted: 1
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src/CLR/Core/TypeSystem.cpp(1 hunks)
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Comment on lines
+7186
to
+7195
| // check for invalid string ID: "null" string | ||
| if (tk == 0xFFFF) | ||
| { | ||
| // create a null string | ||
| NANOCLR_CHECK_HRESULT(CLR_RT_HeapBlock_String::CreateInstance(*value, nullptr, m_assm)); | ||
| } | ||
| else | ||
| { | ||
| NANOCLR_CHECK_HRESULT(CLR_RT_HeapBlock_String::CreateInstance(*value, CLR_TkFromType(TBL_Strings, tk), m_assm)); | ||
| } |
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🛠️ Refactor suggestion
Clarify handling of the 0xFFFF “null-string” sentinel
Nice addition, but two details are worth revisiting:
- Semantics –
CLR_RT_HeapBlock_String::CreateInstance(*value, nullptr, …)will still allocate aSystem.Stringobject (of length 0) rather than leaving theHeapBlockas anullreference. In C# terms this gives"", notnull.
If the intent is a truenull, consider:
- NANOCLR_CHECK_HRESULT(CLR_RT_HeapBlock_String::CreateInstance(*value, nullptr, m_assm));
+ value->SetObjectReference(nullptr); // real null
+ // boxing a null reference is a no-op, so skip PerformBoxing
+ return S_OK; // early-exit, nothing more to do(or update CreateInstance to return a null object explicitly).
- Magic number – Introduce a named constant (e.g.
c_STRING_TOKEN_NULL) instead of the raw0xFFFF; it documents intent and prevents accidental reuse.
+static constexpr CLR_UINT16 c_STRING_TOKEN_NULL = 0xFFFF;
...
- if (tk == 0xFFFF)
+ if (tk == c_STRING_TOKEN_NULL)These tweaks make the behaviour unambiguous and future-proof.
📝 Committable suggestion
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Suggested change
| // check for invalid string ID: "null" string | |
| if (tk == 0xFFFF) | |
| { | |
| // create a null string | |
| NANOCLR_CHECK_HRESULT(CLR_RT_HeapBlock_String::CreateInstance(*value, nullptr, m_assm)); | |
| } | |
| else | |
| { | |
| NANOCLR_CHECK_HRESULT(CLR_RT_HeapBlock_String::CreateInstance(*value, CLR_TkFromType(TBL_Strings, tk), m_assm)); | |
| } | |
| static constexpr CLR_UINT16 c_STRING_TOKEN_NULL = 0xFFFF; | |
| // check for invalid string ID: "null" string | |
| if (tk == c_STRING_TOKEN_NULL) | |
| { | |
| value->SetObjectReference(nullptr); // real null | |
| // boxing a null reference is a no-op, so skip PerformBoxing | |
| return S_OK; // early-exit, nothing more to do | |
| } | |
| else | |
| { | |
| NANOCLR_CHECK_HRESULT( | |
| CLR_RT_HeapBlock_String::CreateInstance( | |
| *value, | |
| CLR_TkFromType(TBL_Strings, tk), | |
| m_assm | |
| ) | |
| ); | |
| } |
🤖 Prompt for AI Agents
In src/CLR/Core/TypeSystem.cpp around lines 7186 to 7195, the handling of the
0xFFFF sentinel for a "null" string currently creates an empty string instance
instead of a true null reference. To fix this, modify the code to set the
HeapBlock to a null reference explicitly when tk equals 0xFFFF, avoiding
allocation of an empty string. Additionally, replace the magic number 0xFFFF
with a clearly named constant like c_STRING_TOKEN_NULL to improve code clarity
and maintainability.
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Description
Motivation and Context
null.How Has This Been Tested?
[DataRow(999, null)].[build with MDP buildId 56307]
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