Steps to reproduce:

Create a VFX using the Simple Loop template and open it.
Drag the VFX asset into the scene and check the Console.
Add a Custom HLSL block to Update Particle.
Click the block's Edit button to open HLSL Editor.
Replace the entire default code with the function below.
Put your cursor before void and enter a new line or press Space key. This will move function declaration to a 2nd line or add a space before function declaration.
Click the save icon inside HLSL Editor, then save the graph.
Observe errors in the console

Function for pasting:

void F(inout VFXAttributes attributes)
{
    attributes.position.y = max(attributes.position.y, 0);
}

Actual results:
Leading whitespace corrupts the parsed function body. With one leading newline, an extra closing parenthesis is copied before the opening brace, producing invalid shader code.

Shader error in '[New VFX 5] [Simple Loop] Update Particles': syntax error: unexpected token ')' at kernel CSMain at line 152 (on metal)

[New VFX 5] [Simple Loop] Update Particles.compute: Kernel at index (0) is invalid
UnityEngine_CoreModule_ProxyFunctionPointers.UnityEngine_StackTraceUtility_ExtractStackTrace_UnmanagedCallers(ManagedSpanWrapper*, IntPtr)

Expected results:
Leading whitespace does not change the parsed function body or prevent compilation.

FAVs (PR in comments):

6000.5.0a9 → 6000.6.0a1

6000.4.11f1 → 6000.4.12f1

6000.5.0b11 → 6000.5.0f1

Not reproducible with versions:
None established.

Untested versions:

Tested on (OS):
macOS (Metal).

Notes:

Save inside HLSL Editor before saving the graph
Workaround: remove all leading whitespace before the first function declaration.
HLSLFunction.Parse() in HLSLParser.cs matches against hlsl.Trim(), but uses the resulting offsets to extract the function body from the original untrimmed hlsl string.
Parser controls with no leading whitespace and with a leading single-line comment produced the correct body.
The existing Editor log reported Unexpected directive followed by Kernel at index (0) is invalid. That particular diagnostic has not been isolated solely to this parser defect.