.

Author: SimonCropp

src/ApiBuilderTests/FrameworkSplitterTest.cs

@@ -95,6 +95,8 @@ void ProcessFile(string sourceFile, FrameworkIdentifier framework, string framew
         var lines = processedCode.Split('\n');
         var filteredLines = lines.Where(line => !line.TrimStart().StartsWith("//Link:", StringComparison.OrdinalIgnoreCase));
         processedCode = string.Join("\n", filteredLines);
+        // Simplify mixed #if conditions by removing always-true framework parts
+        processedCode = SimplifyPreprocessorConditions(processedCode, frameworkSymbols);
         var codeWithHeader = $"// <auto-generated />\n#pragma warning disable\n{processedCode}";
         File.WriteAllText(outputPath, codeWithHeader);
 
@@ -156,6 +158,121 @@ static SyntaxNode RemoveFrameworkDirectives(SyntaxNode root, List<string> featur
         return rewriter.Visit(root);
     }
 
+    // Simplify preprocessor conditions by removing always-true framework parts
+    // For example: "#if !NET8_0_OR_GREATER && FeatureX" becomes "#if FeatureX" when NET8_0_OR_GREATER is not defined
+    static string SimplifyPreprocessorConditions(string code, List<string> definedFrameworkSymbols)
+    {
+        var lines = code.Split('\n');
+        var result = new List<string>();
+
+        foreach (var line in lines)
+        {
+            var trimmed = line.TrimStart();
+            if (trimmed.StartsWith("#if ") || trimmed.StartsWith("#elif "))
+            {
+                var simplified = SimplifyConditionLine(line, definedFrameworkSymbols);
+                result.Add(simplified);
+            }
+            else
+            {
+                result.Add(line);
+            }
+        }
+
+        return string.Join("\n", result);
+    }
+
+    static string SimplifyConditionLine(string line, List<string> definedSymbols)
+    {
+        // Extract the directive and condition
+        var trimmed = line.TrimStart();
+        var leadingWhitespace = line[..^trimmed.Length];
+
+        string directive;
+        string condition;
+        if (trimmed.StartsWith("#if "))
+        {
+            directive = "#if ";
+            condition = trimmed[4..];
+        }
+        else if (trimmed.StartsWith("#elif "))
+        {
+            directive = "#elif ";
+            condition = trimmed[6..];
+        }
+        else
+        {
+            return line;
+        }
+
+        // Simplify the condition
+        var simplified = SimplifyCondition(condition, definedSymbols);
+
+        return $"{leadingWhitespace}{directive}{simplified}";
+    }
+
+    static string SimplifyCondition(string condition, List<string> definedSymbols)
+    {
+        var result = condition;
+
+        // Build a set of all framework-related symbols (both defined and potentially undefined)
+        var allFrameworkSymbols = new HashSet<string>
+        {
+            "NETFRAMEWORK", "NETSTANDARD", "NETCOREAPP", "NET",
+            "NET461", "NET462", "NET46X", "NET47", "NET471", "NET47X", "NET472", "NET48", "NET48X", "NET481",
+            "NET5_0", "NET6_0", "NET7_0", "NET8_0", "NET9_0", "NET10_0",
+            "NETCOREAPP2_0", "NETCOREAPP2_1", "NETCOREAPP2_2", "NETCOREAPP2X",
+            "NETCOREAPP3_0", "NETCOREAPP3_1", "NETCOREAPP3X",
+            "NETSTANDARD2_0", "NETSTANDARD2_1",
+            "NET5_0_OR_GREATER", "NET6_0_OR_GREATER", "NET7_0_OR_GREATER",
+            "NET8_0_OR_GREATER", "NET9_0_OR_GREATER", "NET10_0_OR_GREATER",
+            "NET461_OR_GREATER", "NET462_OR_GREATER", "NET47_OR_GREATER", "NET471_OR_GREATER",
+            "NET472_OR_GREATER", "NET48_OR_GREATER", "NET481_OR_GREATER",
+            "NETCOREAPP2_0_OR_GREATER", "NETCOREAPP2_1_OR_GREATER", "NETCOREAPP2_2_OR_GREATER",
+            "NETCOREAPP3_0_OR_GREATER", "NETCOREAPP3_1_OR_GREATER",
+            "NETSTANDARD2_0_OR_GREATER", "NETSTANDARD2_1_OR_GREATER",
+            "WINDOWS"
+        };
+
+        var definedSet = definedSymbols.ToHashSet();
+
+        // For each framework symbol, simplify based on whether it's defined
+        foreach (var symbol in allFrameworkSymbols)
+        {
+            var isDefined = definedSet.Contains(symbol);
+
+            if (isDefined)
+            {
+                // Symbol is defined (true)
+                // !SYMBOL is false - if part of &&, whole thing might be false (but BranchTaken would handle that)
+                // SYMBOL is true - can be removed from && chains
+                // Remove "SYMBOL && " or " && SYMBOL" patterns
+                result = System.Text.RegularExpressions.Regex.Replace(result, $@"\b{symbol}\b\s*&&\s*", "");
+                result = System.Text.RegularExpressions.Regex.Replace(result, $@"\s*&&\s*\b{symbol}\b", "");
+                // Handle standalone SYMBOL (entire condition is just the symbol)
+                if (result.Trim() == symbol)
+                {
+                    result = "true";
+                }
+            }
+            else
+            {
+                // Symbol is not defined (false)
+                // !SYMBOL is true - can be removed from && chains
+                // Remove "!SYMBOL && " or " && !SYMBOL" patterns
+                result = System.Text.RegularExpressions.Regex.Replace(result, $@"!\s*{symbol}\s*&&\s*", "");
+                result = System.Text.RegularExpressions.Regex.Replace(result, $@"\s*&&\s*!\s*{symbol}\b", "");
+                // Handle standalone !SYMBOL
+                if (System.Text.RegularExpressions.Regex.IsMatch(result.Trim(), $@"^!\s*{symbol}$"))
+                {
+                    result = "true";
+                }
+            }
+        }
+
+        return result.Trim();
+    }
+
     // Symbols to define during parsing (makes code active)
     // Excludes symbols that typically appear negated (like !RefsBclMemory)
     List<string> GetParseSymbols() =>

src/Split/net461/ArgumentExceptions/ArgumentNullExceptionPolyfill.cs

@@ -19,7 +19,7 @@ public static void ThrowIfNull([NotNull] object? argument, [CallerArgumentExpres
             }
         }
 
-#if AllowUnsafeBlocks && !NET9_0_OR_GREATER
+#if AllowUnsafeBlocks
 
         public static unsafe void ThrowIfNull(void* argument, [CallerArgumentExpression(nameof(argument))] string? paramName = null)
         {

src/Split/net461/OperatingSystemCache.cs

@@ -2,7 +2,7 @@
 #pragma warning disable
 namespace Polyfills;
 
-#if FeatureRuntimeInformation && !NET
+#if FeatureRuntimeInformation
 
 using System;
 using System.Diagnostics;

src/Split/net461/OperatingSystemPolyfill.cs

@@ -1,6 +1,6 @@
 // <auto-generated />
 #pragma warning disable
-#if !NET8_0_OR_GREATER && FeatureRuntimeInformation
+#if FeatureRuntimeInformation
 
 namespace Polyfills;
 

src/Split/net461/Polyfill_IEnumerable_ElementAt.cs

@@ -1,6 +1,6 @@
 // <auto-generated />
 #pragma warning disable
-#if FeatureValueTuple && !NET6_0_OR_GREATER
+#if FeatureValueTuple
 
 namespace Polyfills;
 

src/Split/net461/Polyfill_IEnumerable_Index.cs

@@ -1,6 +1,6 @@
 // <auto-generated />
 #pragma warning disable
-#if !NET9_0_OR_GREATER && FeatureValueTuple
+#if FeatureValueTuple
 namespace Polyfills;
 
 using System.Collections.Generic;

src/Split/net461/Polyfill_List.cs

@@ -14,7 +14,7 @@ static partial class Polyfill
     public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
         new(target);
 
-#if !NET8_0_OR_GREATER && FeatureMemory
+#if FeatureMemory
     /// <summary>Adds the elements of the specified span to the end of the <see cref="List{T}"/>.</summary>
 
     public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)

src/Split/net461/Polyfill_Memory_SpanSplitEnumerator.cs

@@ -1,6 +1,6 @@
 // <auto-generated />
 #pragma warning disable
-#if FeatureMemory && !NET9_0_OR_GREATER && FeatureValueTuple
+#if FeatureMemory && FeatureValueTuple
 
 namespace Polyfills;
 

src/Split/net461/Polyfill_Memory_SpanSplitEnumeratorMode.cs

@@ -1,6 +1,6 @@
 // <auto-generated />
 #pragma warning disable
-#if FeatureMemory && !NET9_0_OR_GREATER
+#if FeatureMemory
 
 namespace Polyfills;
 

src/Split/net461/Polyfill_Random.cs

@@ -78,7 +78,7 @@ public static T[] GetItems<T>(
     }
 
 
-#if !NETCOREAPP2_1_OR_GREATER && !NETSTANDARD2_1_OR_GREATER && FeatureMemory
+#if FeatureMemory
 
     /// <summary>
     /// Fills the elements of a specified span of bytes with random numbers.