Mutating the DefaultValueExpression is enough here; ConvertTo already hands
out mutated input nodes elsewhere (UnwrapChild), so building a replacement
node and copying the annotations over bought nothing.
The operator special case is easy to mistake for a cosmetic preference,
because the null literal is accepted in the same position: it converts only
to reference and nullable types, so it still narrows operator overload
resolution, whereas the default literal converts to everything and C#
rejects it outright for every binary operator except == and !=.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Shortening default(T) is the same problem as removing the redundant cast
around a lambda whose delegate type the context already fixes, so it uses
the same mechanism: ConvertTo makes the explicit type implicit when the
conversion is an identity conversion and the caller allows an implicit
one. The literal keeps the type it was shortened from, so any later
conversion to a different type - or any context that requires an explicit
type, such as an overload resolution recheck falling back to CastArguments
- can spell default(T) out again. That keeps the value intact where the
bare literal would change it, e.g. "object o = default(SomeStruct)", which
boxes a non-null struct while "default" would be null.
Because the shortened literal resolves to DefaultLiteralResolveResult,
CallBuilder's existing overload resolution recheck sees a real default
literal and rejects ambiguous calls on its own; no separate bookkeeping
about which arguments may stay untyped is needed. Only the contexts that
supply no target type at all restore the explicit form: an awaited
expression, and arguments of operator methods, which later become operator
or cast syntax rather than calls.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The C# 14 compiler lowers implicit span conversions to calls -
MemoryExtensions.AsSpan(string), ReadOnlySpan<T>.CastUp, and the span
op_Implicit operators - so decompiled code showed the lowered form even
though the conversion and betterness layers already implement the C# 14
rules. CallBuilder now folds those helper calls back into conversions,
riding the existing mechanism: the conversion is built as an explicit
cast, consumption sites make it implicit where the context allows, and
the overload-resolution recheck re-adds a cast when the bare argument
would bind to a different overload (which canonicalizes deliberate
AsSpan disambiguations to the equivalent explicit span cast).
Span conversions compose, so CastCanBeMadeImplicit lets a direct
input-to-target span conversion replace a chained pair; and an rvalue
bound to an in parameter gets the same chance to shed the cast as a
by-value argument, since ChangeDirectionExpressionTo bypasses the
by-value strip.
Part of #829.
Assisted-by: Claude:claude-fable-5:Claude Code
Overload resolution reports no error for an empty candidate set - there is
no best candidate to attach one to - so the null result passed for success
and was dereferenced while checking the call target. Decompiling
FSharp.DataFrame from nuget.org crashes that way: F# compiles its comparison
members to instance methods carrying operator metadata names, and the
operator candidate search looks at the operand types rather than at the
receiver type the member belongs to.
The new fixture pins that such an assembly decompiles at all. It still
renders those instance methods as operators and drops the receiver at the
call sites, which is the misclassification behind the empty candidate set
and is handled separately; this is the guard that keeps an empty candidate
set from being read as a resolved call.
Assisted-by: Claude:claude-opus-5:Claude Code
When a null literal is the only argument a generic type argument could
be inferred from, and that type argument is an anonymous type, ILSpy
used to drop the type arguments entirely (they cannot be written
explicitly), producing 'Test(null)', which no longer compiles
(CS0411). A conditional expression whose never-taken branch creates an
instance of the anonymous type is the minimal C# expression that gives
a null value that type, so the argument now carries enough information
for type inference.
The instance expression is obtained by translating a synthesized
'newobj' with 'default.value' arguments through the existing pipeline
rather than assembling syntax by hand; the property values are typed
defaults, since the IL only contains ldnull. Anonymous types occurring
inside other constructed types (e.g. arrays) stay unexpressible and
keep the previous output.
Assisted-by: Claude:claude-fable-5:Claude Code
F# emits tail calls pervasively, but the 'tail.' prefix was dropped
entirely at the C# output stage, so the information never reached the
decompiled text. Render it inline as '/*tail.*/' before the call,
mirroring the existing 'constrained.' prefix comment in CallBuilder.
Fix#3817
Assisted-by: Claude:claude-opus-4-8:Claude Code
The C# syntax tree's name accessors (ParameterDeclaration.Name, GotoStatement.Label,
catch variable, query continuations, ...) are convenience strings over a backing Identifier
token. Names that may be absent are now typed string? and read as null when absent, instead of
a non-null empty-string sentinel; required names stay non-null string. The backing token slot's
nullability follows, and an empty or null assignment clears the token (empty == absent).
Because the property type now carries optionality, the separate [NameSlot] attribute and its
nullOnEmpty flag are redundant: a [Slot] on a string property is a name (child slots are
AstNode-typed, so the type disambiguates), and the generator infers optionality from the
declared nullable annotation -- which a string? declaration already requires #nullable for. The
repeated empty-to-null setter body becomes Identifier.CreateIfNotEmpty. To make the annotation
readable, #nullable enable is turned on across the syntax node files (the directive the inferred
optionality depends on), with the attendant local nullability fixups. Consumers that feed a name
into a non-null slot assert it where the variable structurally has a name.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Turn on #nullable enable across the AST consumer layer: the output visitor, the
IL-to-C# builders (statement, call and expression builders, CSharpDecompiler,
TypeSystemAstBuilder), the translation-result wrappers, the sequence-point and
required-namespace collectors, and the annotation helpers. Optional inputs,
fields and returns are typed nullable, detector out-parameters use
[NotNullWhen(true)], and structurally-guaranteed dereferences use the
null-forgiving operator. A few public parameters that already tolerate null are
widened to match their downstream callers. The annotations emit no IL, so the
Pretty suite stays byte-identical.
Assisted-by: Claude:claude-opus-4-8:Claude Code
With every optional slot nullable, the null-object pattern is dead. Generated
non-nullable getters return the backing field directly, which surfaced a last
tier of slots the decompiler legitimately leaves empty (omitted range operands,
an implicitly-typed array creation, unnamed parameters, an unbound generic
argument, and others) and flips them to nullable too. The machinery is then
removed entirely: the per-node null classes, the .Null statics and
VisitNullNode, AstNode.IsNull, the role null object, and Identifier.Null.
AcceptVisitor becomes unconditionally generated, and consumers move from
.IsNull to is null and from unconditional visits to ?.AcceptVisitor.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Optional single-child slots return T? with a real null instead of a role
null-object, taking the C# grammar as the oracle for which slots are optional.
The generator emits the property type as T? and matches it with MatchOptional,
and consumers move from .IsNull to is null / ?.. This covers the optional
statement, member, try-catch, creation-initializer and pattern slots and the
optional NameSlot tokens. A few slots the grammar marks required but the
decompiler legitimately leaves empty (the implicit-element-access target, an
implicitly-typed lambda parameter's type) are flipped to nullable as well.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Comments and preprocessor directives were positional children interleaved
into the child list, and punctuation, keywords and operators were token-node
children. Add a leading/trailing trivia side-channel for comments and
directives, emit it from the output visitor, and re-home every comment
receiver onto it (including inside-block comments as comment-only empty
statements and undecodable attribute arguments as an ErrorExpression). With
locations and sequence points no longer sourced from token nodes, stop
reconstructing them on the locations path and delete CSharpTokenNode,
CSharpModifierToken and InsertSpecialsDecorator. The AST no longer carries
token children or positional comments; output is byte-identical.
Assisted-by: Claude:claude-opus-4-8:Claude Code
Christoph Wille
Daniel Grunwald
Siegfried Pammer
Peter Crabtree
Maximilian Schmöcker
Standa Lukeš