C# 12 allows both on the explicitly typed parameter list of a lambda, and
nowhere else: an anonymous method cannot declare either, and neither can a
lambda whose parameter list is about to be dropped. Guarded by a setting so
the output stays valid for earlier language versions.
Only what the anonymous function's own metadata declares is written. A lambda
may state a default the delegate does not have, a different one, or none where
the delegate has one, and reflection over the lambda's method reports what the
lambda declared - so filling either in from the delegate's Invoke would make
the recompiled assembly describe itself differently from the original. Call
sites are unaffected either way, because they bind against the delegate, which
still declares both.
Roslyn writes ParamArrayAttribute on the anonymous function's own method only
from version 5 on; before that it stands on the delegate type alone, where it
is not the lambda's to restate, so the fixture guards those cases on ROSLYN5.
The correctness test reads the metadata back through reflection, which is the
only place the difference is observable.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The C# 10 grammar only allows attributes on a lambda or its parameters
when the parameter list is parenthesized, but LambdaNeedsParenthesis
predates attribute support and only considered the single parameter's
type and modifiers. An attributed lambda whose parameter type is erased
for being anonymous therefore printed as '[My] a => a.X', which does not
parse. Latent since attributed-lambda decompilation was added: every
other attributed lambda has explicitly typed parameters, which already
force the parenthesized form.
Assisted-by: Claude:claude-fable-5:Claude Code
Invariants that involve types (stack type of a variable against its IType,
the element type of an array access, the operand types of a comparison)
need a type system to resolve them against, and the only correct one is the
type system the instruction tree was decoded with. Until now CheckInvariant
took only the phase, so such a check had no compilation to use:
DeconstructInstruction.CheckInvariant called IsAssignment with a null type
system, which only held up because the targets it sees are ldloc, whose
InferType never touches the compilation; a ldflda-wrapped or pointer target
would have failed inside the invariant instead of reporting a violation.
Every call site already has that type system in scope: the ILReader's
compilation, the ILTransformContext of the running transform, or the
decompiler's own IDecompilerTypeSystem. It is now passed explicitly and the
base implementation asserts it is present, so a future invariant can rely
on it without re-plumbing the callers.
Assisted-by: Claude:claude-fable-5:Claude Code
This way, we don't need the MapToMergedBounds logic to split the merged list back into lower/upper.
Also, this commit avoids the quadratic merge-everything-with-everything else -- instead we use a dictionary to compare only types that are equivalent to begin with.
This is the same approach as Roslyn MethodTypeInference.Fix/AddAllCandidates.
NullPropagationTransform only rewrites "x != null ? x.Chain : fallback"
into "x?.Chain ?? fallback" when the chain's inferred type is a
non-nullable value type, and InferType had no case for ldlen. Array length
therefore came back as UnknownType, so "arr?.Length ?? 0" was left as a
ternary.
The inferred type mirrors ExpressionBuilder.VisitLdLen, which decides
between Array.Length and Array.LongLength from the result type alone.
Found while investigating #3704, where the surviving ternary also keeps the
tested array in a stack slot and strands the typeof of a dynamic call's
static target. That issue is fixed separately in #4072, whose DynamicTests
cases pinned the ternary as expected output; those blocks round-trip
exactly now, so they are gone.
Also carries a review follow-up that missed #4072: the static-target test
in VisitDynamicInvokeMemberInstruction is a plain null check, the way
DynamicInvokeMemberInstruction itself tests the field, rather than a
pattern match binding a name it does not need.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
A local function nested in a lambda can capture closures at two depths:
csc emits it as an instance method on the enclosing method's display
class that takes the lambda's display class as a parameter. Combining
those two capture scopes with FindCommonAncestorInstruction picked the
enclosing method, moving the function out of the lambda that owns the
deeper closure; the variables captured there were then unreachable and
the display-class parameter survived into the output as an undeclared
identifier. Nested capture scopes resolve to the innermost instead,
which a local function can always see - it reaches the outer closure
through the display class it is declared on.
Assisted-by: Claude:claude-fable-5:Claude Code
Three places decided independently whether a backing field would still be
declared, and they disagreed. ReplaceBackingFieldUsage rewrote a constructor
store into a property assignment whenever the property looked collapsible,
without asking whether PatternStatementTransform would actually remove the
declaration; ConvertField printed the "field" keyword on the FieldKeyword
setting alone, ignoring the GetterOnlyAutomaticProperties veto that
MemberIsHidden applies to the same field.
Two consequences, both silent. A setter-less property under
GetterOnlyAutomaticProperties = false kept its declaration and got "field" in
the getter anyway, so the keyword bound to a second synthesized field and the
declared one went unwritten. A settable property under AutomaticProperties =
false had its initializing store turned into a property assignment that
TransformFieldAndConstructorInitializers could no longer lift, leaving the
constructor in the output with an unconverted base-constructor call.
BackingFieldWillBeRemoved is now the single verdict every branch consults, and
it mirrors the transform's own entry gate. A property that keeps explicit
accessors is no longer addressed by name: the store stays a field reference and
becomes the property initializer, which is what field-backed storage means. The
one exception is a setter-less property's constructor store, which C# allows to
be written as an assignment and which has no other expressible form.
IsBackingFieldOfAutomaticProperty now answers through TryGetBackingField instead
of its own name check, so the two directions of "is this field that property's
storage" cannot diverge on staticness or field type. ReplaceBackingFieldUsage
dispatches on the resolve result rather than the identifier's spelling; after
ConvertField the same field appears both as "field" and under its metadata name
carrying the same annotation, so matching the name was matching the wrong thing.
The keyword's own precondition moves into a CanUseFieldKeyword local function.
Seven clauses with comment blocks wedged between them had to be read as one
expression; as one early return per rule the list reads in order.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
ExpressionBuilder.ConvertField prints the C# 14 "field" keyword based on the
FieldKeyword setting alone, but PatternStatementTransform only entered the
property transform when AutomaticProperties was on. With FieldKeyword on and
AutomaticProperties off the backing-field declaration was therefore never
removed, and the output declared the backing field next to accessors already
written in terms of "field".
That output still compiles, which is what makes it dangerous: the keyword binds
to a second, freshly synthesized backing field while the declared one stays
unwritten, so the recompiled assembly has different storage than the input.
Only a CS0169 "field is never used" warning hints at it.
AutomaticProperties governs only whether trivial accessors collapse to
"get;"/"set;"; the declaration removal inside the transform is a separate step
that FieldKeyword alone is enough to justify. The entry gate now mirrors
CSharpDecompiler.MemberIsHidden, which already made the field's visibility
depend on either setting, with GetterOnlyAutomaticProperties vetoing the
getter-only case for both.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
HandleConditionalOperator collapses `if (c) a = x; else a = y;` into a
conditional operator, innermost first, and keeps going for as long as the
chain does. A source else-if ladder therefore comes back as one expression,
however long it was: the sample in #2027 decompiles to a single
2095-character statement, and one NLog method to 2230 characters nested 29
brackets deep.
ExpandNestedConditionals undoes that past one level, so a statement keeps at
most a single conditional operator.
It runs at the end of the pipeline rather than inside ExpressionTransforms,
because every transform that needs its input to be a single expression has
to see the collapsed form first: object and collection initializers, `with`,
switch expressions, interpolated string handlers, and the query lambdas the
C# stage later rewrites into clauses. Cutting the chain earlier leaves an
if-else between the statements they pattern-match on and they silently stop
matching - an object initializer assigning an init-only member then does not
even compile. The same reasoning ReduceNestingTransform gives for walking
back ConditionDetection's aggressive else-inlining once the structure is
settled.
A chain already stored to a variable is expanded into that variable, so
nothing has to be decided: the variable carries its own type. A chain in any
other position - an argument, a return value, a field store - has nothing to
expand into, and ILExtraction can give it one. The temporary ILExtraction
creates is typed from the stack type though, where `I4` is `int`, `bool`,
`char` and every enum at once, so extracting on that basis turned a bool
into `int num` with `if (num == 0)` and an enum into
`dbType = (IsFixedLength ? 22 : 0)`.
InferExpectedType is the counterpart to InferType that answers this: where
InferType asks what a value is, it asks what the position the value flows
into says it should be - a parameter, a return type, a field, all of which
carry their type in metadata. Extraction is done only where that question
has an answer, and the temporary is typed from it. The receiver of a call
then reads `XPathNavigator xPathNavigator`, not `object obj` with a cast
back, and a field store keeps its enum's member names.
The Pretty fixture covers what must NOT change: an array initializer, a
query lambda, a ref local, a switch expression, an object initializer with
an init-only member, a `with` expression, a catch-when filter and both
constructor-initializer forms. The positive case is an ILPretty test,
because a Pretty fixture is its own input and expected output, and a chain
that round-trips through collapse and expansion has no fixed point there.
The PdbGen test records the cost in breakpoints: the compiler's single
sequence point for the collapsed statement becomes one per expanded
statement, which is inherent to splitting a statement in two.
#2027
Assisted-by: Claude:claude-opus-5:Claude Code
A dynamic call site that names a type passes typeof(T) as its target. When
a later argument contains control flow, the compiler stores that typeof in
a temporary. ILInlining does not undo this: it inlines a store only into
the immediately following instruction, so an intervening statement leaves
the typeof behind, and the expression builder printed the temporary instead
of the type. Substituting the typeof back into the target slot is not an
option either, because a call there has side effects and blocks inlining of
the remaining arguments.
The type is therefore stored on the instruction. Object creation already
did this, but kept the field private, so the expression builder re-derived
the type from the target argument and failed on the spilled form. Member
invocation gets the same field. Both drop the target from Arguments, so the
dead-argument handling removes the store; ArgumentInfo keeps its entry for
the target, because the invocation symbol is built from it.
The type of an object creation is not nullable: the transform returns
before constructing the instruction when it cannot match the typeof, and
substitutes the unknown type otherwise. An unresolvable type therefore
reaches the expression builder as the unresolved type it is, and prints as
`?` like any other, rather than being indistinguishable from a missing one.
Those two are also the only binder method kinds that ever see
CSharpArgumentInfoFlags.IsStaticType. Every other way of naming a type as
the receiver binds statically and leaves only a conversion of the dynamic
operand behind.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Dock 12.1.0.6 removed the public JsonConverterFactoryList/JsonConverterList<T>
converters from Dock.Serializer.SystemTextJson that ILSpyDockJson used to
deserialize IList<T> into ObservableCollection<T>. Dock now does the same
substitution with an internal JsonTypeInfo modifier that swaps CreateObject
for IList<T> enumerables. ILSpyDockJson mirrors that technique in its own
modifier chain, which also removes the per-element JsonSerializer.Serialize
side effect the old converter had.
Also bumps Xaml.Behaviors.Avalonia, ProDataGrid, AwesomeAssertions, CliWrap,
NUnit3TestAdapter, and the decompiler minor version to 11.1.
Assisted-by: Claude:claude-fable-5:Claude Code
FindRefStructParameters dropped generic instantiations, so a parameter
typed 'ref <>c__DisplayClass0_0<T>' never reached RefStructTypes. Both
consumers therefore missed local functions whose declaring type or method
is generic: the signature test for an obfuscated local function, and
LocalFunctionNeedsAccessibilityChange, which left such a function internal
while its closure struct stayed private - the recompiled output then fails
with CS0051.
Cross-module signatures still drop out, because the generic type part of an
instantiation goes through GetTypeFromReference, which returns nil.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Whether an unresolvable type is a reference type is not a property of the
type but of the metadata that mentioned it: a signature spelling it
`valuetype T` yields false, a bare TypeRef yields null. UnknownType.Equals
compares the flag, so the two spellings of one missing type compared
unequal and EquivalentTypes reported false - the decompiler then emitted a
cast between a type and itself.
Erasing the flag in NormalizeTypeVisitor keeps the relaxation inside the
comparisons that ask for erasure, next to the nullability, modopt and tuple
erasure that are use-site spellings of the same kind. Dropping the term
from UnknownType.Equals instead was measured and rejected: Equals also keys
CSharpConversions' implicit-conversion cache, where merging the two
spellings lets whichever conversion is computed first answer for both,
adding 398 boxing casts across two real-world assemblies.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
This was due to StackType.O doing double-duty as `object` and `other`.
While ExpressionBuilder would often improve the type of such locals, the `object` nevertheless ended up used in a couple of places, e.g. via the `typeHint`. This could result in value types being boxed even though the original IL didn't contain any `box` instruction.
This is an attempt to use better types for stack slot variables created by ILReader. The idea is: there aren't many IL instructions that produce "other" value types, and `InferType()` already handles pretty much all of them, so we can use that to assign types to our stack slots.
It's a bit more tricky if the stack is pushed to on multiple branches that join together before the value is used: here the variable type must be suitable for both assignments. In this case, we go back to the previously-used stacktype.
Typing "M:System.Linq.Enumerable.Where" at a command line is a reasonable thing
to do, and it found nothing: resolution compares the whole id string, so a form
without the parameter list only ever matched a member that genuinely takes none.
Spelling the signature out is no answer, because it means knowing the overload
count before asking. The same goes for a generic arity - and the exact spelling,
Dictionary`2, does not even survive an unquoted bash prompt, where a backtick
starts command substitution.
None of that makes the short form legal. Measured against Roslyn: its own
DocumentationCommentId resolver accepts no abbreviation at all, and the compiler
never emits one - a cref is a different grammar, which the compiler binds and
rewrites into a full id, warning CS0419 and picking one member when the cref is
ambiguous. A prefixed cref is copied through unvalidated, so an id in a
documentation file can be anything a human typed.
So the id grammar stays exact and IdStringProvider stays with it, which is what
lets cref-following trust its answer. The tolerance belongs to the callers that
serve people typing, and lives in DocumentationIdSearch as a ladder that loosens
one thing at a time: the exact id, then the id without its parameter list, then
without generic arities. Stating a detail wrongly still finds nothing; only
leaving one out asks for any. A rung may match several members and all of them
are returned, because which to present is the caller's decision and hiding the
rest would hide that the id was ambiguous.
ilspycmd shows every member of the group, headed by a comment naming the
ambiguity, and accepts the shapes people actually type: no prefix, a shortened
namespace, and arity written the cref or C# way.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
This also matters in the `1 => DateTime.Now, 2 => null` case -- BestCommonType infers `DateTime` here, but we need `DateTime?` instead. But both had `StackType.O` so this went wrong prior to this commit.
* merge object/dynamic distinctions like we do with tuple element names. This fixes BestCommonType(object, dynamic).
* add a test that `new[] { 1, null }` has the "best common type" = `int`. The conversion error from `null` to `int` only happens later, it's not related to the best common type computation.
A Roslyn local function name is "<caller>g__name|x_y", where the trailing digits
are a synthetic disambiguator that SplitName has to strip before the scope-local
renumbering can run. An obfuscated name has no such suffix, so running it through
the same path renames "smethod_1" to "smethod_" -- a needless second mangling on
top of what the obfuscator already did.
#3202
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Obfuscators strip the CompilerGeneratedAttribute and rewrite the
"<caller>g__name|x_y" name, which is all IsLocalFunctionMethod had to go on.
The method then stays an ordinary static method, its display struct escapes by
ref into a plain call, and TransformDisplayClassUsage correctly refuses to
scalar-replace it -- so the closure fields leak into the output as
"<>c__DisplayClass29_0_.iid" (issue #3202).
The one marker an obfuscator cannot remove is the signature: Roslyn emits
struct closures exclusively for local functions, and no hand-written C# can
name a "<>c__DisplayClass" type, so a by-ref parameter of one identifies the
method regardless of what it is called.
#3202
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The file this branch adds takes the contributor's name rather than
AlphaSierraPapa, and three comments it added drop their en-GB spelling.
EndOpenGroups now requires its target depth: zero is the one value that closes
groups the caller does not own, which is the misattribution the depth argument
was added to prevent.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The state the ExpressionBuilder and StatementBuilder leave behind was only
reachable as "state before the first AST transform" - an entry that names a
transform rather than the state, and that sits below every member's group in a
tree with one group per member. It is now a top-level step at the seam, where
the whole type is converted and nothing has transformed it yet.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Two extra pieces of state existed to reconstruct what the stepper already
records: which member a halt belongs to. The step the limit stopped on answers
it, except on a member's opening step, which is where the previous member's
state ends - and there the last step actually recorded answers it instead.
IL group openers gain an anchor so their position resolves. The member opener
deliberately keeps none: anchoring it to the member the pipeline is about to
start is exactly the misattribution the fallback exists to avoid.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Recording only gated the IL half, so a run with it off still numbered the C# AST
transforms into the shared stepper. That gave one pipeline two numbering scales,
and a step index is only meaningful against the scale it was recorded on: a tree
captured under one and replayed under the other selects a different step. It
also let the crashed-member attribution fire on a counter that had never moved -
a limit of zero matched at every throwing transform and rendered an unrelated
member's ILAst.
The flag now gates both halves, so steps exist exactly when recording is on, and
it lives on the pane instance rather than a static the background decompile read
across threads.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
The pane used to split the pipeline across two languages: the ILAst language
stepped the IL transforms, the C# language stepped the AST transforms, and
nothing showed the seam between them, so a step index meant a different thing
depending on which language happened to be selected. Recording both halves into
one Stepper makes an index replayable across the whole pipeline; a limit that
lands in the IL phase has no C# to print, so the halted function is rendered as
ILAst instead.
Which function that is takes some care, because a member group's EndStep is the
next member's first step: a halt standing on a member's opening step belongs to
the member that just finished, a transform that throws where the limit was aimed
has to hand over the ILAst it half-transformed (what the ILAst language showed
as "ILAst after the crash"), and a step recorded on a helper function the
pipeline has not attached yet belongs to that function's own tree.
Retention stays opt-in twice over: the decompiler records IL steps only when
asked to, and the pane asks only while its view is on screen. Every kept step
pins the ILAst it captured, which for one type runs to tens of thousands of
nodes, so a closed pane would be paying for a tree nobody displays.
What is left of the ILAst language is its typed-IL dump, which runs no
transforms at all. That stays, as TypedILLanguage. IDebugStepProvider was down
to a single implementation and is removed.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Two test fixtures carried their own copy of the 32-byte signature, which
would silently drift from the real one. The signature is now an internal
member of SingleFileBundle and ILSpy.Tests gets internals access to the
decompiler assembly, matching what ILSpyX already grants it.
Assisted-by: Claude:claude-fable-5:Claude Code
IsBundle scanned up to but excluding the last position at which a full
signature fits, so a signature occupying the final 32 bytes of the region
was never compared. Windows hid this: a memory-mapped view there reports
the page-rounded region size, leaving trailing zero bytes after the file.
On Linux and macOS the view length is the exact file length, and the
LoadedPackage bundle tests, whose synthetic bundles end with the
signature, failed there with FromBundle returning null. Real bundles keep
apphost code after the signature, which is why this stayed latent.
Assisted-by: Claude:claude-fable-5:Claude Code
A .resources file's resource count, type count, name lengths, binary
resource lengths and serialized-object lengths all come from the file
and were only checked for being non-negative before sizing an allocation.
A crafted file can therefore request multi-gigabyte arrays from a
few-hundred-byte payload (CWE-789), turning a click on a resource node
into an out-of-memory condition. The serialization-format kind was
additionally an assert-only check that vanishes in Release builds.
Each element of these counts occupies at least one byte in the stream, so
a value needing more bytes than remain after the current position cannot
be honest. Reject it with the same BadImageFormatException the callers
already handle, and promote the format-kind assert into a real check.
Assisted-by: Claude:claude-fable-5:Claude Code
The JSON parser's value/object/array readers are mutually recursive with
no depth limit, so input nested tens of thousands of levels deep overflows
the stack with an uncatchable StackOverflowException (CWE-674) that kills
the process. This is reachable through DotNetCorePathFinder, which parses
the .deps.json shipped next to an opened assembly, so a crafted manifest
beside a target turns dependency resolution into a clean process kill.
Thread a depth counter through the readers and throw a catchable
JsonParseException once nesting passes a fixed cap. The cap (64) matches
the System.Text.Json default and is far beyond any real dependency graph.
Assisted-by: Claude:claude-fable-5:Claude Code
Making a conversion implicit by unwrapping it hands the operand to a
different target type, and a default literal takes its value from that
type: "S? x = new S?(default)" holds a value, while "S? x = default" is
null. Unwrapping the nullable constructor around a shortened literal
therefore turned "S? x = default(S)" into a null nullable. The literal is
spelled out again whenever unwrapping moves it to a type other than the one
it was shortened from.
Converting a using resource to the declared variable type is unconditional
now (except when the declaration says "var", which supplies no type): the
declaration always spells the type out, so any conversion to it may stay
implicit, which is also what shortens default(T) there.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
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
There's an additional local variable when decompiling the non-optimized code; and explicitly putting that variable
into the test case just makes it fail due to yet another additional variable.
An operand boxed for the GetAwaiter call is typed 'object', so the member
lookup that decides whether the await needs a cast finds nothing and a
redundant cast to the receiver type reaches the output. C# inserts that boxing
conversion implicitly, so the box may be dropped -- but only after the lookup
confirms the unboxed operand still binds the same GetAwaiter, and only via the
resolve result: UnwrapChild detaches the operand from the AST, so running it
speculatively leaves a cast with no child behind and decompilation of the whole
method falls back to the raw state machine.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
I think this isn't reliable enough yet to actually omit parameter types for lambdas (it only protects against switching to the wrong overload; not against type inference failures); so for now it's only used in the query expression transform.
The sign of a constant cannot decide whether to emit a unary minus: MinValue
and NegativeInfinity are negative, yet are their own members and must not be
negated. Deriving it that way emits -float.MinValue for float.MinValue, which
is a different value.
Which constants are reachable by negation is also not obvious: -MaxValue is
exactly MinValue and both infinities have their own members, so Epsilon is the
only one, but establishing that takes a proof rather than a read. Recording it
in the table states the invariant instead, and leaves the lookup itself as the
single dictionary probe it was before.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Siegfried Pammer
Daniel Grunwald
Christoph Wille
SychicBoy