Diagnostic Reference¶

Desi's diagnostics are single-sourced from a catalog (compiler/internal/diag/codes.json). Every error and warning has a unique code for easy lookup.

152 diagnostic codes across 17 categories.

Lexer Errors¶

Tokenization and lexical analysis

Code	Title	Help
`DLE0001`	unterminated string	did you forget a closing quote?
`DLE0002`	mixed tabs and spaces in indentation	use either spaces or tabs consistently; do not mix on the same line
`DLE0003`	spaces used for indentation; tabs required	Desi enforces tabs-only indentation. Configure your editor to insert tabs (not spaces) for leading whitespace.
`DLE0011`	invalid number literal
`DLE0012`	invalid float fraction	digits must appear after the decimal point; underscores cannot lead/trail or double
`DLE0013`	invalid float exponent	write like '1.2e+3'; exponent must contain digits (underscores allowed between digits)
`DLE0014`	invalid hex literal	hex digits are 0-9 or a-f (case-insensitive); underscores cannot lead/trail or double
`DLE0015`	invalid hex fraction	fractional part must contain hex digits
`DLE0016`	hex float missing exponent 'p'	hex floating-point literals require a 'p' exponent, e.g. 0x1.fp3
`DLE0017`	invalid hex float exponent	use 'p±', underscores only between digits
`DLE0018`	invalid binary literal	binary digits are 0 or 1; underscores cannot lead/trail or double
`DLE0019`	invalid octal literal	octal digits are 0..7; underscores cannot lead/trail or double
`DLE0020`	invalid escape sequence	supported: \ \" \n \r \t \0 \xNN \uXXXX \UXXXXXXXX
`DLE0099`	lexer error

Parser Errors¶

Syntax and grammar

Code	Title	Help
`DPE0001`	unexpected token	this token is not valid here; check for a missing delimiter or keyword before it
`DPE0002`	expected a different token	the parser expected a specific token here; verify punctuation and keywords
`DPE0003`	unclosed delimiter	a '(' '[' or '{' was opened but not closed on this path
`DPE0004`	trailing or extra token	remove extra punctuation or a stray comma at the end of the list
`DPE0005`	invalid assignment target	only names, tuple patterns, or index/field targets may appear on the left of an assignment
`DPE0100`	unexpected token after 'pub'
`DPE0101`	wildcard '_' cannot have a payload
`DPE0110`	missing 'let' before variable declaration	Write 'let name = …' to declare a variable; plain '=' is not a statement operator.
`DPE1001`	async only valid before 'def'	Place 'async' immediately before 'def', or remove it.
`DPE1002`	async not allowed before 'let'	async is not a statement modifier; remove it before 'let'.
`DPE1003`	await requires an expression	Write 'await ' where is a future.

Type Errors¶

Type checking and inference

Code	Title	Help
`DDF0005`	inconsistent default parameters across overloads	all overloads for a function name must agree on which parameters have defaults
`DTE0001`	undefined name	this name is not defined in the current scope
`DTE0002`	arity mismatch in grouped binding	the number of names on the left must equal the number of values on the right
`DTE0003`	name already defined in this scope	choose a different name or remove the earlier declaration
`DTE0004`	type mismatch	the expression does not have the expected type
`DTE0005`	return type mismatch	the returned expression does not match the function's declared return type
`DTE0006`	cannot assign to immutable variable	declare the variable with 'mut' if you intend to reassign it
`DTE0010`	symbol is not public	symbols imported from another module must be declared with 'pub'
`DTE0011`	public constant must be compile-time constant	public constants must be literal compile-time values
`DTE0012`	public let cannot be mutable	remove 'mut' from public top-level let declarations
`DTE0013`	mutation requires ':=' operator	use ':=' instead of '=' when mutating an existing value (e.g., obj.field := value)
`DTE0014`	use 'none' instead of 'void'	Desi does not have 'void'; use 'none' for no-value types
`DTE0020`	reserved keyword used as an identifier	choose a different name; language keywords and special names cannot be used as identifiers
`DTE0021`	cannot shadow prelude builtin	rename your binding; builtins like 'len' and 'print' cannot be redefined
`DTE0022`	name conflicts with imported symbol	rename your declaration; imported names cannot be redefined
`DTE0023`	'void' is not a type; use 'none'	Desi uses 'none' to denote no value. Replace 'void' with 'none'.
`DTE0030`	incompatible struct assignment	assign a value of the same struct type
`DTE0031`	unsupported assignment target	the left-hand side must be a name, index, or field expression
`DTE0032`	unknown struct type	this struct type is not defined
`DTE0033`	field access on non-struct	only struct values support field access
`DTE0034`	cannot assign to field on non-struct	the left-hand side must be a struct value
`DTE0035`	defer is not allowed here	move the 'defer' to the function top level
`DTE0036`	defer expects a call expression	use 'defer some_func(...)'
`DTE0037`	invalid condition type	conditions must be bool or int
`DTE0038`	symbol is not a value	call the function or refer to a constant/type as appropriate
`DTE0039`	unknown symbol in module alias	verify the symbol name exported by that module
`DTE0040`	unknown field on struct	check the field name against the struct definition
`DTE0041`	unknown enum variant	verify the variant name declared in the enum
`DTE0042`	duplicate match arm	each variant should appear at most once
`DTE0043`	payloadless variant used with a binder	remove the binder or use a variant that carries a payload
`DTE0044`	wrong number of arguments	constructors for payloadless variants take no arguments; payloadful ones take exactly one
`DTE0045`	wrong number of arguments	verify the arity of the function exported by that module
`DTE0046`	wrong number of arguments	pass exactly the required number of arguments
`DTE0047`	incompatible enum assignment	assign a value of the same enum type/variant
`DTE0050`	single-element tuples are not supported	use the value directly instead of wrapping it in a tuple; single-element tuples add no value
`DTE0051`	global variable must be immutable	Global variables cannot be mutable (no 'mut'). Use 'let NAME = ...'.
`DTE0052`	non-exhaustive match	add arms for the missing variants or a wildcard '_' arm
`DTE0101`	no matching overload	no overload matches the provided argument types
`DTE0102`	ambiguous overload	multiple overloads match the provided argument types
`DTE0103`	bad pipeline feed	pipeline requires a call on the right; the piped value becomes the first argument
`DTE0104`	invalid operand types	operator does not support these operand types
`DTE0105`	value is not callable	only functions can be called
`DTE0106`	cannot mix positional and named arguments in struct initialization	use either all positional arguments (by field order) or all named arguments; do not mix them
`DTE0107`	duplicate field in struct initialization	each field should be specified exactly once
`DTE0108`	unknown field in struct initialization	check the field name against the struct definition
`DTE0109`	missing field or wrong arity in struct initialization	provide all required fields — either by name or positionally in declaration order
`DTE0110`	argument is void	arguments must produce a value; remove expressions of kind 'none'
`DTE0111`	unsupported argument kind	convert the expression to a supported kind (int/float/str/bool)
`DTE0112`	wrong number of arguments	check the function's signature and adjust the number of arguments
`DTE0113`	cannot infer type parameter	state it explicitly with turbofish, e.g. Stack::(), or annotate the binding
`DTE0114`	wrong number of type arguments	pass one type argument per type parameter, or omit them to let Desi infer
`DTE0130`	'break' or 'continue' outside a loop	these only apply to the innermost enclosing 'for' or 'while' body
`DTE0131`	wrong type for an index or key	lists and strings are indexed by int; a dict key must match the declared key type; a tuple index must be an integer literal
`DTE0132`	builtin is only valid as a for-loop iterable	enumerate(), reversed() and zip() are loop syntax, not values — write 'for x in reversed(items):'. Unlike range(), they cannot be bound to a variable or used in a comprehension
`DTE0200`	missing stdlib import	stdlib modules must be imported before use; add 'import ' at the top of your file
`DTE1001`	`await` is only valid inside async functions	Mark the function `async`, or remove `await`.
`DTE1002`	cannot await a non-future value	Only values of kind `future<T>` can be awaited.

Module Errors¶

Imports, resolution, and module system

Code	Title	Help
`DME0001`	import cycle	break the cycle by removing or refactoring one of the imports
`DME0002`	cannot find module	verify the dotted path and ensure the file exists under a search root (project dir or compiler/lib)
`DME0003`	name is not exported by that module	check the spelling, and mark the declaration 'pub' in the module that defines it
`DME0004`	failed to read file	Check file permissions and path casing.
`DME0005`	parse failed during resolution	Fix parser errors in the imported file.
`DME0006`	bad entry path	Pass a valid .desi file; avoid directories or missing paths.
`DME0007`	entry not found	Make sure the entry file exists and isn’t a directory.
`DME0008`	circular import detected	Circular imports are not allowed. Refactor to break the dependency cycle.
`DME0009`	reserved namespace	'std' is reserved for the standard library. Rename your module.
`DME0010`	module shadows stdlib	Local module shadows a stdlib module. Rename it or use 'from std.X import ...' for stdlib.
`DME0011`	ambiguous module	Both a file (X.desi) and package (X/__mod.desi) exist. Remove one to resolve ambiguity.
`DME0099`	internal error	This indicates a compiler bug; please report with a repro.
`DMW0001`	duplicate import	remove the repeated import; importing the same module multiple times has no effect
`DMW0002`	module imports itself	Remove the self import; a module can reference its own symbols directly.
`DMW0003`	import alias conflict	Give different aliases (e.g., 'import foo as f1') or adjust 'from' items to avoid local name collisions.
`DMW0004`	unused import	Remove the import or reference a symbol from it.
`DMW0005`	unused imported name	Remove the unused item from the 'from' list.

Borrow Errors¶

Move semantics and borrow checking

Code	Title	Help
`DBR0001`	cannot hold 'inout' borrow across 'await'	Move the 'await' earlier or avoid 'inout' in async callees. Phase-2 will refine this with data-flow for narrower borr...
`DBR0002`	inout argument must be a mutable lvalue	Pass a mutable lvalue such as an identifier, field access, or index expression.
`DBR0003`	inout cannot alias with other arguments	Pass distinct base variables/receivers, or avoid combining inout with ref to the same base in a single call.
`DBR0004`	use after move	Bind to a new name or avoid moving the value before using it again.
`DBR0005`	ref argument must be an lvalue	Pass an lvalue such as an identifier, field access, or index expression.

Concurrency Errors¶

Guards, arenas, and structured concurrency

Code	Title	Help
`DSY0001`	TaskGroup must be used with 'using' guard	TaskGroup requires RAII for proper cleanup. Use 'using tg = sync.TaskGroup():' to ensure resources are freed.
`DSY0002`	Sender should be used with 'using' guard	Consider using 'using tx = ch.sender():' to ensure the sender is properly dropped.
`DSY0003`	Receiver should be used with 'using' guard	Consider using 'using rx = ch.receiver():' to ensure the receiver is properly dropped.
`DSY0004`	ReadGuard should be used with 'using' guard	Consider using 'using guard = rw.read():' to ensure the read lock is properly released.
`DSY0005`	WriteGuard should be used with 'using' guard	Consider using 'using guard = rw.write():' to ensure the write lock is properly released.
`DSY0010`	type does not satisfy trait bound	The type argument does not implement the required trait. Ensure the type implements the trait or use a compatible type.

Class Errors¶

Classes, inheritance, and dunder methods

Code	Title	Help
`DCL0001`	dunder method must be pub	All dunder methods (new, repr, eq, close, etc.) must be declared with 'pub'.
`DCL0002`	base must be a class	Inheritance requires a class type; structs and other types cannot be used as base classes.
`DCL0003`	invalid close signature	close must have signature: close(self) -> none
`DCL0004`	cannot assign to immutable field	declare the field as 'pub mut field: Type' to allow mutation
`DTC0020`	del must have zero parameters	del is a destructor and takes only 'self' (no other parameters)
`DTC0021`	del must not have a return type	del is a destructor and must return void (no return type annotation)

Call Errors¶

Function calls, defaults, and named arguments

Code	Title	Help
`DCA0001`	unknown named argument	the provided argument name does not match any parameter in the selected overload
`DCA0002`	duplicate named argument	remove one of the occurrences or rename the argument
`DCA0003`	positional argument after named arguments	once a named argument is used, all subsequent arguments must be named
`DDF0001`	default value must be a compile-time constant	use a literal or other compile-time constant expression as the default value.
`DDF0002`	inout parameters cannot have default values	remove the default value or change the parameter mode; inout parameters cannot have defaults.
`DDF0003`	parameters with defaults must come last	once a parameter has a default value, all following parameters must also have defaults.
`DDF0004`	default parameters must be consistent across overloads	overloads of the same function must agree on which parameters have defaults.

Collection Errors¶

Lists, dicts, sets, and other containers

Code	Title	Help
`DCO0001`	type has no length	len(x) is defined for strings (and, in M10, for list/dict/set/tuple). Use a supported type or convert appropriately.
`DCO0002`	unsupported membership	The 'in' operator is defined for strings (substring membership) in this phase. In M10, it will also support list/set ...

Numeric Errors¶

Numeric types and overflow

Code	Title	Help
`DNT0001`	mismatched numeric widths	Use the same-sized types or convert explicitly; mixing widths is not allowed yet.
`DNT0002`	signed/unsigned mismatch	Use matching signedness or convert explicitly; implicit signed/unsigned mixing is not allowed.

FFI Errors¶

Foreign function interface

Code	Title	Help
`DFI0001`	invalid @extern decorator arguments	Use @extern("C"[, "lib"]). The first argument must be a string specifying the ABI; an optional second string may spec...
`DFI0002`	@extern only allowed on public functions	Place @extern on 'pub def' so external users can link against it.
`DFI0003`	extern call in safe context	Calls to @extern functions must occur inside an 'unsafe:' block.
`DFI0004`	non-FFI-compatible field type in @ffi_struct	@ffi_struct fields must use FFI-compatible types: int, i8-i64, u8-u64, float, f32, f64, bool, cptr, or other @ffi_str...
`DFI0005`	@ffi_struct cannot be generic	C-compatible structs cannot have type parameters. Remove the generic parameters.
`DFI0006`	out parameter not found in function signature	Each name in out=[...] must match a parameter of the safe extern function. Check spelling or remove the invalid entry.

Prelude Errors¶

Built-in functions and prelude

Code	Title	Help
`DPL0001`	cannot shadow builtin	builtins like print, len, str, and bool are always available; use a different name.

Project Errors¶

desi.mod and project configuration

Code	Title	Help
`DPM0001`	invalid key/section in manifest
`DPM0002`	invalid value type in manifest
`DPM0003`	missing entry point in manifest
`DPM0004`	invalid or non-existent root directory
`DPM0005`	invalid diagnostics value
`DPM0006`	entry file not found
`DPM9999`	manifest I/O error

Warnings¶

Non-fatal issues and code quality

Code	Title	Help
`DW0001`	unused variable or parameter	Prefix the name with '_' to silence this warning.
`DW0002`	name shadows an outer binding	consider renaming to avoid confusion
`DW0004`	unreachable code: statement after return
`DW0006`	function may fall through without an explicit return
`DW0008`	global constant should be UPPER_CASE	follow the naming convention: use UPPER_CASE for global constants (e.g., MY_CONST)

Performance Lints¶

Patterns with a complexity cost, reported as warnings

Code	Title	Help
`DPR0001`	deeply nested loop (O(n²) or worse)	Consider restructuring with hash maps, sorting, or reducing nesting depth.
`DPR0002`	string concatenation inside loop	String '+' in a loop creates O(n²) allocations. Use a list and join, or a string builder.
`DPR0003`	repeated collection lookup with same key	Cache the result in a local variable instead of looking up the same key multiple times.
`DPR0004`	unbounded allocation inside loop	Creating new collections inside a loop body may cause excessive allocations. Pre-allocate or move outside the loop.

ORM Errors¶

Model and query definitions

Code	Title	Help
`DORM0001`	unknown ORM field	The field name does not match any field registered in a db.model() definition. Check for typos in the field name.

Formatter Errors¶

desifmt safety check

Code	Title	Help
`DFM0001`	formatting would change the code	The formatter only rearranges layout, so it verifies that its output still lexes to the same tokens as the input. It did not here, so the file was left untouched rather than written over with something different. This is a formatter bug — please report the file.