Appendix B — Diagnostics index

The first two tables list the diagnostics this book’s examples actually trigger. Diagnostics you can meet but the examples do not show are gathered at the end under “Other diagnostics”. A code keeps its meaning across releases; the compiler explains the details and the repair at the site (--diag-json in a machine-readable form).

At translation time#

Code	Meaning	Shown in
E-ACCESS-MODE	the body breaks the read or write promise made with access	chapter 27
E-ACTOR-FIELD	an actor’s state field is read from outside	chapter 25
E-ACTOR-STATE-REF	a borrow is kept in an actor state field	chapter 25
E-ACTOR-UNINIT	a just-spawned actor’s slice state field is read before it is set	chapter 20
E-ALLOC-AMBIGUOUS	more than one fitting allocator and none chosen with using	chapter 20
E-ALLOC-NESTED	allocated from an outer source while an inner region of the same root is open	chapter 18
E-ALLOC-NOCAP	declares alloc but receives no allocation capability	chapter 16
E-ALLOC-NOSOURCE	a call draws from an allocator but no fitting one is visible in this op	chapter 20
E-ALLOC-OUTLIVES	region bytes handed to an actor born outside the region	chapter 18
E-ALLOC-SHARED	an allocator whose cursor is not atomic is handed to a task	chapter 26
E-ALLOC-TASK	an op that carves from a root is spawned as a task	chapter 26
E-ALLOC-USING-UNUSED	using on a call that does not draw from an allocator	chapter 20, chapter 34
E-ASM-TARGET-UNKNOWN	the machine name in an asm clause is not a known target	chapter 30
E-ASM-UNBOUND	the assembly template names an undeclared operand	chapter 30
E-ATOMIC-NOCAP	declares atomic but receives no cap atomic	chapter 27
E-ATOMIC-ORDER	a memory ordering that has no meaning for that atomic operation	chapter 27
E-BLOCK-UNCLOSED	a block opened with do is never closed with end	chapter 2
E-BOUND-UNSAT	the type argument does not satisfy the required trait	chapter 22, chapter 23
E-BRAND-REUSED	a brand opens a second storage	chapter 35
E-CAP-FORGE	spawns an actor holding a capability without holding that capability	chapter 16, chapter 20, chapter 25
E-CAP-KIND	a capability of the wrong kind was handed over	chapter 16
E-CAP-LOCAL	a received capability was copied into a local name	chapter 16
E-CAP-MISSING	a capability-requiring builtin was not given its capability as the first operand	chapter 16
E-CHAR	a character (symbol) this language does not have	chapter 6, chapter 7, chapter 8, chapter 9
E-CHAR-WIDTH	a character literal is not a single character	chapter 3
E-CLAUSE-ORDER	the clauses of an op header are out of the fixed order	chapter 2, chapter 3, chapter 22
E-COMPTIME-ARG	a run-time value in a comptime position	chapter 22
E-CONC-ALONE	a task group spawns one task that waits for a peer	chapter 26
E-CONC-DEADLOCK	every task in the group receives and none sends	chapter 26
E-CONFIG-TYPE	the configuration gives a value the option does not offer	chapter 31
E-CONFIG-UNDEF	a configuration or config names an undeclared build option	chapter 31
E-CONTRACT-DEAD	declares an error that requires already excludes	chapter 14
E-CONTRACT-IMPOSSIBLE	a call with constant arguments breaks the callee’s requires	chapter 14, chapter 35
E-CONTRACT-UNSAT	two preconditions that cannot both hold	chapter 14
E-DEP-MISSING	the file at a use … from place cannot be read	chapter 21
E-EFFECT	performs an effect its effects clause does not declare	chapter 15, chapter 20, chapter 26
E-EFFECT-CALC	a pure fn performs an effect	chapter 1, chapter 5, chapter 15, chapter 16, chapter 18, chapter 24
E-EFFECT-DUP	the same atom twice in an effects clause	chapter 15, chapter 44
E-EFFECT-NO-CAP	declares io (or similar) without a capability that authorises it	chapter 2, chapter 16
E-EFFECT-NONE-MIX	none written together with a real effect	chapter 15
E-EFFECT-PURITY	a fn writes state visible to its caller or actor	chapter 5, chapter 15, chapter 25
E-EFFECT-REDUNDANT	effects none written on a fn	chapter 5
E-EFFECT-UNDEF	an effect word outside the closed vocabulary	chapter 15, chapter 44
E-ENS-UNDEF	ensures names something undefined — the returned value is ret	chapter 14
E-ENTRY-PARAMS	the entry point takes a non-capability input	chapter 16
E-ENUM-DOT	an enum variant not closed with .	chapter 10
E-ENUM-INFINITE	a variant embeds its own type by value	chapter 10
E-ERR-UNDECLARED	returns an error not in its errors clause	chapter 11
E-ERRORS-STATE	an errors condition reads an actor state field	chapter 25
E-ESCAPE	a reference to a local escapes the op	chapter 12
E-EXCL	overlapping borrows or owner access to the same value	chapter 12, chapter 20, chapter 26, chapter 43
E-EXPR-APP	a call inside an expr island is not parenthesised	chapter 8
E-EXPR-CHAIN	comparisons chained in an expr island	chapter 3
E-EXPR-UNARY	a unary operator in an expr island	chapter 8
E-FFI-LINK	an extern op does not name the C symbol it calls	chapter 29
E-FFI-NOCAP	calls C without receiving cap c	chapter 29
E-FFI-NOEFFECT	an op calling C declares no effect	chapter 29
E-FFI-NOUNSAFE	calls C without the unsafe mark	chapter 29
E-FFI-TYPE	a type the C ABI cannot express crosses the boundary	chapter 29
E-FIELD-GLUED	tried to read a field by gluing a dot to a value — write field	chapter 3
E-FN-CAP	an op to be passed as a callback requires a capability	chapter 29
E-FN-NOTEXPORT	unsafe_fn names an op that is not export extern	chapter 29
E-FOLD-OP	a pipe stage names an op that does not exist	chapter 24
E-FOLD-ORDER	a fold stage op declares its accumulator with a type other than its result	chapter 24
E-GROUP-UNCLOSED	an unclosed parenthesis	chapter 3
E-GUARD-FALLTHROUGH	the else of a guard does not leave	chapter 7
E-HEAP-NOHOST	asks for the growing root on a freestanding target	chapter 18
E-IF-VALUE	if used as a value	chapter 6
E-IMMUTABLE	set on a name bound with let	chapter 6
E-IR-ARITY	an op is called with the wrong number of arguments	chapter 5, chapter 48
E-IR-UNDEF	a name unknown at that place	chapter 6, chapter 7, chapter 21, chapter 22, chapter 25
E-ISR-CALLED	an interrupt handler called from code	chapter 30
E-ISR-EFFECT	an interrupt handler does not declare effects device	chapter 30
E-ISR-PARAMS	an interrupt handler takes parameters	chapter 30
E-LET-NOVALUE	nothing after be	chapter 6
E-LOCK-NOTYET	shared lock types are not built yet	chapter 26
E-MATCH-INEXHAUSTIVE	a match does not cover every case	chapter 7, chapter 10
E-MATCH-REDUNDANT	a match arm can never run (an arm after _, overlapping ranges)	chapter 11
E-METHOD-RECV	an attached op’s receiver is not its first input	chapter 23
E-METHOD-UNDEF	no op of that name is attached to the receiver’s type	chapter 22, chapter 23
E-MMIO-BYVALUE	an mmio register block taken by value	chapter 30
E-MMIO-PERM	writes a read-only register	chapter 30
E-MONO-NOTYPE	a generic call gives no leading type argument	chapter 22
E-MREF-SLICE	mut ref slice used	chapter 12
E-NAME-BUILTIN	a builtin op’s name is used for a declaration or local	chapter 5, chapter 6
E-NAME-DUP	the same name declared twice in one module	chapter 21
E-NAME-SCOPE	a name declared inside a block is read outside it	chapter 6
E-NAME-SHADOW	re-binds a live name (shadowing)	chapter 3, chapter 6
E-OPT-UNUSED	a declared build option that no code reads	chapter 31
E-OWN-INCOMPLETE	a value that needs completion is dropped implicitly	chapter 19, chapter 28, chapter 36
E-OWN-JOIN	ownership state differs between branches	chapter 19
E-OWN-MOVED	uses a value after it was moved	chapter 19, chapter 25, chapter 28, chapter 35, chapter 36
E-PAR-ASSOC	the reduction operator is not associative	chapter 27
E-PAR-CARRY	a split loop writes a local that lives across iterations	chapter 27
E-PAR-FLOAT	a floating-point accumulation declared splittable	chapter 27
E-PAR-IDENTITY	a reduce starts from a value that is not the operator’s identity	chapter 27
E-PAR-NOLOOP	the parallel clause finds no loop to split	chapter 27
E-PAR-READ	a split loop reads another iteration’s element	chapter 27
E-PAR-WRITE	a split loop writes another iteration’s element	chapter 27, chapter 45
E-PIPE-NO-TERMINAL	a stage after the terminal	chapter 24
E-PIPE-STAGE	a word that is not a pipe stage	chapter 24
E-PROFILE-LEVEL	uses concurrency the build profile does not provide	chapter 25
E-REGION-ESCAPE	carries region bytes out of the region	chapter 18
E-RETURN-PARTIAL	some path does not return a value	chapter 3, chapter 5, chapter 7
E-SPAWN-SCOPE	spawns a task outside a task_group	chapter 26
E-STMT-ELSE	else sits inside the block	chapter 7
E-TIER-EFFECT	an effect the declared machine tier cannot carry	chapter 30
E-TOPLEVEL	something that cannot appear at top level is at top level	chapter 3
E-TRAIT-EFFECT	the implementing op has more effects than the signature	chapter 23
E-TRAIT-MISSING	an op required by the trait is missing	chapter 23
E-TRAIT-SIG	fn/proc in a signature, or a parameter-count mismatch	chapter 23
E-TRY-NORESULT	try used in an op that cannot return that error	chapter 11
E-TYPE-ARG	an argument’s type does not match the parameter	chapter 12
E-TYPE-ARGMUT	a read-only value is passed where it would be written (mut_ref of a let)	chapter 9, chapter 12
E-TYPE-ARRAY	array length written after the type	chapter 9
E-TYPE-BITCAST	bit_cast target is not a plain scalar	chapter 20
E-TYPE-COLLECT	collect into would put a wider value into a narrower buffer	chapter 24
E-TYPE-COND	a non-boolean in a condition	chapter 4
E-TYPE-DECL	be in a type declaration	chapter 13
E-TYPE-FIELD	a field is missing or unknown when building a struct	chapter 10
E-TYPE-INSTANCE	mixes different instances of the same generic	chapter 35
E-TYPE-KIND	a type of the wrong kind for that operation (e.g. cast of bool)	chapter 8, chapter 10, chapter 13
E-TYPE-MIX	float and integer literals mixed in one calculation	chapter 4
E-TYPE-MUT	writes an element of a non-mut slice	chapter 9
E-TYPE-NOMINAL	mixes nominally distinct types	chapter 13
E-TYPE-REF	writes through a shared ref	chapter 12
E-TYPE-REFVAL	a reference is used as if it were a value	chapter 12
E-TYPE-RETURN	the returned value does not match the op’s output type	chapter 11, chapter 31
E-TYPE-SIGN	mixes signs with no value-preserving widening	chapter 4, chapter 39, chapter 40
E-TYPE-WIDTH	the value does not fit the declared type	chapter 3, chapter 4, chapter 13
E-UNSAFE-UNDECLARED	declares the unsafe effect but the op is not marked unsafe	chapter 29
E-VEC-SPLAT	splat was written inline in an expression	chapter 27
E-VISIBILITY	reaches a non-exported name of another module	chapter 21
E-VOCAB-REMOVED	a removed word or spelling	chapter 3, chapter 5, chapter 7, chapter 15, chapter 48
E-WIDEN-SIGN	widen from a signed to an unsigned type	chapter 13
W-EFFECT-OVER	an effect declared but never performed (warning)	chapter 15, chapter 16
W-EXPORT-HIDDEN	an exported signature names a type the module keeps to itself	chapter 21
W-NOT-YET	a word accepted by name that has no meaning yet	chapter 13
W-USE-EXTERNAL	imports a module not in the compilation unit (warning)	chapter 32

Table 50.1 — Diagnostics shown by the examples

When execution stops#

Code	Meaning	Shown in
E-VM-OVERFLOW	integer overflow at the declared width	chapter 4
E-VM-DIV0	division by zero	chapter 4
E-VM-CAST	a narrowing or cast value does not fit	chapter 4
E-VM-SHIFT	shift amount not smaller than the width	chapter 4
E-VM-BOUNDS	index out of bounds	chapter 9
E-VM-NONE	took the value out of none	chapter 11
E-VM-CONTRACT	a contract was broken	chapter 14
E-VM-PANIC	the program called panic	chapter 7
E-VM-ANALYSIS	an eliminated check was actually needed (compiler bug)	chapter 40
E-TEST-FAIL	an expect in a test is false	chapter 31

Table 50.2 — Run-time diagnostics

Other diagnostics#

These do not appear in the examples but can come up. Most are stops by the VM (the executor) when running with --run. The VM exists for tests and cross-checking, so it holds its resources at fixed sizes, and past a limit it stops rather than quietly giving a wrong value. A limit is the VM’s size, not a defect of the program — the same program built natively usually runs fine.

code	meaning and repair
E-IR-EXTRA	operands are left over after an expr island — an island ends with one expression. Group with parentheses or split the line
E-IR-LIMIT	a compilation unit has more ops than the tool can carry — split the module
E-IR-LOCALS	one op has too many local names — split the op
E-MONO-FIXPOINT	generic monomorphisation does not finish (the type keeps growing) — break a generic that calls itself at a bigger type
W-COL0	a top-level declaration does not start at column 0 — the line may have ended up in the previous declaration’s body
W-UNBOUND	a named contract is declared but no op names it with satisfies
W-RFC-PENDING	a feature whose design is still at the RFC stage was used — nothing in the program to fix
W-CBE-SLOW	this op is lowered to the slow path (tagged values) in native code — --why-slow says why, op by op

Table 50.3 — At translation time — not in the examples

code	meaning and repair
E-VM-ERR	ok_value was taken from a result that is an error — ask is_ok first or pass it on with try
E-VM-DANGLING	a borrowed reference was used after the place it borrowed from ended (use after return)
E-VM-EXCL	a writing borrow of a place overlapped another borrow — end the first borrow before taking the next
E-VM-READONLY	wrote through a read-only reference (ref) — borrow with mut_ref to write
E-VM-FIELD	read a field that the record or register block does not have
E-VM-AWAIT	await was given something that is not a job handle — handles come from spawn <op>
E-VM-CHAN-EMPTY · E-VM-CHAN-FULL	received from an empty channel or sent to a full one with no scheduler to wait — a wait that can never end
E-VM-SCHED-LOOP	handlers keep sending each other messages, so the scheduler cannot settle
E-VM-FD · E-VM-FMODE · E-VM-FWHENCE	a file number that cannot be written (only 1 · 2) · an unknown open mode (0 · 1 · 2) · an unknown seek origin (0 · 1 · 2)
E-VM-FHANDLE · E-VM-SHANDLE · E-VM-REACTOR	the value passed is not an open file / socket / reactor handle
E-VM-EXTERN	an extern op whose body is in C was called in the VM — build natively to run it
E-VM-MMIO · E-VM-RESERVE	a register block at an absolute address / storage handed over by the linker was opened in the VM — they mean something only on the real machine

Table 50.4 — At run time — a mistake in the program

code	what filled up
E-VM-STACK · E-VM-DEPTH · E-VM-OOM	the operand stack · the call depth · memory to grow the call stack — recursion is too deep
E-VM-BOXPOOL · E-VM-RECPOOL · E-VM-STKPOOL · E-VM-BSETPOOL	the pools for values wrapped by some·ok · struct values · stack containers · bitsets — keep fewer values alive at once
E-VM-CHAN · E-VM-MBOX	64 channels · 4096 async mailbox slots — they are not reused, so one run makes at most that many
E-VM-FILEPOOL · E-VM-SOCKPOOL	how many files · sockets can be open at once — close the ones you are done with
E-VM-CHAIN-LIMIT	VM activations nested inside VM activations went too deep
E-VM-BUDGET	the step budget of a cross-checking (oracle) run ran out — it does not happen in a normal --run

Table 50.5 — At run time — a VM limit (not a defect of the program)