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A defn named after a builtin now wins, and says so once

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The author's rule: "allow shadowing but warn". A user (defn get ...) is
legal, the user's definition wins at every call site in the file that wrote
it, and the compiler warns once at the definition.

Builtin-wins was never a rule anybody wrote: named_call is one match on the
name, the builtin arms are string literals, and the three arms that look a
name up are the last three in it. So a guard goes first, the trailing three
are factored into ordinary_call, and both routes into it resolve a name the
same way.

The shadow stops at the file that declared it. An imported package's names
were qualified at the import, so a get written inside one is the builtin's
and stays the builtin's; the prelude is excluded by its file for the same
reason. programs/shadow-builtin.flan is both halves at once.

The warning prints from build_program, which is what every command and the
dev daemon's reload go through, in the shape --warn-memory established:
file:line:col, the squiggle, and an exit status that does not move.

And the message that described the old world is gone — the builtin-arity
note said a defn does not replace a builtin, which is no longer true and is
no longer reachable.
This commit is contained in:
Joseph Ferano 2026-09-20 19:28:00 +07:00
parent b87ae11fa8
commit e03028819c
8 changed files with 354 additions and 64 deletions
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129
FIX.org
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@ -2042,6 +2042,11 @@ wins every call and the definition is still unreachable; what changed is that
the arity message says so and notes the definition. Refusing the shadowing is
a language decision and was left to the author.
[Superseded the same day by the author's decision — see "Shadowing a builtin"
below. The builtin no longer wins, the definition is no longer unreachable,
and the arity note this paragraph describes has been removed along with the
world it described.]
* ~int~ and ~float~ as builtin aliases, 2026-09-20
The author, on the foreign-spelling list the diagnostics pass had just
@ -2098,8 +2103,12 @@ was a builtin. The rule is decided by the target, at registration:
- Anything else — refused: "int is a builtin alias for i32 and cannot be
redefined as i64 — delete this defalias, or give the type another name".
The alternative was the ~arity~ precedent, where the builtin wins and a note
surfaces at the error the shadowing caused. It does not transfer: a
The alternative was the ~arity~ precedent, where the builtin won and a note
surfaced at the error the shadowing caused — a precedent deleted later the
same day, when shadowing a builtin became legal and the user's definition
started winning instead (see "Shadowing a builtin" below); the reasoning
below stands either way, because neither world has anywhere to put the note.
It does not transfer: a
~(defalias int i64)~ has no later error site to hang a note on. ~resolve_name~
reaches ~ikind_of_name~ before the alias table, so the declaration would be
read as ~i32~ at every use and nothing would ever say so. Silence was the one
@ -2442,3 +2451,119 @@ failures were that row and the sixth was ~dev-trap-free-all~, so what is racy
is ~trap_park~ itself and every row that calls it — which is exactly what the
mechanism described there predicts. Per the sweep policy the ~@x86~ and
~@sanitize~ sweeps were not run here.
* Shadowing a builtin, 2026-09-20
The author's decision, in the author's words:
#+begin_quote
"allow shadowing but warn" — a user ~(defn get ...)~ colliding with a builtin
is legal, the USER'S definition wins at call sites (real shadowing, Clojure's
model: the def takes over, a warning says so), and the compiler warns once at
the definition site.
#+end_quote
** Where builtin-wins actually lived
Not in a table and not in a precedence list. ~named_call~ is one
~match name with~ whose arms are the builtin names written out as string
literals, and the three arms that look anything up — a local of ~Fn~ type,
~gsigs~, then ~env.fns~ — are the last three in that match. So a builtin won
because OCaml tried its arm first, and for no other reason. ~env.fns~ never
outranked anything; it was simply never reached for a name spelled like a
builtin. The old comment above ~arity~ said this outright ("the dispatch
above reaches every builtin arm before it ever looks in [fns]") and is the
only place it was written down.
** The resolution change
One guard, first arm of ~named_call~:
: | _ when shadows_builtin ctx loc name -> ordinary_call ctx ~want loc name args
and the three trailing arms factored into ~ordinary_call~ so that both routes
— falling past every builtin, and being sent straight there by the guard —
resolve a name by exactly the same rules. Order is now total and reads the
way a reader would guess: local of function type, then generic signature,
then the function table, then the builtins, then the struct and the
did-you-mean refusals.
~shadows_builtin~ asks three questions, cheapest first: is the name defined
(the two tables and the scope), is it a builtin's (otherwise there is no
order to change, and the enum/type-variable/machine-type cast arms keep
theirs), and is the definition visible here.
** The warning, verbatim
: shadow-builtin.flan:20:7: warning: get shadows the builtin get — every call in this program now reaches your definition
: 20 | (defn get [p P] i32 (.x p))
: | ~~~
Rendered by ~Loc.entry ~mark:'~' ~label:"warning: "~, which is the
~--warn-memory~ precedent, so flycheck parses it exactly as it parses an
error. Nothing raises and the exit status does not move. Unlike
~--warn-memory~ it is behind no flag: there is nothing to tune, and the line
is one line and rare.
It is printed from ~Check.build_program~ rather than from ~bin/main.ml~
beside ~print_memory_warnings~, because every route into the compiler passes
through that function — build, check, run, and the dev daemon's reload, which
is where a defn is most likely to be written. The list itself is
~Check.shadowed_builtins~, a pure function over the declarations, which is
what the tests ask.
** Scope, settled from the code
*Package-wide or program-wide: neither, and the mechanism already decided
it.* ~Load~ qualifies every name an imported package declares to ~alias/name~,
including its own uses of them, so a package's ~get~ is ~rl/get~ and cannot
collide with a builtin at all. What is left is the other direction: a program
that defines ~get~ and imports a package whose body calls the builtin ~get~.
That call must keep meaning the builtin, and it does — ~shadows_builtin~
answers false when the enclosing function's name is qualified, which inside
an imported package is always. The prelude is excluded the same way, by its
file: it is the language's own source and means the builtin wherever it
writes one. ~programs/shadow-builtin.flan~ is both halves in one program: 7
is the program's own one-argument ~(get p)~, 4 is the builtin ~get~ called
inside the package it imports.
*Prelude macros.* No rule was needed: the namespace is already one.
~(defn comment [x i32] i32 ...)~ against the prelude's ~(defmacro comment
...)~ is refused today as "comment is defined twice", with a note at the
prelude's definition, and the same for ~inc~ and ~dec~. Shadowing a builtin
is a different question precisely because a builtin is not a declaration —
it is an arm in the compiler, with nothing for a redefinition check to point
at. Macros expand before checking and key on the head name unconditionally,
so if the redefinition check were ever relaxed the macro would win and the
defn would be unreachable; that is not a state this compiler can reach, and
nothing was written to handle it.
*The one place the rule is conservative.* A bare REPL expression evaluated
with no file behind it (origin ~<eval>~) is checked with an unqualified
owner and so does shadow, which is right; a call written inside an imported
package's *global initialiser* — no enclosing function, so no qualified owner
— would not be excluded. Nothing in the corpus does that, and the fix if it
ever matters is to carry the package's file rather than the owner's name.
** Pins
- ~test_flan.ml~: the warning's kind, line and column; its message, matched
whole and not by needle; that it carries no notes; that the source which
used to be refused now checks; and that a program shadowing nothing warns
not at all.
- ~test_acceptance.ml~: ~programs/shadow-builtin.flan~ outputs ~7\n4\n~, and
the ~@x86~ sweep compares both backends over the same file.
- Removed: the ~check/builtin-arity~ kind, its message ("this is the builtin
get, which a defn of the same name does not replace"), its note ("is also
defined here, and this call is not reaching it — rename it to call it"),
and the three checks that pinned them. The situation cannot arise: the call
reaches the user's defn, whose arity is whatever it declared.
- Changed: the builtin-arm/~Check.builtins~ cross-check reads ~named_call~'s
source down to ~ | _ ->~ rather than ~ | _~, because the new first arm is
guarded and stopping at it read the whole region as empty.
** One thing the new package cost
A package under ~test/programs/pkgs/~ needs a ~glob_files~ line of its own in
four places in ~test/dune~ — the test stanza and the ~@valgrind~, ~@x86~ and
~@js~ sweeps — because dune's glob does not descend and the sweeps walk
~programs/*.flan~ whole. Without it the corpus row fails with "no package
at ..." and prints no FAIL line, only "1 failure(s)" at the end of the log:
worth knowing, because a grep for FAIL says green over it.
** What was run
~dune test --root .~ in the lane's worktree, forced: exit 0.
The heavy sweeps (~@x86~, ~@sanitize~, ~@valgrind~) were left to the batch.

2
docs/DIAGNOSTICS-AUDIT.md
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@ -49,7 +49,7 @@ runtime has only preformatted loc strings, no access to source text).
| 4 | `unknown function prinltn` / `unknown name n` | check.ml:6259, 2732 | `(prinltn "hi")` | B | C | D | B | No did-you-mean, although `near_miss` (check.ml:670) is written, tested and wired — to **types only**. Point it at `env.fns`, `env.globals` and the local scope. Cheapest structural win on the list. |
| 5 | `expected bool, found i32` | check.ml:1866 via `check_truthy` (3596) | `(let [x 1] (if x …))` | A | C | D | A | Caret is exactly right (the `check_truthy` loc work paid off). But the message never states Flan's truthiness rule — bool or dyn, nothing else — and never names the fix (`(not= x 0)`). Special-case the condition position. |
| 6 | `binding 5 has no value — let takes name/value pairs` | parse.ml:670 | `(let [x i32 5] …)` | C | D | D | B | A type annotation in `let` is the single most natural thing for someone arriving from a typed language, and `let` has none. The message reads as if the user miscounted. Detect "middle form names a type" and say so: "`let` bindings take no type annotation — write `[x 5]`". |
| 7 | `get takes 2 arguments, given 1` against the **user's own** `(defn get [p P] …)` | check.ml:5296 (builtin dispatch) + 6233 | `(defn get [p P] i32 …)` + `(get p)` | D | D | D | B | A user defn whose name collides with a builtin is silently shadowed, and then the arity refusal is measured against the *builtin*, pointing at the user's call. Either refuse the shadowing definition at its `dloc` with a note, or report the arity against the definition the user can see. |
| 7 | `get takes 2 arguments, given 1` against the **user's own** `(defn get [p P] …)` | check.ml:5296 (builtin dispatch) + 6233 | `(defn get [p P] i32 …)` + `(get p)` | D | D | D | B | A user defn whose name collides with a builtin is silently shadowed, and then the arity refusal is measured against the *builtin*, pointing at the user's call. Either refuse the shadowing definition at its `dloc` with a note, or report the arity against the definition the user can see. **Settled 2026-09-20, neither way: the author chose "allow shadowing but warn" — the defn wins at every call site in its own file and the compiler warns once at the definition. See FIX.org, "Shadowing a builtin".** |
| 8 | `unhandled Boom` | flan_rt.c:646 | `(defstruct Boom [why i32])` + `(error (Boom {.why 7}))`, `flan run` | D | C | D | B | Three words. No location (not even the `error` site, which the emitter knows), no field values, no list of the handlers that were in scope. The condition system is a headline feature and this is its failure mode. |
| 9 | `the collection nosuch: is a directory named nosuch somewhere above /…/. , and there is none` | load.ml:120 | `(import zz "nosuch:thing")` | B | C | C | D | Reads as an assertion immediately contradicted. Also emits a bare `/.` on the path. Rewrite as a plain statement of the search ("no directory named `nosuch` between here and the root") and list what collections *were* found. |
| 10 | `and`'s last operand gets the previous operand's caret | parse.ml `shortcircuit`, via check.ml:3632 | `(println (and true true (vec-new i32)))` | D | B | C | A | Already diagnosed in FIX.org:1036 with three rejected fixes; the accepted one — `check_if` preferring the arm that is not a compiler temp when choosing which to blame — is a check.ml change nobody owned. This pass owns check.ml. |

155
lib/check.ml
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@ -4932,35 +4932,18 @@ and call_value ctx ~want loc (callee : Tast.expr) args =
fail loc "this is a %s and not a function, so it cannot be called"
(Types.to_string other)
(* A builtin's arity, and the one thing the caret cannot show: whether the
count being measured against is the builtin's or a defn of the same name.
A defn does not shadow a builtin — the dispatch above reaches every builtin
arm before it ever looks in [fns] — so a user function called [get] is
silently unreachable, and the refusal that followed measured the call
against the builtin while pointing at a call the reader had written for
their own. Said outright, with the definition alongside. *)
and arity ctx loc name n args =
if List.length args <> n then begin
let notes =
if Hashtbl.mem ctx.env.fns name then
match Hashtbl.find_opt ctx.env.fn_locs name with
| Some at ->
[ Loc.note at
(name ^ " is also defined here, and this call is not reaching \
it — rename it to call it") ]
| None -> []
else []
in
let shadowed = notes <> [] in
if shadowed then
Loc.failk "check/builtin-arity" loc ~notes
"%s takes %d argument%s, given %d — this is the builtin %s, which a \
defn of the same name does not replace"
name n (if n = 1 then "" else "s") (List.length args) name
else
fail loc "%s takes %d argument%s, given %d" name n
(if n = 1 then "" else "s") (List.length args)
end
(* A builtin's arity. The count is the builtin's and can only be the
builtin's: a defn of the same name written in the program now takes the
call over before any builtin arm is reached ([shadows_builtin] at the top
of [named_call]), so a call measured here is a call to the builtin and
there is no second signature for the reader to have meant. The note that
used to say otherwise — "this is the builtin get, which a defn of the same
name does not replace" — described a resolution order this compiler no
longer has. *)
and arity _ctx loc name n args =
if List.length args <> n then
fail loc "%s takes %d argument%s, given %d" name n
(if n = 1 then "" else "s") (List.length args)
(* The operators that fold: [+ - * /], [min]/[max] and the three bitwise
combining operators all take two operands or more, and mean the same thing
@ -5350,6 +5333,19 @@ and vec_at ctx loc (target : Tast.expr) (idx : Ast.expr list) =
and named_call ctx ~want loc name args =
let prim p ty args = expect ctx loc ~want (mk loc ty (Tast.Prim (p, args))) in
match name with
(* The user's own definition, first — before every builtin arm below.
Clojure's rule: a [(defn get ...)] takes the name over, and a call
written in the program that defines it reaches that definition rather
than the builtin it is named after. The defn site is warned about once
(see [shadowed_builtins]); the call sites say nothing, because at a call
site there is nothing surprising left — the name means what the file
says it means.
What this arm does NOT do is let one file's definition reach into
another's: [shadows_builtin] answers false for a call in the prelude and
for a call in imported package code, which is the same visibility rule a
defn has everywhere else. *)
| _ when shadows_builtin ctx loc name -> ordinary_call ctx ~want loc name args
(* ── arithmetic and comparison ─────────────────────────────────── *)
| "+" | "-" | "*" | "/" ->
let p = match name with
@ -7163,13 +7159,22 @@ and named_call ctx ~want loc name args =
| _ -> prim (Tast.Cast target) target [ a ])
(* ── ordinary calls ────────────────────────────────────────────── *)
| _ -> ordinary_call ctx ~want loc name args
(* Everything that is not a builtin arm: a local of function type, a generic
signature, the function table, and the refusals for a name that is none of
them. Reached two ways — by falling past every arm above, and by the
shadowing guard at the very top of [named_call], which sends a call whose
name the program has defined straight here. One function so that both
routes resolve a name by exactly the same rules. *)
and ordinary_call ctx ~want loc name args =
match () with
(* A local or a parameter holding a function value, called by the name it is
bound to — which is what the body of [map] looks like. It is checked
before the global function table and after every builtin: a binding
shadows a defn of the same name (one namespace, ordinary lexical
scoping), and nothing shadows [+]. A local of any *other* type falls
through to the table, so a program that shadows a function name with an
i32 and then calls the function still means the function. *)
before the global function table: a binding shadows a defn of the same
name (one namespace, ordinary lexical scoping). A local of any *other*
type falls through to the table, so a program that shadows a function
name with an i32 and then calls the function still means the function. *)
| _ when (match lookup ctx name with
| Some b -> (match b.bty with Types.Fn _ -> true | _ -> false)
| None -> false) ->
@ -7251,6 +7256,43 @@ and named_call ctx ~want loc name args =
name name
else Loc.failk "check/unknown-function" loc "unknown function %s" name
(* Does the program's own definition of this name take this call over?
Three questions, and the order is the order that asks the fewest of them.
Is the name a builtin's at all. This is asked first and not second: it is
false for every call to an ordinary function, which is most calls in most
programs, and it is the question that stops the other two from running.
Asking it also keeps the arms that are not calls — an enum cast, a cast to
a type variable, a machine-type cast — exactly where they were, since a
name that reaches one of those is not a builtin's either.
Is it defined — by the function table, by a generic signature, or by a
local of function type. Two hash lookups and, only if both miss, the walk
down the scope, which is a list.
And is the definition visible here. Shadowing follows a defn's visibility
like anything else: the prelude is the language's own source and means the
builtin wherever it writes one, and an imported package's names are
qualified ([rl/get]) so a call written [get] inside one is the builtin
too — recognised by the owner's name, which the import qualified along
with everything else. Neither is shadowed by a definition in the file
being compiled, which is the point: a package that defines [get] does not
change what [get] means to its importer, and an importer that defines one
does not change what it means inside the package. *)
and shadows_builtin ctx loc name =
let defined () =
Hashtbl.mem ctx.env.fns name
|| Hashtbl.mem ctx.env.gsigs name
|| (match lookup ctx name with
| Some b -> (match b.bty with Types.Fn _ -> true | _ -> false)
| None -> false)
in
let visible () =
not (String.equal loc.Loc.file Prelude.file)
&& not (String.contains ctx.owner '/')
in
List.mem name !builtin_names && defined () && visible ()
(* ── A call to a generic function ───────────────────────────────────────
The whole of instantiation, and it is at the call site because the call
site is the only place the concrete types exist. Odin does the same thing
@ -7809,6 +7851,38 @@ let builtins : (string * string * string) list =
checked before this module is loaded. *)
let () = builtin_names := List.map (fun (n, _, _) -> n) builtins
(* ── The one thing shadowing owes the reader ────────────────────────────
A defn named after a builtin is legal and it wins ([shadows_builtin]), and
that is a large thing to have happened in silence: every [(get m k)] in
the file now means something the reader has to go and look at. So it is
said once, where the decision was made, and never again at the call sites
— a footgun notice, not a lint.
It is a warning and it says so in the one way that matters: nothing raises
and the exit status does not move. Unlike [memory_sites] it is behind no
flag, because there is nothing to tune — a program either renamed a
builtin or it did not, and the line is one line and rare.
The prelude is skipped: its defns are the language's own and a collision
there is a compiler bug rather than news for whoever is compiling. So are
qualified names, for the reason [shadows_builtin]'s [visible] gives —
[rl/get] is not [get] and shadows nothing. *)
let shadowed_builtins (decls : Ast.decl list) : Loc.diag list =
List.filter_map
(fun (d : Ast.decl) ->
match d.Ast.d with
| Ast.Defn fn
when List.mem fn.Ast.name !builtin_names
&& not (String.contains fn.Ast.name '/')
&& not (String.equal fn.Ast.nloc.Loc.file Prelude.file) ->
Some
(Loc.diag ~kind:"check/shadows-builtin" fn.Ast.nloc
(Printf.sprintf
"%s shadows the builtin %s — every call in this program now \
reaches your definition" fn.Ast.name fn.Ast.name))
| _ -> None)
decls
(* ── Declarations: pass 1, collect ─────────────────────────────────── *)
(* Constant folding, only over integers and only for defconst — enough for an
@ -9414,6 +9488,19 @@ let build_program ~keep_going (decls : Ast.decl list) : Tast.program * env =
be written anywhere in it, which is also what makes a reload rebuild
every dispatch from the session's declarations — see lib/classes.ml. *)
let decls = Classes.expand decls in
(* And with the declaration list in its final shape — the classes expanded,
the shims flattened, the imports already qualified by [Load] — the one
warning this compiler prints unasked. Here rather than in [bin/main.ml]
beside [print_memory_warnings] because every route into the compiler
passes through this function: build, check, run, and the dev daemon's
reload, which is where a defn is most likely to be written. Printed in
the shape [Loc] gives an error, so a checker in an editor parses it the
same way. *)
List.iter
(fun (d : Loc.diag) ->
prerr_endline
(Loc.entry ~mark:'~' ~label:"warning: " d.Loc.dloc d.Loc.dmsg))
(shadowed_builtins decls);
(* Pass one, and it stops at the first thing it refuses. That is not
laziness: every name, type and signature in the file comes from here, so a
declaration this pass could not make sense of leaves a hole that pass two

16
test/dune
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@ -56,6 +56,10 @@
(glob_files programs/pkgs/mac/*)
(glob_files programs/pkgs/macring/*)
(glob_files programs/pkgs/macspin/*)
; The package whose body calls the builtin get while the program importing
; it defines a get of its own — shadow-builtin.flan, which is the pin that
; a shadow stops at the file that declared it.
(glob_files programs/pkgs/shadowed/*)
; The synthetic C header the importer's table reads. Committed rather than
; reached for on the machine: the raylib case needs raylib installed, at the
; right version, with a variable set, so it skips everywhere and covers
@ -215,7 +219,9 @@
; And the macro-declaring packages, for the same reason.
(glob_files programs/pkgs/mac/*)
(glob_files programs/pkgs/macring/*)
(glob_files programs/pkgs/macspin/*))
(glob_files programs/pkgs/macspin/*)
; And the package shadow-builtin.flan imports.
(glob_files programs/pkgs/shadowed/*))
(action (run ./test_valgrind.exe)))
; The corpus a fourth time, through the hand-written x86-64 backend, compared
@ -272,7 +278,9 @@
(glob_files programs/pkgs/tree/*)
(glob_files programs/pkgs/mac/*)
(glob_files programs/pkgs/macring/*)
(glob_files programs/pkgs/macspin/*))
(glob_files programs/pkgs/macspin/*)
; And the package shadow-builtin.flan imports.
(glob_files programs/pkgs/shadowed/*))
(action
(setenv SURVEY_STRICT 1
(setenv SURVEY_QUIET 1
@ -435,7 +443,9 @@
(glob_files programs/pkgs/tree/*)
(glob_files programs/pkgs/mac/*)
(glob_files programs/pkgs/macring/*)
(glob_files programs/pkgs/macspin/*))
(glob_files programs/pkgs/macspin/*)
; And the package shadow-builtin.flan imports.
(glob_files programs/pkgs/shadowed/*))
(action
(setenv SURVEY_STRICT 1
(setenv SURVEY_QUIET 1

10
test/programs/pkgs/shadowed/shadowed.flan Normal file
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@ -0,0 +1,10 @@
;;;; A package that calls the builtin get, imported by a program that defines
;;;; a get of its own.
;;;;
;;;; The importer's defn takes the name over in the importer's own file and
;;;; nowhere else: this file's names were qualified at the import (this
;;;; function is shadowed/field to everything downstream), so the get written
;;;; here is the builtin's, was compiled as the builtin's, and answers what a
;;;; dyn map holds under a keyword.
(defn field [m] dyn (get m :b))

24
test/programs/shadow-builtin.flan Normal file
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@ -0,0 +1,24 @@
;;;; A defn named after a builtin, and what the name means afterwards.
;;;;
;;;; "Allow shadowing but warn": this file's (defn get ...) is legal, it wins
;;;; at every call site in this file, and the compiler says so once at the
;;;; definition — the warning is on stderr and the exit status does not move.
;;;;
;;;; Two calls, and between them the whole rule:
;;;;
;;;; - (get p) is one argument, which the builtin get does not take. It
;;;; compiles, and it prints the field, because the name resolves to the
;;;; definition below and the builtin is not consulted about its arity.
;;;; - (shadowed/field m) reaches into the imported package, whose body calls
;;;; the builtin get on a dyn map. The shadow does not follow it there: a
;;;; package's own calls mean what they meant when the package was written.
(import shadowed "pkgs/shadowed")
(defstruct P [x i32])
(defn get [p P] i32 (.x p))
(defn main [] ()
(println (get (P {.x 7})))
(println (shadowed/field {:a 1 :b 4})))

14
test/test_acceptance.ml
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@ -2475,6 +2475,20 @@ let () =
shape/Box and not area/shape/Box. *)
outputs "a diamond, with a type crossing it" "programs/pkg-diamond.flan"
"3\n6\n20\n";
(* A defn named after a builtin, and the boundary the shadow stops at.
The numbers are the whole claim and neither of them could be printed
by the other reading: 7 is the program's own one-argument (get p),
which the builtin get has no arity for at all, and 4 is the builtin
get called inside the imported package on a dyn map — the same name,
in one program, meaning two things because the package's names were
qualified at the import.
The warning the definition earns is on stderr and is pinned in
test_flan.ml, where the line and column can be asked about directly.
What is asserted here is that it changes nothing else: the program
runs and its status is zero. *)
outputs "a defn shadows a builtin, and the package it imports does not"
"programs/shadow-builtin.flan" "7\n4\n";
(* A data type crossing the same boundary, which was a refusal by name
until vendor/edn needed one. The rename has two halves and the second
is the one that is easy to do by accident only: the type's name is a

68
test/test_flan.ml
View File

@ -4311,25 +4311,38 @@ let () =
"(defn f [] i32 (let [x 1] (.r x)))"
~needle:"i32 is not a struct, so it has no fields";
(* A defn whose name is a builtin's is silently unreachable — the dispatch
reaches every builtin arm before it looks in the function table — and the
arity refusal was measured against the builtin while pointing at a call
the reader had written for their own. *)
(match diag_of "(defstruct P [x i32])\n(defn get [p P] i32 (.x p))\n (defn f [] i32 (let [p (P {.x 1})] (get p)))" with
| Some d ->
check "a shadowed builtin's arity has a kind"
(d.Loc.kind = "check/builtin-arity");
check "and says whose count it is"
(contains d.Loc.dmsg
"this is the builtin get, which a defn of the same name does not \
replace");
(match d.Loc.notes with
| [ n ] ->
check "and notes the definition that is not being reached"
(n.Loc.nloc.Loc.line = 2
&& contains n.Loc.nmsg "this call is not reaching it")
| _ -> check "a shadowed builtin has one note" false)
| None -> check "a shadowed builtin's call is refused" false);
(* "Allow shadowing but warn": a defn whose name is a builtin's is legal,
it wins at the call sites of the file that wrote it, and the compiler
says so once at the definition.
This used to be the other way round — the dispatch reached every builtin
arm before it looked in the function table, so the defn was silently
unreachable and the arity refusal carried a note saying so. That note
described a resolution order this compiler no longer has, and the source
below, which used to be refused, is the one that proves it: (get p) is
one argument, and the builtin get takes two. *)
let shadow_src =
"(defstruct P [x i32])\n(defn get [p P] i32 (.x p))\n\
(defn f [] i32 (let [p (P {.x 1})] (get p)))"
in
(match Check.shadowed_builtins (program shadow_src) with
| [ d ] ->
check "a defn named after a builtin is warned about, at the definition"
(d.Loc.kind = "check/shadows-builtin"
&& d.Loc.dloc.Loc.line = 2 && d.Loc.dloc.Loc.col = 7);
check "and the warning says what the name now means"
(d.Loc.dmsg
= "get shadows the builtin get — every call in this program now \
reaches your definition");
check "and it carries no notes, being one sentence about one decision"
(d.Loc.notes = [])
| _ -> check "a shadowing defn is warned about exactly once" false);
check "and the call reaches the defn, at the defn's arity"
(match checked shadow_src with
| _ -> true
| exception Loc.Error _ -> false);
check "a program that shadows nothing is warned at not at all"
(Check.shadowed_builtins (program "(defn f [] i32 1)") = []);
(* and's last operand is the then arm and the sentinel carrying the previous
operand's location is the else arm, so with no expectation in hand the
@ -4559,10 +4572,17 @@ let () =
There is no way to reflect over an OCaml match, so this reads the source
instead. The two regions are [named_call]'s arms and [var]'s, each from
its own [and] down to the first catch-all at the same indentation, and
the names are the string literals in the arm heads. It is a regex over
one file and costs nothing, which is why it is in the default run rather
than behind an alias. *)
its own [and] down to the catch-all at the same indentation, and the
names are the string literals in the arm heads. It is a regex over one
file and costs nothing, which is why it is in the default run rather
than behind an alias.
The catch-all is [ | _ ->] and not [ | _], because a guarded arm is
not one: [named_call] opens with [| _ when shadows_builtin ...], which
is a name the program defined taking its own call over, and stopping
there would read the region as empty and report every builtin as
undescribed. Guarded arms in between are skipped by the same rule that
skips a comment — they carry no string literal in the head. *)
let arm_names () =
let src =
In_channel.with_open_bin "../lib/check.ml" In_channel.input_all
@ -4591,7 +4611,7 @@ let () =
let rec take = function
| [] -> []
| l :: rest ->
if starts_with " | _" l then []
if starts_with " | _ ->" l then []
else if starts_with " | \"" l then quoted l @ take rest
else take rest
in