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Twelve names sit on the wrong side of our unit boundary — the second sign of a class whose first sign is fixed

The class has two signs and they point opposite ways

Two seats hit it within an hour, from opposite directions, and neither instance names the other:

sign what the declaration does measured fix direction
shadow takes away a capability we already have frankD, f5ad23c32 — uses sysutils closed dynamic-array Delete/Insert for essentially every program in the tree remove the declaration (done, frankH, 475528dae)
only home is the sole place the capability exists frankS, today — DynArraySize at lib/rtl/sysutils.pas:733/:5695; tarray13 fails at line 23 with undefined variable (DynArraySize), and one uses sysutils line advances it to line 68 add the name to the implicit surface

Same root — the unit boundary is drawn in the wrong place — and the same tell, one uses line changing the answer. frankS's warning is why this row exists: "a fix that only handles the shadowing sign will read as complete." It nearly did: the shadow direction is now closed for sysutils with a control (frankH intersected the 15 SoftIntrinsicOpen names with sysutils' declarations — ['Delete', 'Insert'] at HEAD, [] after the commit, same script both trees, so a [] meaning "my regex broke" would have shown as [] on both), and nothing in that result mentions the other twelve.

The twelve

AllocMem   DynArraySize   Error       LowerCase
SetString  StrLen         StrPas      StringOfChar
SysBackTraceStr   UTF8Decode   UTF8Encode   sLineBreak

Reachable here after all, so NOT gaps: Concat, Copy, Pos, UpCase (parser intrinsics) and HexStr (ambient unit export). Copy, UpCase and Pos were independently measured clear by frankD while narrowing the shadow.

The predicate, published — both halves are required

tools/rtl_unit_boundary_census.py reproduces this. 167 routines in our sysutils interface → 17 fpc resolves ambiently → 5 of those are ambiently reachable here too → 12.

Half one, the fpc side. The oracle is fpc itself, not a grep of its sources. Compile a one-statement program with no uses clause and read one discriminator: whether fpc says Identifier not found. Any other outcome — wrong parameter count, a type error, success — means the name RESOLVED. Grepping systemh.inc answers what one header spells and misses everything reaching system through the include chain or through objpas. Note what this is complete about: it is "an fpc program does not need uses sysutils for this", which is the question we care about, and it is not literally "the name is in system" — objpas counts too.

Half two, the pxx side, and it is what takes 17 to 12. Of the fpc-ambient names, which can a pxx program use with no uses clause: a parser intrinsic (CaseEqual(name, 'X') across the four pasparser_*.inc) or a routine an ambient unit's interface exports (compiler/builtin/builtin.pas, builtinheap.pas).

Controls, all branched on — the census exits 3 rather than printing a result. The fpc-side controls are probed DIRECTLY rather than looked for in the output, which matters: the first version required Delete and Insert to appear among our declarations, and 475528dae removed both hours later, so it exited 3 on a tree where nothing was wrong. A control that encodes a defect stops being a control the moment the defect is fixed. Now: Delete/Insert/DynArraySize must resolve under fpc and Format/IntToStr/UpperCase/ChangeFileExt must not; a nonsense identifier must come back not-found on both sides, or every answer either side gives is "yes"; Copy/Pos/UpCase must come back reachable HERE; not every candidate may come back reachable; and DynArraySize must survive into the gap list.

Those pxx-side controls earned themselves, and the story is the reason they are there (frankH): two earlier probe shapes — if @Length = nil then ; and a bare Length; — each reported all 17 of 17 absent, because neither shape is how pxx resolves an intrinsic. "A census reporting ALL of its candidates is the tell", and without Copy/Pos/UpCase as must-find rows the list would have been seventeen names that were really "my probe cannot see intrinsics".

Two independent measurements, and they are genuinely two

frankH and this seat measured the fpc side with different probe shapes (if @X = nil then ; under -Mobjfpc -Sh, versus a bare X; statement under both {$mode fpc} and {$mode objfpc}) on different trees (before and after 475528dae), and got the same 17/5/12 split, name for name. Those two can fail differently — an address-of probe is defeated by anything whose address cannot be taken, a statement probe by anything that is not a statement — so the agreement is corroboration rather than one method run twice.

What is NOT established, and it is the larger half

Nobody has shown that any of the other eleven breaks a real program. Only DynArraySize has a vehicle (tarray13). The rest is the reachability question, which is exactly the half that got the ESP fork wrong this morning by never being asked. Two rows need a look before they are treated as RTL gaps at all:

The other ten look clean.

Where the other side is

There is no lib/rtl/system.pas in this tree. The implicit surface is compiler/builtin/builtin.pas + builtinheap.pas, which already exports at least one fpc-facing unprefixed name — GetFPCHeapStatus — so the precedent for putting a system name there exists rather than needing to be invented (frankS). EspBareBoot is the only profile that excludes the builtin unit (ParseUsesUnitAmbient('builtinheap') in pasparser_prog.inc), and on it uses sysutils does not compile at all, so the ESP trade-off the decide row carried was void in both ESP profiles (frankH).

Provenance, per item

The shadow sign, f5ad23c32, and the Copy/UpCase/Pos clearance are frankD's. DynArraySize's two sites, tarray13's line 23 → line 68, the two-signs reading and the GetFPCHeapStatus precedent are frankS's, measured on tarray13 today. The removal 475528dae, the shadow-direction completeness control, the pxx-side half of the predicate and its three must-find rows, and the sLineBreak/Error caveats are frankH's. The committed census, its fpc-side oracle and the independent confirmation of the 17/5/12 split are this seat's, run at HEAD on fpc 3.2.2. The classification of the twelve is nobody's yet.

Resolution, 2026-09-09 (frankS)

What was measured, and it is the half the ticket refused to skip

The census named a POPULATION. A per-name probe turned it into a defect list: one no-uses program per name, compiled against fpc 3.2.2 and against pxx, the discriminator being undefined variable on our side. Eleven of the twelve ran; all eleven were real.

name               fpc (no uses)   pxx, before      pxx, after
AllocMem           ok 0            undefined var    ok 0
DynArraySize       ok 5            undefined var    ok 5
SetString          ok abc          undefined var    ok abc
sLineBreak         ok 1            undefined var    ok 1
UTF8Decode         ok 3            undefined var    ok 3
UTF8Encode         ok abc          undefined var    ok abc
LowerCase          ok abc          undefined var    undefined var   (pin)
StrLen             ok 2            undefined var    undefined var   (pin)
StrPas             ok ab           undefined var    undefined var   (pin)
StringOfChar       ok xxxx         undefined var    undefined var   (pin)
SysBackTraceStr    ok 19           undefined var    undefined var   (pin)
Error              not probed      --               --              (deps)

Error is the twelfth and stays unprobed on purpose: it is a compiler-internal name here as well, and FPC's Error is tied into the runtime error path, so it needs sysutils' exception hierarchy before the question is even well posed.

There were TWO holes, not one, and the second is a different scan

The program-level pre-scan in pasparser_prog.inc reads the program's own tokens. Adding the six triggers there made a no-uses PROGRAM work and left a no-uses UNIT still failing, because the unit's tokens are never in that scan. pasparser_proc.inc needed its own unitNeedsBuiltinSys clause. That is the third instance of the same shape — the math/thread surface was the first, the Classes enumerators the second — so the class is about the SCAN being per-file, not about any of the three name sets.

The five that stayed, and why it is not a ranking

lib/rtl is built with the pinned compiler against a frozen copy of compiler/builtin/ — make lib-test prints exactly that on its second line, "isolates track A's compiler/builtin/ edits". So a name MOVED out of lib/rtl/sysutils.pas is gone from the only place that build can resolve it. With all eleven moved, make lib-test failed every unit with undefined variable (LowerCase), raised from inside sysutils.pas itself.

The consumer grep that produced the first four covered lib/ and examples/ and not the test/lib_ rows, which are lib-test rows built the same way — so StringOfChar cost a second identical failure at lib_strpchar.pas:49. The population for this question is everything the pinned build compiles, not everything under lib/.

Inert until pinned — say it here rather than wait for it

The six moved names work at HEAD and are invisible to anything building with $(PXX_STABLE) until the next pin carries them. Nothing in lib/** depends on that, because the moved six are exactly the ones nothing in that build calls — which is the same criterion, read the other way round.

Landed

Log

CORRECTION, 2026-09-09, hours after the resolution above (frankS)

The "two holes, two scans" half of this resolution was wrong and is retracted. The six names, the probe, the eleven-of-twelve classification and the pin-shaped split are unaffected.

I added a unit-level trigger (unitNeedsBuiltinSys, pasparser_proc.inc) believing a no-uses UNIT could not otherwise reach the moved names. It is dead code and has been removed.

The control I did not run, and what it says

Disable one pull, rebuild, run test_unit_ambient_system_surface:

pull disabled result
unit-level builtin compiles, every row prints — the clause could never fail
unit-level math refused at pi — that clause is load-bearing

Any uses clause pulls builtin (the tkUses arm, which my own comment in builtin.pas already said), and a unit is only ever compiled because a program uses it — pxx refuses a standalone unit outright. So builtin is in scope before any unit is parsed. math is different: nothing pulls it for you, which is why the earlier fix needed a unit-level clause and this one did not.

Confirmed independently with a name that has no trigger in either scan: VariantTagName, declared in builtin.pas, is refused from a no-uses PROGRAM and compiles fine from a no-uses UNIT.

Why I believed it — AND THIS TICKET'S TWO FINDINGS WERE ONE OBSERVATION

Read top to bottom this ticket looks like it found two independent things: a unit-level ambient hole and a frozen-builtin split. They are one observation, read twice. make lib-test failed every unit with undefined variable (LowerCase) while only the program-level trigger existed. That single failure is the entire evidence for both readings, and only the second one is true — the pinned build cannot see a name moved out of lib/rtl.

The error string is doing the work a discriminator should do. undefined variable (X) is what a missing ambient pull says and what a name missing from the frozen builtin says, so the message cannot separate them and I picked the hypothesis already in hand. The fixture I then wrote to prove the unit-level reading passes with or without the clause, so it could not separate them either — it certified the belief instead of testing it.

The discriminator, when it was finally run, is not a better error message but a differential build: disable one pull, rebuild, see which fixture moves.

What is left of the class claim

Two instances, not three: the math/thread surface and the Classes enumerators. The shape is still "an ambient unit that nothing pulls for you", and the six names never had it — builtin is pulled by every uses clause there is.

frank-coordinator's probe is what started this: it found UniqueString and RunError reaching a no-uses unit while sitting in the program scan only, and said plainly that it had NOT established they were the same mechanism. They were not, and the question it flagged is the one that turned out to matter.

2026-09-11 — the third round, and the thing all three have in common

Three times in this ticket the criterion was right and the population was wrong, each time widening by exactly one group nobody had thought of:

round missed group how it announced itself
1 lib/rtl calling its own declarations undefined variable (LowerCase), every unit
2 the test/lib_ rows undefined variable (StringOfChar) at lib_strpchar.pas:49
3 external/ undefined variable (SetString) in external/synapse/synautil.pas

The first two failed on the box that made the change, in the run written to clear it, which is why they cost minutes. The third did not, and cost two days, because external/ is absent on plexus and make lib-test skips what it cannot find. It is not silent about that — the last line of a green run says SKIPPED: synapse-ssl ... (green here does NOT cover them) — and the skip notice was read as bookkeeping rather than as the scope of the green.

A green that names its own skips is still a green about a smaller corpus, and the sentence that says so is the one nobody reads. The cheap fix is not a better grep: it is tools/install_externals.sh before the run, so there is nothing to skip and the local gate covers the population the claim is about.

Second thing worth keeping: the first positive control I wrote for this was invalid and passed. Reverting lib/rtl/sysutils.pas into a scratch directory and pointing -Fu at it did NOT reproduce the failure, because the pinned compiler resolves lib/rtl through an exe-dir-relative path of its own (stable_linux_amd64/default/../../lib/rtl) before it consults -Fu for a transitively used unit — so the control was measuring the live tree while appearing to measure the reverted one. A direct uses sysutils program DID fail against the same scratch copy, which is what made the shadow look like a real result. The control that works is to revert the file in place (patch out, measure, patch back). Another instrument correct about something else.