7f3bd69bd9
Any assignment / compound-assignment whose target chain is ROOTED at a
constant — a const-flagged global (array consts, #run consts) or a
module value const (struct consts incl.) — diagnoses 'cannot assign
through constant X' at compile time. A struct const's field write used
to compile and bus-error at runtime (issue 0116); scalars misfired
silently. A deref along the chain (p.*) breaks the root — pointer
writes stay the documented escape until the const-ness steps; a local
shadowing the const name stays writable.
Also: typed struct constants ('W : Color : Color.{...}') register —
the shape list skipped struct_literal, leaving the typed form
unresolved while the untyped one worked.
Examples: 1162 (all rejection shapes incl. the 0116 crash repro),
0178 (typed struct const reads + copy independence).
1.7 KiB
0116 — writes through module consts are not rejected (struct-const write bus-errors at runtime)
RESOLVED (2026-06-11, PLAN-CONST-AGG step 2). The assignment lowering rejects any target chain ROOTED at a constant — a const-flagged global (array consts, #run consts) or a module value const (struct consts incl.) — with
cannot assign through constant 'X'. A deref along the chain (p.*) breaks the root (pointer writes stay the documented escape until the const-ness steps); a local shadowing the const name stays writable. Regression test: examples/1162-diagnostics-const-write-rejected.sx (struct field — the crash repro, array element, compound, bare scalar).
Symptom. Assigning through a module-level constant compiles silently. For a struct-literal const the store lands in read-only memory and the program crashes at runtime.
- Observed: compiles;
Bus errorat runtime on the store. - Expected: compile-time diagnostic —
cannot assign through constant 'WHITE'.
Reproduction
#import "modules/std.sx";
Color :: struct { r, g, b: s64; }
WHITE :: Color.{ r = 255, g = 255, b = 255 };
main :: () {
WHITE.r = 0; // compiles; bus error at runtime
print("{}\n", WHITE.r);
}
(Copies are fine and stay fine: w := WHITE; w.r = 0; mutates the copy.)
Fix
Scheduled as step 2 of current/PLAN-CONST-AGG.md (aggregate consts):
one rejection rule for assignment/compound-assignment targets whose ROOT
identifier resolves to a module const (module_const_map author) or a
const-flagged global (the array consts that plan introduces). Diagnose at
the assignment site; pin the repro above as a diagnostics example.