[ASDAlexander77]

Problem

testConstraint emitted "Type X does not satisfy the constraint Y." itself, before the caller could decide whether the failure was an error. Two cases were wrong:

• Type-predicate guards in the DefaultLib. __is<V extends T, T> and __is_any<V extends never> fail their constraint on purpose, and the call folds to false (MLIRGenGenerics.cpp). They still warned from inside lib.generics.ts, so every reduce whose accumulator type differs from the element type warned, and so did every Map with a non-string key (HashHelper.hashCode).
• The inference-only call in zipTypeParameterWithArgument. Its result is ignored and the constraint is checked again later, but it warned anyway. Because of that, a real violation warned twice: Type 1 ... and Type s32 ....

Fix

testConstraint takes a new bool reportFailure = true parameter:

• The final check in the instantiation passes !isTypePredicate.
• The inference call passes false.

Verification

• lines.reduce((m, line) => Math.max(m, w(line)), 0.0) and new Map<int, string>() with m.set/m.get compile under --emit=jit (without --nowarn) with no warnings, and still print 6 and a.
• function f<T extends string>(t: T) { return t; } print(f(1)); now gives a single warning, Type s32 does not satisfy the constraint string.
• New tests under test/tester/constraint-warning/:
  • test-compile-constraint-warning-type-predicate: self-contained isOf/isAny predicates, inferred and explicit. It fails on any warning.
  • test-compile-constraint-warning-violation: the single s32 warning must appear, and Type 1 ... must not.
  • Both fail against the previous compiler.
• ctest -C Release -j 8 --timeout 300: 4126/4126 passed.

Follow-up (not in this PR)

native_ts_graphics can turn two text-width loops into reduce calls that no longer warn. This was tried and reverted on 2026-10-17 because of this warning.

• examples/mouse_cursor.ts (centered): lines.reduce((w, line) => Math.max(w, Donut_ImGuiCalcTextWidth(line)), 0.0)
• examples/raytracing_ao.ts (menu box): this.menuLines.reduce((w, menuLine) => Math.max(w, Donut_ImGuiCalcTextWidth(menuLine)), 0.0)

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