nix: repair flake for Nix 2.35 / macOS 26, modernize toolchain#1079
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The flake had rotted against current toolchains: - `nixpkgs` declared both a URL and a `follows`; Nix >= 2.25 rejects the ambiguity (the `follows` was what the lock resolved all along). - The opam `conf-git` check had no git in its build environment; give it one via the overlay, like the existing `conf-pkg-config` fix. - opam-nix (2025-01) referenced `darwin.apple_sdk`, removed from nixpkgs, and its pinned nixpkgs shipped binaries that macOS 26's dyld rejects (duplicate LC_RPATH). Update opam-nix to 2026-06. - The pinned provers (z3 4.12.6, cvc4 1.8, cvc5 1.0.9) no longer compile with the clang 19 that comes with the newer nixpkgs. Take z3 (4.15.1) and cvc5 (1.3.0) directly from nixpkgs and drop cvc4 (archived upstream), removing the source pins and the mkProverPackage machinery. While at it, modernize the toolchain: OCaml 4.14.2 -> 5.4.1 and Alt-Ergo 2.4.3 -> 2.6.3, with opam-repository advanced to 2026-07-14 (this also moves why3 to 1.8.2). Alt-Ergo 2.6.3's dune build invokes codesign on macOS, so the overlay's darwin.sigtool fix is extended to it. ci: bump install-nix-action to v31 so CI exercises a current Nix (v26's would not have caught the input conflict), cachix-action to v17.
bgregoir
approved these changes
Jul 15, 2026
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The flake had rotted against current toolchains:
nixpkgsdeclared both a URL and afollows; Nix >= 2.25 rejectsthe ambiguity (the
followswas what the lock resolved all along).conf-gitcheck had no git in its build environment; giveit one via the overlay, like the existing
conf-pkg-configfix.darwin.apple_sdk, removed fromnixpkgs, and its pinned nixpkgs shipped binaries that macOS 26's
dyld rejects (duplicate LC_RPATH). Update opam-nix to 2026-06.
compile with the clang 19 that comes with the newer nixpkgs. Take
z3 (4.15.1) and cvc5 (1.3.0) directly from nixpkgs and drop cvc4
(archived upstream), removing the source pins and the
mkProverPackage machinery.
While at it, modernize the toolchain: OCaml 4.14.2 -> 5.4.1 and
Alt-Ergo 2.4.3 -> 2.6.3, with opam-repository advanced to 2026-07-14
(this also moves why3 to 1.8.2). Alt-Ergo 2.6.3's dune build invokes
codesign on macOS, so the overlay's darwin.sigtool fix is extended
to it.
ci: bump install-nix-action to v31 so CI exercises a current Nix
(v26's would not have caught the input conflict), cachix-action
to v17.