@cImport Fails with gmp_sprintf for mpfr_t Variadic Args

[fmozza]

Zig Version

0.14.0-dev.3222+8a3aebaee:

Steps to Reproduce and Observed Behavior

Description

In Zig 0.14.0, gmp_sprintf via @cImport fails to format mpfr_t arguments (from MPC) with %Rf, outputting the format string (%Rf, 3 chars) instead of the value. It works correctly with mpf_t (GMP) and %Ff.

Steps to Reproduce

1. Install Zig 0.14.0, libgmp-dev, libmpfr-dev, libmpc-dev on Ubuntu.
2. Use the attached demo.zig and build.zig.
3. Run zig build run --verbose.

Observed Behavior

mpf_t: 3.141589999999999882618340052431449294090270996093, wrote: 52 mpfr_t: %Rf, wrote: 3

• mpf_t works as expected.
• mpfr_t outputs %Rf instead of the value.

Environment

• Zig: 0.14.0
• OS: Ubuntu 24.04
• GMP: 6.3.0
• MPFR: 4.2.1
• MPC: 1.3.1

Expected Behavior

Expected Behavior

• mpf_t: Formats as 3.14159... (GMP float).
• mpfr_t: Formats as 2.718... (MPFR float from MPC).

bug_demo.zip