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fn main() {
// docs.rs builds documentation in a network-blocked sandbox and may lack a
// matching FFmpeg dev environment, so the crate compiles its FFI call sites
// as stubs there (see the `#[cfg(docsrs)]` / `#[cfg(not(docsrs))]` gates
// throughout `src/`). docs.rs sets `DOCS_RS=1` in the build environment;
// mirror that into a `docsrs` cfg so those stubs are selected only on docs.rs.
//
// `docsrs` is deliberately NOT a Cargo feature. A Cargo feature is enabled by
// `--all-features`, which would compile the stubs into an ordinary build — and
// those stubs skip the real FFmpeg calls, leaving a binary that segfaults the
// moment it opens a file. Keying off `DOCS_RS` instead means a normal
// `cargo build`/`test`/`run` (with or without `--all-features`) always compiles
// the real FFmpeg path; only docs.rs ever sees the stubs. (The stubs guard
// rustdoc's type-check, not runtime — docs.rs never executes this code.)
println!("cargo:rerun-if-env-changed=DOCS_RS");
if std::env::var_os("DOCS_RS").is_some() {
println!("cargo:rustc-cfg=docsrs");
}
// `docsrs` is a well-known cfg name, but declare it explicitly so the
// `unexpected_cfgs` lint stays quiet across toolchains.
println!("cargo:rustc-check-cfg=cfg(docsrs)");
// ffmpeg-sys-next (`links = "ffmpeg"`) publishes one `cargo:KEY=VALUE`
// metadata entry per probed FFmpeg version / API macro, and Cargo hands
// those to direct dependents as `DEP_FFMPEG_*` environment variables.
// Re-emit the true ones as plain cfgs (`ffmpeg_8_0`, `ffmpeg_7_1`, ...)
// so sources can gate on the FFmpeg actually linked — the same mechanism
// ffmpeg-next's build.rs uses for its version features. Keys with an
// empty value mark versions/macros the linked FFmpeg does NOT have; they
// still get a check-cfg declaration so e.g. `#[cfg(ffmpeg_8_0)]` lints
// clean when building against FFmpeg 7.x.
// vars_os + explicit UTF-8 filtering: plain env::vars() would panic the
// whole build script on an unrelated non-UTF-8 environment variable.
for (name, value) in std::env::vars_os() {
let (Ok(name), Ok(value)) = (name.into_string(), value.into_string()) else {
continue;
};
if let Some(key) = name.strip_prefix("DEP_FFMPEG_") {
let key = key.to_lowercase();
// Metadata keys are snake_case idents today; skip anything that
// would not form a valid cfg name rather than break the build.
if key.is_empty()
|| key.starts_with(|c: char| c.is_ascii_digit())
|| !key.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')
{
continue;
}
println!("cargo:rustc-check-cfg=cfg({key})");
if value == "true" {
println!("cargo:rustc-cfg={key}");
}
}
}
// Belt and suspenders: ffmpeg-sys-next does emit this key even on
// docs.rs (it probes whatever FFmpeg the build image ships), but if some
// environment ever yields no DEP_FFMPEG_* metadata at all, the cfgs the
// sources reference must still be declared for unexpected_cfgs.
println!("cargo:rustc-check-cfg=cfg(ffmpeg_8_0)");
}