Honor SOURCE_DATE_EPOCH

Fixes #67

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [unreleased]
+### Added
+- Honor `SOURCE_DATE_EPOCH` in `BUILT_TIME_UTC`
+
 ## [0.7.3] - 2024-05-21
 ### Added
 - Search for lockfile in manifest's parent directory (crates in workspaces)

src/krono.rs

@@ -23,10 +23,32 @@ pub fn strptime(s: &str) -> chrono::DateTime<chrono::offset::Utc> {
         .with_timezone(&chrono::offset::Utc)
 }
 
+fn get_source_date_epoch_from_env() -> Option<chrono::DateTime<chrono::offset::Utc>> {
+    match std::env::var("SOURCE_DATE_EPOCH") {
+        Ok(val) => {
+            let ts = match val.parse::<i64>() {
+                Ok(ts) => ts,
+                Err(_) => {
+                    eprintln!("SOURCE_DATE_EPOCH defined, but not a i64");
+                    return None;
+                }
+            };
+            match chrono::DateTime::from_timestamp(ts, 0) {
+                Some(now) => Some(now),
+                None => {
+                    eprintln!("SOURCE_DATE_EPOCH can't be represented as a UTC-time");
+                    None
+                }
+            }
+        }
+        Err(_) => None,
+    }
+}
+
 pub fn write_time(mut w: &fs::File) -> io::Result<()> {
     use io::Write;
 
-    let now = chrono::offset::Utc::now();
+    let now = get_source_date_epoch_from_env().unwrap_or_else(chrono::offset::Utc::now);
     write_str_variable!(
         w,
         "BUILT_TIME_UTC",

src/lib.rs

@@ -286,6 +286,11 @@
 //! The build-time is recorded as `BUILT_TIME_UTC`. If `built` is included as a runtime-dependency,
 //! it can parse the string-representation into a `time:Tm` with the help of
 //! `built::util::strptime()`.
+//!
+//! `built` honors the environment variable `SOURCE_DATE_EPOCH`. If the variable is defined and
+//! parses to a valid UTC timestamp, that build-time is used instead of the current local time.
+//! The variable is silently ignored if defined but but does not parse to a valid UTC timestamp.
+//!
 //! ```
 //! /// The built-time in RFC2822, UTC
 //! pub const BUILT_TIME_UTC: &str = "Wed, 27 May 2020 18:12:39 +0000";

tests/testbox_tests.rs

@@ -468,6 +468,60 @@ fn main() {
     p.create_and_run(&[]);
 }
 
+#[test]
+fn source_date_epoch() {
+    let mut p = Project::new();
+    let built_root = get_built_root();
+
+    p.add_file(
+        "Cargo.toml",
+        format!(
+            r#"
+[package]
+name = "testbox"
+version = "1.2.3-rc1"
+authors = ["Joe", "Bob", "Harry:Potter"]
+build = "build.rs"
+description = "xobtset"
+
+[dependencies]
+built = {{ path = {:?}, features=["chrono"] }}
+
+[build-dependencies]
+built = {{ path = {:?}, features=["chrono"] }}"#,
+            &built_root, &built_root
+        ),
+    );
+
+    p.add_file(
+        "build.rs",
+        r#"
+use std::env;
+
+fn main() {
+    // Set timestamp
+    env::set_var("SOURCE_DATE_EPOCH", "1716639359");
+
+    built::write_built_file().unwrap();
+}"#,
+    );
+
+    p.add_file(
+        "src/main.rs",
+        r#"
+mod built_info {
+    include!(concat!(env!("OUT_DIR"), "/built.rs"));
+}
+
+fn main() {
+    assert_eq!(built::util::strptime(built_info::BUILT_TIME_UTC).to_rfc2822(),
+              "Sat, 25 May 2024 12:15:59 +0000");
+    println!("builttestsuccess");
+}"#,
+    );
+    p.create_and_run(&[]);
+}
+
 #[test]
 #[cfg(feature = "git2")]
 fn git_no_git() {