Set SOURCE_DATE_EPOCH

[harens]

Closes: https://trac.macports.org/ticket/59672

This PR allows base to define the SOURCE_DATE_EPOCH environment variable to assist with reproducible builds. The value can be manually set in a portfile via the source_date_epoch variable.

If the variable isn't assigned, its value is set to the greatest Unix timestamp of the files present in the source code (credit to Ryan for implementation details).

[harens]

Just to show how powerful SOURCE_DATE_EPOCH is, I've pushed a commit that standardises the file modification timestamps produced by MacPorts archives.

I tested this with a port I maintain, ioping. I ran sudo port -ds archive ioping twice, and then compared the archives using diffoscope.

Before this PR: File timestamps are different, so the archives are as well.

$ gsha256sum ioping-1.3_0.darwin_21.arm64\ 2.tbz2
6135d8dff9c87a3074fbf1dbaeea13db4ab0ef7774bcd5072e1c5196246d7396  ioping-1.3_0.darwin_21.arm64 2.tbz2
$ gsha256sum ioping-1.3_0.darwin_21.arm64.tbz2
6958d0826cc9c0d2775f3d9f9c20372f2c2fa5369caa44f80b7fbc4746504743  ioping-1.3_0.darwin_21.arm64.tbz2

Afterwards: The archives are completely identical.

$ gsha256sum ioping-1.3_0.darwin_21.arm64\ 2.tbz2
2406a76abc668c91ef9ec066ab9735dbee55ceba615ea6ec15aff6537d6d71ce  ioping-1.3_0.darwin_21.arm64 2.tbz2
$ gsha256sum ioping-1.3_0.darwin_21.arm64.tbz2
2406a76abc668c91ef9ec066ab9735dbee55ceba615ea6ec15aff6537d6d71ce  ioping-1.3_0.darwin_21.arm64.tbz2

Below is the diffoscope output showing how the timestamps in the original archives are different:

@@ -1,14 +1,14 @@
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./
--rw-r--r--   0 root         (0) wheel        (0)      287 2023-02-25 12:13:31.000000 ./+STATE
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./
+-rw-r--r--   0 root         (0) wheel        (0)      287 2023-02-25 12:13:03.000000 ./+STATE
 -rw-r--r--   0 root         (0) wheel        (0)     1039 2022-09-04 11:18:25.000000 ./+PORTFILE
--rw-r--r--   0 root         (0) wheel        (0)      405 2023-02-25 12:13:31.000000 ./+CONTENTS
--rw-r--r--   0 root         (0) wheel        (0)      152 2023-02-25 12:13:31.000000 ./+DESC
--rw-r--r--   0 root         (0) wheel        (0)       39 2023-02-25 12:13:31.000000 ./+COMMENT
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/local/
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/local/bin/
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/local/share/
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/local/share/man/
-drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:31.000000 ./opt/local/share/man/man1/
--r--r--r--   0 root         (0) wheel        (0)     3603 2023-02-25 12:13:31.000000 ./opt/local/share/man/man1/ioping.1.gz
--rwxr-xr-x   0 root         (0) wheel        (0)    73539 2023-02-25 12:13:31.000000 ./opt/local/bin/ioping
+-rw-r--r--   0 root         (0) wheel        (0)      405 2023-02-25 12:13:03.000000 ./+CONTENTS
+-rw-r--r--   0 root         (0) wheel        (0)      152 2023-02-25 12:13:03.000000 ./+DESC
+-rw-r--r--   0 root         (0) wheel        (0)       39 2023-02-25 12:13:03.000000 ./+COMMENT
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/local/
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/local/bin/
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/local/share/
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/local/share/man/
+drwxr-xr-x   0 root         (0) wheel        (0)        0 2023-02-25 12:13:03.000000 ./opt/local/share/man/man1/
+-r--r--r--   0 root         (0) wheel        (0)     3603 2023-02-25 12:13:03.000000 ./opt/local/share/man/man1/ioping.1.gz
+-rwxr-xr-x   0 root         (0) wheel        (0)    73539 2023-02-25 12:13:03.000000 ./opt/local/bin/ioping

[harens]

~~Seem to be a lot of "failed to extract" errors:~~

error: failed to extract dependencies-b: /private/tmp/macports-tests/opt/local/var/macports/build/_users_runner_work_macports-base_macports-base_tests_test_dependencies-b/dependencies-b/work/dependencies-b-1: no such file or directory
...
Error: Failed to extract envvariables: /private/tmp/macports-tests/opt/local/var/macports/build/_Users_runner_work_macports-base_macports-base_tests_test_envvariables/envvariables/work/envvariables-1: no such file or directory
...
etc.

~~Any help debugging appreciated.~~

EDIT: Fix incoming.

[ryandesign]

Took me a minute of reading the code, but I see now that you implemented:

1. setting SOURCE_DATE_EPOCH during all phases, and
2. changing the timestamp of all files in the archive to that value

In the ticket I was only proposing doing (1) and I don't know what the consequences are of doing (2).

[harens]

Took me a minute of reading the code, but I see now that you implemented:

1. setting `SOURCE_DATE_EPOCH` during all phases, and

2. changing the timestamp of all files in the archive to that value

In the ticket I was only proposing doing (1) and I don't know what the consequences are of doing (2).

Thank you for the review Ryan, you make a very valid point. I think the easiest thing for now is to simply add SOURCE_DATE_EPOCH to base as was discussed in the original ticket. Standardising the timestamps can be discussed at a later date.