[PATCH 1/2] Add conversions to and from struct timespec to module interface.

[Philipp Stephani]

Time values are a fundamental data type, and such conversions are hard
to implement within modules because of the various forms of time
values in Emacs Lisp.  Adding dedicated conversion functions can
significantly simplify module code dealing with times.

This approach uses nanosecond precision.  While Emacs in theory has
support for higher-precision time values, in practice most languages
and standards, such as POSIX, C, Java, and Go, have settled on
nanosecond-precision integers to represent time.

* src/emacs-module.h.in: Add header for struct timespec.

* src/module-env-27.h: Add module functions for time conversion.

* src/emacs-module.c (module_extract_time, module_make_time): New
functions.
(initialize_environment): Use them.

* test/data/emacs-module/mod-test.c (Fmod_test_add_nanosecond): New
test function.
(emacs_module_init): Define it.

* test/src/emacs-module-tests.el (mod-test-add-nanosecond/valid)
(mod-test-add-nanosecond/nil, mod-test-add-nanosecond/invalid): New
unit tests.

* doc/lispref/internals.texi (Module Values): Document time
conversion functions.
---
 doc/lispref/internals.texi        | 22 ++++++++++++++++++++++
 etc/NEWS                          |  3 +++
 src/emacs-module.c                | 17 +++++++++++++++++
 src/emacs-module.h.in             |  1 +
 src/module-env-27.h               |  6 ++++++
 test/data/emacs-module/mod-test.c | 13 +++++++++++++
 test/src/emacs-module-tests.el    | 28 ++++++++++++++++++++++++++++
 7 files changed, 90 insertions(+)

diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index 25892d4b57..fb838113bc 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -1387,6 +1387,15 @@ Module Values
 @var{arg}, as a C @code{double} value.
 @end deftypefn
 
address@hidden Function struct timespec extract_time (emacs_env address@hidden, 
emacs_value @var{time})
+This function, which is available since Emacs 27, interprets
address@hidden as an Emacs time value and returns the corresponding
address@hidden timespec}.  @xref{Time of Day}.  This function signals an
+error if @var{time} is out of range for @code{struct timespec}.  If
address@hidden has higher precision than nanoseconds, then this function
+truncates it to nanosecond precision.
address@hidden deftypefn
+
 @deftypefn Function bool copy_string_contents (emacs_env address@hidden, 
emacs_value @var{arg}, char address@hidden, ptrdiff_t address@hidden)
 This function stores the UTF-8 encoded text of a Lisp string specified
 by @var{arg} in the array of @code{char} pointed by @var{buf}, which
@@ -1452,6 +1461,19 @@ Module Values
 corresponding Emacs floating-point value.
 @end deftypefn
 
address@hidden Function emacs_value make_time (emacs_env address@hidden, struct 
timespec @var{time})
+This function, which is available since Emacs 27, takes a @code{struct
+timespec} argument @var{time} and returns the corresponding Emacs
+timestamp.  @xref{Time of Day} for the possible return value formats.
+It is not specified in which timestamp format the time is returned,
+but it is always a valid Emacs timestamp.  The return value is exactly
+the same timestamp as @var{time}: all input values are representable,
+and there is never a loss of precision.  @code{time.tv_sec} and
address@hidden can be arbitrary values.  In particular, there's
+no requirement that @var{time} be normalized.  This means that
address@hidden doesn't have to be in the range [0, 999999999].
address@hidden deftypefn
+
 @deftypefn Function emacs_value make_string (emacs_env address@hidden, const 
char address@hidden, ptrdiff_t @var{strlen})
 This function creates an Emacs string from C text string pointed by
 @var{str} whose length in bytes, not including the terminating null
diff --git a/etc/NEWS b/etc/NEWS
index b13ab47768..2534262b62 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1910,6 +1910,9 @@ returns a regexp that never matches anything, which is an 
identity for
 this operation.  Previously, the empty string was returned in this
 case.
 
+** New module environment functions 'make_time' and 'extract_time' to
+convert between timespec structures and Emacs time values.
+
 
 * Changes in Emacs 27.1 on Non-Free Operating Systems
 
diff --git a/src/emacs-module.c b/src/emacs-module.c
index d7704efcf6..b798789351 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -74,6 +74,7 @@ To add a new module function, proceed as follows:
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
 
 #include "lisp.h"
 #include "dynlib.h"
@@ -734,6 +735,20 @@ module_process_input (emacs_env *env)
   return emacs_process_input_continue;
 }
 
+static struct timespec
+module_extract_time (emacs_env *env, emacs_value value)
+{
+  MODULE_FUNCTION_BEGIN ((struct timespec) {0});
+  return lisp_time_argument (value_to_lisp (value));
+}
+
+static emacs_value
+module_make_time (emacs_env *env, struct timespec time)
+{
+  MODULE_FUNCTION_BEGIN (NULL);
+  return lisp_to_value (env, make_lisp_time (time));
+}
+
 
 /* Subroutines.  */
 
@@ -1137,6 +1152,8 @@ initialize_environment (emacs_env *env, struct 
emacs_env_private *priv)
   env->vec_size = module_vec_size;
   env->should_quit = module_should_quit;
   env->process_input = module_process_input;
+  env->extract_time = module_extract_time;
+  env->make_time = module_make_time;
   Vmodule_environments = Fcons (make_mint_ptr (env), Vmodule_environments);
   return env;
 }
diff --git a/src/emacs-module.h.in b/src/emacs-module.h.in
index 009d1583fe..bfbe226dd9 100644
--- a/src/emacs-module.h.in
+++ b/src/emacs-module.h.in
@@ -22,6 +22,7 @@ along with GNU Emacs.  If not, see 
<https://www.gnu.org/licenses/>.  */
 
 #include <stdint.h>
 #include <stddef.h>
+#include <time.h>
 
 #ifndef __cplusplus
 #include <stdbool.h>
diff --git a/src/module-env-27.h b/src/module-env-27.h
index b491b60fbb..e63843f8d6 100644
--- a/src/module-env-27.h
+++ b/src/module-env-27.h
@@ -2,3 +2,9 @@
      function should quit.  */
   enum emacs_process_input_result (*process_input) (emacs_env *env)
     EMACS_ATTRIBUTE_NONNULL (1);
+
+  struct timespec (*extract_time) (emacs_env *env, emacs_value value)
+    EMACS_ATTRIBUTE_NONNULL (1);
+
+  emacs_value (*make_time) (emacs_env *env, struct timespec time)
+    EMACS_ATTRIBUTE_NONNULL (1);
diff --git a/test/data/emacs-module/mod-test.c 
b/test/data/emacs-module/mod-test.c
index a39e41afee..dbdbfecfe6 100644
--- a/test/data/emacs-module/mod-test.c
+++ b/test/data/emacs-module/mod-test.c
@@ -366,6 +366,18 @@ Fmod_test_sleep_until (emacs_env *env, ptrdiff_t nargs, 
emacs_value *args,
   return env->intern (env, "finished");
 }
 
+static emacs_value
+Fmod_test_add_nanosecond (emacs_env *env, ptrdiff_t nargs, emacs_value *args,
+                          void *data)
+{
+  assert (nargs == 1);
+  struct timespec time = env->extract_time (env, args[0]);
+  assert (time.tv_nsec >= 0);
+  assert (time.tv_nsec < 2000000000);  /* possible leap second */
+  time.tv_nsec++;
+  return env->make_time (env, time);
+}
+
 /* Lisp utilities for easier readability (simple wrappers).  */
 
 /* Provide FEATURE to Emacs.  */
@@ -434,6 +446,7 @@ emacs_module_init (struct emacs_runtime *ert)
   DEFUN ("mod-test-invalid-finalizer", Fmod_test_invalid_finalizer, 0, 0,
          NULL, NULL);
   DEFUN ("mod-test-sleep-until", Fmod_test_sleep_until, 2, 2, NULL, NULL);
+  DEFUN ("mod-test-add-nanosecond", Fmod_test_add_nanosecond, 1, 1, NULL, 
NULL);
 
 #undef DEFUN
 
diff --git a/test/src/emacs-module-tests.el b/test/src/emacs-module-tests.el
index 35aaaa64b6..eea4c61165 100644
--- a/test/src/emacs-module-tests.el
+++ b/test/src/emacs-module-tests.el
@@ -310,4 +310,32 @@ module--test-assertion
                       'finished))
         (quit)))))
 
+(ert-deftest mod-test-add-nanosecond/valid ()
+  (dolist (input (list
+                  ;; Some realistic examples.
+                  (current-time) (time-to-seconds)
+                  (encode-time 12 34 5 6 7 2019 t)
+                  ;; Various legacy timestamp forms.
+                  '(123 456) '(123 456 789) '(123 456 789 6000)
+                  ;; Corner case: this will result in a nanosecond
+                  ;; value of 1000000000 after addition.  The module
+                  ;; code should handle this correctly.
+                  '(123 65535 999999 999000)
+                  ;; Seconds since the epoch.
+                  123 123.45
+                  ;; New (TICKS . HZ) format.
+                  '(123456789 . 1000000000)))
+    (ert-info ((format "input: %s" input))
+      (should (time-equal-p (mod-test-add-nanosecond input)
+                            (time-add input '(0 0 0 1000)))))))
+
+(ert-deftest mod-test-add-nanosecond/nil ()
+  (should (<= (float-time (mod-test-add-nanosecond nil))
+              (+ (float-time) 1e-9))))
+
+(ert-deftest mod-test-add-nanosecond/invalid ()
+  (dolist (input '(1.0e+INF 1.0e-INF 0.0e+NaN (123) (123.45 6 7) "foo" [1 2]))
+    (ert-info ((format "input: %s" input))
+      (should-error (mod-test-add-nanosecond input)))))
+
 ;;; emacs-module-tests.el ends here
-- 
2.20.1 (Apple Git-117)