deps: document which ICU version we work with

[srl295]

in nodejs/Intl#35 I wrote:

I think node will work with a pretty wide range of ICUs at this point. It might be worth actually testing this, and making sure configure complains if the ICU is too old.

Probably ICU4C 58.2 is the minimum for master ( ad72142 ish ) at this point. It would be 57 if #19656 were solved.

Note that the backlevel ICU versions are relevant to packagers trying to use the pre-installed ICU from the system or other packaging. For example, Ubuntu stretch (at least on raspbian) has ICU 57.1 installed.

must be 99 ways to overengineer this

• Just document the ICU version
  • in configure with the relevant options?
  • in tools/icu/README.md (doesn't seem helpful)
  • in doc/api/intl.md (best option?)
  • in the wiki?
• warn in configure if the version is too old
• error in configure if the version is too old
  • … with an option to override?

[ryzokuken]

@nodejs/documentation this has been open for quite a while. PTAL.

[ryzokuken]

/cc @vsemozhetbyt

[vsemozhetbyt]

Sorry, I do not have the required knowledge to handle this(

[ryzokuken]

@vsemozhetbyt that's okay, I just wanted to ask if you think we should mention the version in the docs. I could help you with the actual change? Or I could make it myself, but would need the docs teams' help in order to keep it updated.

[vsemozhetbyt]

I have no opinion on this.
Let's also cc @nodejs/intl

[ryzokuken]

I'd rather cc @nodejs/i18n. intl has been archived in favor of i18n.

[ryzokuken]

That said, they must've pinged intl because docs didn't exist, but this looks like 100% a docs thingie.

[srl295]

• doc/api/intl.md should say 'ICU 57.1 is the current minimum version'
• configure should probably warn (not fail) if the minimum seems to be too old.

actually even better would be that configure --help prints out the minimum recommended version ( as part of the intl options help text) and doc/api/intl.md tells you to look there.

[srl295]

How does this look?

$ ./configure --help
…
    --with-icu-source=WITH_ICU_SOURCE
                        Intl mode: optional local path to icu/ dir, or
                        path/URL of the icu4c source archive. v57.x or later
                        recommended.

$ ./configure --with-icu-source=https://ssl.icu-project.org/files/icu4c/49.1.1/icu4c-49_1_1-src.tgz
creating icu_config.gypi
Deleting old ICU source: deps/icu
 <https://ssl.icu-project.org/files/icu4c/49.1.1/icu4c-49_1_1-src.tgz>
 Fetch: . 18.6MB total, 18.6MB downloaded
 Extracting tarfile: deps/icu-tmp/icu4c-49_1_1-src.tgz
* Using ICU in deps/icu
WARNING: icu4c v49.x may be too old, v57.x or later is recommended.
creating icu_config.gypi
{ 'target_defaults': { 'cflags': [],
                       'default_configuration': 'Release',
                       'defines': [],
                       'include_dirs': [],
                       'libraries': []},
  'variables': { 'asan': 0,
                 'build_v8_with_gn': 'false',
                 'coverage': 'false',
…
…
creating config.gypi
creating config.mk
WARNING: warnings were emitted in the configure phase