feat: add missing PhoneNumberToCarrierMapper feature that is available in java version

[wmundev]

Changes

• feat: add missing PhoneNumberToCarrierMapper feature that is available in java version

[Copilot]

Pull request overview

Adds a C# implementation of carrier-name lookup to bring the library closer to libphonenumber’s Java feature set, reusing the existing prefix-mapping/resource-loading model already used for offline geocoding.

Changes:

• Add PhoneNumberToCarrierMapper and shared PrefixFileReader support for carrier prefix data from embedded folders or zip resources.
• Expose PhoneNumberUtil.IsMobileNumberPortableRegion and add unit tests covering production, synthetic, and zipped carrier datasets.
• Wire carrier resources into project files, CI/build scripts, ignore rules, and README usage/testing documentation.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
csharp/PhoneNumbers/PrefixFileReader.cs	New shared loader for prefix-based mapping data used by carrier lookups.
csharp/PhoneNumbers/PhoneNumbers.csproj	Embeds carrier resources similarly to geocoding resources.
csharp/PhoneNumbers/PhoneNumberUtil.cs	Adds region-level mobile-number-portability lookup API.
csharp/PhoneNumbers/PhoneNumberToCarrierMapper.cs	Introduces the public carrier-mapper API and singleton access.
csharp/PhoneNumbers.Test/TestPhoneNumberToCarrierMapper.cs	Adds production/test/zipped-path coverage for carrier lookup behavior.
csharp/PhoneNumbers.Test/PhoneNumbers.Test.csproj	Embeds test carrier resources and zipped test archive.
appveyor.yml	Updates Windows CI packaging steps for carrier resources.
README.md	Documents carrier lookup usage and local test zip generation.
.gitignore	Ignores generated carrier zip artifacts.
.github/workflows/run_all_tests_and_upload_code_coverage.yml	Generates zipped test carrier data for Windows GitHub Actions.
.github/workflows/build_and_run_unit_tests_linux.yml	Generates zipped test carrier data for Linux GitHub Actions.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 12 changed files in this pull request and generated 2 comments.

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[codecov]

Codecov Report

❌ Patch coverage is 93.10345% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.85%. Comparing base (06ddfbe) to head (aec7dd5).

Files with missing lines	Patch %	Lines
csharp/PhoneNumbers/PrefixFileReader.cs	93.61%	2 Missing and 4 partials ⚠️
csharp/PhoneNumbers/PhoneNumberUtil.cs	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #317      +/-   ##
==========================================
+ Coverage   75.27%   75.85%   +0.58%     
==========================================
  Files          34       36       +2     
  Lines        4424     4540     +116     
  Branches     1001     1028      +27     
==========================================
+ Hits         3330     3444     +114     
+ Misses        885      883       -2     
- Partials      209      213       +4     

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[twcclegg]

C-1. NANPA carrier lookups always return empty in production

This ports Java's 4-digit NANPA split (1650, 1242, …), which is correct only when the data has been pre-split per area code into a binary blob — Java's
build pipeline does that, the C# port doesn't.

The shipped data at resources/carrier/en/1.txt is a single 728-line file with full prefix entries (1242357|BaTelCo, 1242462|BaTelCo, …). The only NANPA
key that ever lands in MappingFileProvider.countryCallingCodes is 1, so Array.BinarySearch(..., 1650) returns negative, GetFileName returns "", and
every +1 … carrier lookup against GetInstance() returns "".

The existing PhoneNumberOfflineGeocoder.cs:418-426 already saw this and commented out the same split, replacing it with var phonePrefix =
countryCallingCode; — relying on AreaCodeMap.Lookup(number) to do the longest-prefix match against the full national number. The geocoder consumes the
same single-file shape from resources/geocoding/en/1.txt.

The test suite hides this:

• TestGetNameForFixedOrMobileNumber (line 198-204) asserts "" for +1 6502530000 against GetInstance() — passes for the wrong reason.
• resources/test/carrier/en/1.txt was renamed to 1650.txt to satisfy the test lookup path.

Fix: drop the NANPA split (mirror geocoder line 426): var phonePrefix = countryCallingCode;. Then add a regression test that calls
GetInstance().GetNameForValidNumber for an actual NANPA prefix in the shipped en/1.txt (e.g. Bahamas +1 242 357 xxxx → "BaTelCo").

-Claude

[twcclegg]

Claude's recommended fix:

-            // prefix of 4 digits for NANPA instead, e.g. 1650.
-            var phonePrefix = countryCallingCode != 1
-                ? countryCallingCode
-                : (int)(1000 + number.NationalNumber / 10000000);
+            // Java pre-splits NANPA data into 4-digit-keyed blobs (e.g. 1650) at build time. The C#
+            // port ships the source .txt files unsplit, so a single en/1.txt holds every NANPA entry
+            // and AreaCodeMap's longest-prefix lookup matches against the full national number.
+            // Mirrors PhoneNumberOfflineGeocoder, which made the same trade-off.
+            var phonePrefix = countryCallingCode;```

[twcclegg]

It seems odd that this was renamed. Claude wants to rename it back.

[twcclegg]

Furthermore it'll get named by automatically when the next release overwrites the resources folder.

[wmundev]

thanks, no worries, i'll rename it back, i changed it originally because the NANPA test cases weren't covered