WKT2_2018: always export ID in base crs node, even if there is one on upper node

This is a particular logic allowed by paragraph 7.3.3 Identifier
of OGC 18-010r6

6 files changed, 81 insertions, 3 deletions

diff --git a/include/proj/io.hpp b/include/proj/io.hpp
index 90163001..ace8ad9d 100644
--- a/include/proj/io.hpp
+++ b/include/proj/io.hpp
@@ -302,6 +302,8 @@ class PROJ_GCC_DLL WKTFormatter {
     PROJ_INTERNAL bool primeMeridianOrParameterUnitOmittedIfSameAsAxis() const;
     PROJ_INTERNAL bool primeMeridianInDegree() const;
     PROJ_INTERNAL bool outputCSUnitOnlyOnceIfSame() const;
+    PROJ_INTERNAL bool idOnTopLevelOnly() const;
+    PROJ_INTERNAL bool topLevelHasId() const;
 
     /** WKT version. */
     enum class Version {
diff --git a/src/iso19111/crs.cpp b/src/iso19111/crs.cpp
index 9779d817..2dc6b3bf 100644
--- a/src/iso19111/crs.cpp
+++ b/src/iso19111/crs.cpp
@@ -2432,7 +2432,8 @@ void DerivedCRS::baseExportToWKT(io::WKTFormatter *formatter,
                                           !l_baseCRS->identifiers().empty());
     formatter->addQuotedString(l_baseCRS->nameStr());
     l_baseCRS->exportDatumOrDatumEnsembleToWkt(formatter);
-    if (formatter->use2018Keywords() && formatter->outputId()) {
+    if (formatter->use2018Keywords() &&
+        !(formatter->idOnTopLevelOnly() && formatter->topLevelHasId())) {
         l_baseCRS->formatID(formatter);
     }
     formatter->endNode();
@@ -2673,7 +2674,8 @@ void ProjectedCRS::_exportToWKT(io::WKTFormatter *formatter) const {
             geodeticCRSAxisList[0]->unit()._exportToWKT(formatter);
         }
         l_baseCRS->primeMeridian()->_exportToWKT(formatter);
-        if (formatter->use2018Keywords() && formatter->outputId()) {
+        if (formatter->use2018Keywords() &&
+            !(formatter->idOnTopLevelOnly() && formatter->topLevelHasId())) {
             l_baseCRS->formatID(formatter);
         }
         formatter->endNode();
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index 220ee967..78b18719 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -634,6 +634,18 @@ bool WKTFormatter::primeMeridianInDegree() const {
 
 // ---------------------------------------------------------------------------
 
+bool WKTFormatter::idOnTopLevelOnly() const {
+    return d->params_.idOnTopLevelOnly_;
+}
+
+// ---------------------------------------------------------------------------
+
+bool WKTFormatter::topLevelHasId() const {
+    return d->stackHasId_.size() >= 2 && d->stackHasId_[1];
+}
+
+// ---------------------------------------------------------------------------
+
 WKTFormatter::Version WKTFormatter::version() const {
     return d->params_.version_;
 }
diff --git a/test/cli/testprojinfo_out.dist b/test/cli/testprojinfo_out.dist
index a2e2cab9..ee9aeca7 100644
--- a/test/cli/testprojinfo_out.dist
+++ b/test/cli/testprojinfo_out.dist
@@ -633,7 +633,8 @@ PROJCRS["Monte Mario (Rome) / Italy zone 1",
             ELLIPSOID["International 1924",6378388,297,
                 LENGTHUNIT["metre",1]]],
         PRIMEM["Rome",12.4523333333333,
-            ANGLEUNIT["degree",0.0174532925199433]]],
+            ANGLEUNIT["degree",0.0174532925199433]],
+        ID["EPSG",4806]],
     CONVERSION["Italy zone 1",
         METHOD["Transverse Mercator",
             ID["EPSG",9807]],
diff --git a/test/unit/test_crs.cpp b/test/unit/test_crs.cpp
index bfd6ee66..d7303df9 100644
--- a/test/unit/test_crs.cpp
+++ b/test/unit/test_crs.cpp
@@ -1601,6 +1601,52 @@ TEST(crs, projectedCRS_as_WKT2) {
 
 // ---------------------------------------------------------------------------
 
+TEST(crs, projectedCRS_as_WKT2_2018) {
+    auto crs = createProjected();
+
+    auto expected =
+        "PROJCRS[\"WGS 84 / UTM zone 31N\",\n"
+        "    BASEGEOGCRS[\"WGS 84\",\n"
+        "        DATUM[\"World Geodetic System 1984\",\n"
+        "            ELLIPSOID[\"WGS 84\",6378137,298.257223563,\n"
+        "                LENGTHUNIT[\"metre\",1]]],\n"
+        "        PRIMEM[\"Greenwich\",0,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433]],\n"
+        "        ID[\"EPSG\",4326]],\n"
+        "    CONVERSION[\"UTM zone 31N\",\n"
+        "        METHOD[\"Transverse Mercator\",\n"
+        "            ID[\"EPSG\",9807]],\n"
+        "        PARAMETER[\"Latitude of natural origin\",0,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433],\n"
+        "            ID[\"EPSG\",8801]],\n"
+        "        PARAMETER[\"Longitude of natural origin\",3,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433],\n"
+        "            ID[\"EPSG\",8802]],\n"
+        "        PARAMETER[\"Scale factor at natural origin\",0.9996,\n"
+        "            SCALEUNIT[\"unity\",1],\n"
+        "            ID[\"EPSG\",8805]],\n"
+        "        PARAMETER[\"False easting\",500000,\n"
+        "            LENGTHUNIT[\"metre\",1],\n"
+        "            ID[\"EPSG\",8806]],\n"
+        "        PARAMETER[\"False northing\",0,\n"
+        "            LENGTHUNIT[\"metre\",1],\n"
+        "            ID[\"EPSG\",8807]]],\n"
+        "    CS[Cartesian,2],\n"
+        "        AXIS[\"(E)\",east,\n"
+        "            ORDER[1],\n"
+        "            LENGTHUNIT[\"metre\",1]],\n"
+        "        AXIS[\"(N)\",north,\n"
+        "            ORDER[2],\n"
+        "            LENGTHUNIT[\"metre\",1]],\n"
+        "    ID[\"EPSG\",32631]]";
+
+    EXPECT_EQ(
+        crs->exportToWKT(
+            WKTFormatter::create(WKTFormatter::Convention::WKT2_2018).get()),
+        expected);
+}
+// ---------------------------------------------------------------------------
+
 TEST(crs, projectedCRS_as_WKT2_simplified) {
     auto crs = createProjected();
 
diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index 2181b321..17b3c334 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -1663,6 +1663,21 @@ TEST(wkt_parse, wkt2_2018_projected_with_id_in_basegeodcrs) {
     ASSERT_TRUE(crs != nullptr);
     ASSERT_EQ(crs->baseCRS()->identifiers().size(), 1U);
     EXPECT_EQ(crs->baseCRS()->identifiers().front()->code(), "4326");
+
+    {
+        auto got_wkt = crs->exportToWKT(
+            WKTFormatter::create(WKTFormatter::Convention::WKT2_2018).get());
+        EXPECT_TRUE(got_wkt.find("ID[\"EPSG\",4326]]") != std::string::npos)
+            << got_wkt;
+    }
+
+    {
+        auto got_wkt = crs->exportToWKT(
+            WKTFormatter::create(WKTFormatter::Convention::WKT2_2018_SIMPLIFIED)
+                .get());
+        EXPECT_TRUE(got_wkt.find("ID[\"EPSG\",4326]]") == std::string::npos)
+            << got_wkt;
+    }
 }
 
 // ---------------------------------------------------------------------------