Trade: implement Importer interfaces for the new MeshData.

Deprecating of the old ones comes later.

doc/changelog.dox

@@ -162,7 +162,8 @@ See also:
 
 -   A new, redesigned @ref Trade::MeshData class that allows much more flexible
     access to vertex/index data without unnecessary allocations and data
-    conversions or copies
+    conversions or copies. Importers expose it through the new
+    @ref Trade::AbstractImporter::mesh() family of APIs.
 -   Ability to import image mip levels via an additional parameter in
     @ref Trade::AbstractImporter::image2D(),
     @ref Trade::AbstractImporter::image2DLevelCount() and similar APIs for 1D

src/Magnum/Trade/AbstractImporter.cpp

@@ -38,6 +38,7 @@
 #include "Magnum/Trade/CameraData.h"
 #include "Magnum/Trade/ImageData.h"
 #include "Magnum/Trade/LightData.h"
+#include "Magnum/Trade/MeshData.h"
 #include "Magnum/Trade/MeshData2D.h"
 #include "Magnum/Trade/MeshData3D.h"
 #include "Magnum/Trade/ObjectData2D.h"
@@ -403,6 +404,59 @@ Containers::Pointer<ObjectData3D> AbstractImporter::doObject3D(UnsignedInt) {
     CORRADE_ASSERT(false, "Trade::AbstractImporter::object3D(): not implemented", {});
 }
 
+UnsignedInt AbstractImporter::meshCount() const {
+    CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::meshCount(): no file opened", {});
+    return doMeshCount();
+}
+
+UnsignedInt AbstractImporter::doMeshCount() const { return 0; }
+
+Int AbstractImporter::meshForName(const std::string& name) {
+    CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::meshForName(): no file opened", {});
+    return doMeshForName(name);
+}
+
+Int AbstractImporter::doMeshForName(const std::string&) { return -1; }
+
+std::string AbstractImporter::meshName(const UnsignedInt id) {
+    CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::meshName(): no file opened", {});
+    CORRADE_ASSERT(id < doMeshCount(), "Trade::AbstractImporter::meshName(): index" << id << "out of range for" << doMeshCount() << "entries", {});
+    return doMeshName(id);
+}
+
+std::string AbstractImporter::doMeshName(UnsignedInt) { return {}; }
+
+Containers::Optional<MeshData> AbstractImporter::mesh(const UnsignedInt id) {
+    CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::mesh(): no file opened", {});
+    CORRADE_ASSERT(id < doMeshCount(), "Trade::AbstractImporter::mesh(): index" << id << "out of range for" << doMeshCount() << "entries", {});
+    Containers::Optional<MeshData> mesh = doMesh(id);
+    CORRADE_ASSERT(!mesh || (!mesh->_indexData.deleter() && !mesh->_vertexData.deleter() && !mesh->_attributes.deleter()), "Trade::AbstractImporter::mesh(): implementation is not allowed to use a custom Array deleter", {});
+    return mesh;
+}
+
+Containers::Optional<MeshData> AbstractImporter::doMesh(UnsignedInt) {
+    CORRADE_ASSERT(false, "Trade::AbstractImporter::mesh(): not implemented", {});
+}
+
+MeshAttribute AbstractImporter::meshAttributeForName(const std::string& name) {
+    const MeshAttribute out = doMeshAttributeForName(name);
+    CORRADE_ASSERT(out == MeshAttribute{} || isMeshAttributeCustom(out),
+        "Trade::AbstractImporter::meshAttributeForName(): implementation-returned" << out << "is neither custom nor invalid", {});
+    return out;
+}
+
+MeshAttribute AbstractImporter::doMeshAttributeForName(const std::string&) {
+    return {};
+}
+
+std::string AbstractImporter::meshAttributeName(MeshAttribute name) {
+    CORRADE_ASSERT(isMeshAttributeCustom(name),
+        "Trade::AbstractImporter::meshAttributeName():" << name << "is not custom", {});
+    return doMeshAttributeName(meshAttributeCustom(name));
+}
+
+std::string AbstractImporter::doMeshAttributeName(UnsignedShort) { return {}; }
+
 UnsignedInt AbstractImporter::mesh2DCount() const {
     CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::mesh2DCount(): no file opened", {});
     return doMesh2DCount();

src/Magnum/Trade/AbstractImporter.h

@@ -159,8 +159,8 @@ expose internal state through various accessors:
     imported by @ref image1D(), @ref image2D() or @ref image3D()
 -   @ref LightData::importerState() can expose importer state for a light
     imported by @ref light()
--   @ref MeshData3D::importerState() can expose importer state for a mesh
-    imported by @ref mesh2D() or @ref mesh3D()
+-   @ref MeshData::importerState() can expose importer state for a mesh
+    imported by @ref mesh()
 -   @ref ObjectData3D::importerState() can expose importer state for an object
     imported by @ref object2D() or @ref object3D()
 -   @ref SceneData::importerState() can expose importer state for a scene
@@ -680,6 +680,72 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
          */
         Containers::Pointer<ObjectData3D> object3D(UnsignedInt id);
 
+        /**
+         * @brief Mesh count
+         * @m_since_latest
+         *
+         * Expects that a file is opened.
+         */
+        UnsignedInt meshCount() const;
+
+        /**
+         * @brief Mesh ID for given name
+         * @m_since_latest
+         *
+         * If no mesh for given name exists, returns @cpp -1 @ce. Expects that
+         * a file is opened.
+         * @see @ref meshName()
+         */
+        Int meshForName(const std::string& name);
+
+        /**
+         * @brief Mesh name
+         * @param id        Mesh ID, from range [0, @ref meshCount()).
+         * @m_since_latest
+         *
+         * Expects that a file is opened.
+         * @see @ref meshForName()
+         */
+        std::string meshName(UnsignedInt id);
+
+        /**
+         * @brief Mesh
+         * @param id        Mesh ID, from range [0, @ref meshCount()).
+         * @m_since_latest
+         *
+         * Returns given mesh or @ref Containers::NullOpt if importing failed.
+         * Expects that a file is opened.
+         */
+        Containers::Optional<MeshData> mesh(UnsignedInt id);
+
+        /**
+         * @brief Mesh attribute for given name
+         * @m_since_latest
+         *
+         * If the name is not recognized, returns a zero (invalid)
+         * @ref MeshAttribute, otherwise returns a custom mesh attribute. Note
+         * that the value returned by this function may depend on whether a
+         * file is opened or not and also be different for different files ---
+         * see documentation of a particular importer for more information.
+         * @see @ref isMeshAttributeCustom()
+         */
+        MeshAttribute meshAttributeForName(const std::string& name);
+
+        /**
+         * @brief String name for given custom mesh attribute
+         * @m_since_latest
+         *
+         * Given a custom @p name returned by @ref mesh() in a @ref MeshData,
+         * returns a string identifier. If a string representation is not
+         * available or @p name is not recognized, returns an empty string.
+         * Expects that @p name is custom. Note that the value returned by
+         * this function may depend on whether a file is opened or not and also
+         * be different for different files --- see documentation of a
+         * particular importer for more information.
+         * @see @ref isMeshAttributeCustom()
+         */
+        std::string meshAttributeName(MeshAttribute name);
+
         /**
          * @brief Two-dimensional mesh count
          *
@@ -1164,6 +1230,53 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
         /** @brief Implementation for @ref object3D() */
         virtual Containers::Pointer<ObjectData3D> doObject3D(UnsignedInt id);
 
+        /**
+         * @brief Implementation for @ref meshCount()
+         * @m_since_latest
+         *
+         * Default implementation returns @cpp 0 @ce.
+         */
+        virtual UnsignedInt doMeshCount() const;
+
+        /**
+         * @brief Implementation for @ref meshForName()
+         * @m_since_latest
+         *
+         * Default implementation returns @cpp -1 @ce.
+         */
+        virtual Int doMeshForName(const std::string& name);
+
+        /**
+         * @brief Implementation for @ref meshName()
+         * @m_since_latest
+         *
+         * Default implementation returns an empty string.
+         */
+        virtual std::string doMeshName(UnsignedInt id);
+
+        /**
+         * @brief Implementation for @ref mesh()
+         * @m_since_latest
+         */
+        virtual Containers::Optional<MeshData> doMesh(UnsignedInt id);
+
+        /**
+         * @brief Implementation for @ref meshAttributeForName()
+         * @m_since_latest
+         *
+         * Default implementation returns an invalid (zero) value.
+         */
+        virtual MeshAttribute doMeshAttributeForName(const std::string& name);
+
+        /**
+         * @brief Implementation for @ref meshAttributeName()
+         * @m_since_latest
+         *
+         * Receives the custom ID extracted via @ref meshAttributeCustom(MeshAttribute).
+         * Default implementation returns an empty string.
+         */
+        virtual std::string doMeshAttributeName(UnsignedShort name);
+
         /**
          * @brief Implementation for @ref mesh2DCount()
          *

src/Magnum/Trade/MeshData.h

@@ -44,11 +44,16 @@ namespace Magnum { namespace Trade {
 @brief Mesh attribute name
 @m_since_latest
 
-@see @ref MeshData, @ref MeshAttributeData, @ref VertexFormat
+@see @ref MeshData, @ref MeshAttributeData, @ref VertexFormat,
+    @ref AbstractImporter::meshAttributeForName(),
+    @ref AbstractImporter::meshAttributeName()
 */
 /* 16 bits because 8 bits is not enough to cover all potential per-edge,
    per-face, per-instance and per-meshlet attributes */
 enum class MeshAttribute: UnsignedShort {
+    /* 0 reserved for an invalid value (returned from
+       AbstractImporter::meshAttributeForName()) */
+
     /**
      * Position. Type is usually @ref Magnum::Vector2 "Vector2" for 2D and
      * @ref Magnum::Vector3 "Vector3" for 3D. Corresponds to
@@ -57,7 +62,7 @@ enum class MeshAttribute: UnsignedShort {
      *      @ref MeshData::positions2DAsArray(),
      *      @ref MeshData::positions3DAsArray()
      */
-    Position,
+    Position = 1,
 
     /**
      * Normal. Type is usually @ref Magnum::Vector3 "Vector3". Corresponds to
@@ -243,7 +248,8 @@ class MAGNUM_TRADE_EXPORT MeshAttributeData {
 @m_since_latest
 
 Provides access to mesh vertex and index data, together with additional
-information such as primitive type.
+information such as primitive type. Populated instances of this class are
+returned from @ref AbstractImporter::mesh().
 
 @section Trade-MeshData-usage Basic usage
 
@@ -268,6 +274,8 @@ of data, which you can directly upload, and then use provided metadata to let
 the GPU know of the format and layout:
 
 @snippet MagnumTrade.cpp MeshData-usage-advanced
+
+@see @ref AbstractImporter::mesh()
 */
 class MAGNUM_TRADE_EXPORT MeshData {
     public:
@@ -441,7 +449,9 @@ class MAGNUM_TRADE_EXPORT MeshData {
          * @brief Attribute name
          *
          * The @p id is expected to be smaller than @ref attributeCount() const.
-         * @see @ref attributeFormat(), @ref isMeshAttributeCustom()
+         * @see @ref attributeFormat(), @ref isMeshAttributeCustom(),
+         *      @ref AbstractImporter::meshAttributeForName(),
+         *      @ref AbstractImporter::meshAttributeName()
          */
         MeshAttribute attributeName(UnsignedInt id) const;
 
@@ -714,6 +724,11 @@ class MAGNUM_TRADE_EXPORT MeshData {
         const void* importerState() const { return _importerState; }
 
     private:
+        /* For custom deleter checks. Not done in the constructors here because
+           the restriction is pointless when used outside of plugin
+           implementations. */
+        friend AbstractImporter;
+
         UnsignedInt attributeFor(MeshAttribute name, UnsignedInt id) const;
 
         UnsignedInt _vertexCount;

src/Magnum/Trade/Test/AbstractImporterTest.cpp

@@ -37,6 +37,7 @@
 #include "Magnum/Trade/CameraData.h"
 #include "Magnum/Trade/ImageData.h"
 #include "Magnum/Trade/LightData.h"
+#include "Magnum/Trade/MeshData.h"
 #include "Magnum/Trade/MeshData2D.h"
 #include "Magnum/Trade/MeshData3D.h"
 #include "Magnum/Trade/MeshObjectData2D.h"
@@ -156,6 +157,25 @@ struct AbstractImporterTest: TestSuite::Tester {
     void object3DNoFile();
     void object3DOutOfRange();
 
+    void mesh();
+    void meshCountNotImplemented();
+    void meshCountNoFile();
+    void meshForNameNotImplemented();
+    void meshForNameNoFile();
+    void meshNameNotImplemented();
+    void meshNameNoFile();
+    void meshNameOutOfRange();
+    void meshNotImplemented();
+    void meshNoFile();
+    void meshOutOfRange();
+    void meshCustomIndexDataDeleter();
+    void meshCustomVertexDataDeleter();
+    void meshCustomAttributesDeleter();
+
+    void meshAttributeName();
+    void meshAttributeNameNotImplemented();
+    void meshAttributeNameNotCustom();
+
     void mesh2D();
     void mesh2DCountNotImplemented();
     void mesh2DCountNoFile();
@@ -371,6 +391,25 @@ AbstractImporterTest::AbstractImporterTest() {
               &AbstractImporterTest::object3DNoFile,
               &AbstractImporterTest::object3DOutOfRange,
 
+              &AbstractImporterTest::mesh,
+              &AbstractImporterTest::meshCountNotImplemented,
+              &AbstractImporterTest::meshCountNoFile,
+              &AbstractImporterTest::meshForNameNotImplemented,
+              &AbstractImporterTest::meshForNameNoFile,
+              &AbstractImporterTest::meshNameNotImplemented,
+              &AbstractImporterTest::meshNameNoFile,
+              &AbstractImporterTest::meshNameOutOfRange,
+              &AbstractImporterTest::meshNotImplemented,
+              &AbstractImporterTest::meshNoFile,
+              &AbstractImporterTest::meshOutOfRange,
+              &AbstractImporterTest::meshCustomIndexDataDeleter,
+              &AbstractImporterTest::meshCustomVertexDataDeleter,
+              &AbstractImporterTest::meshCustomAttributesDeleter,
+
+              &AbstractImporterTest::meshAttributeName,
+              &AbstractImporterTest::meshAttributeNameNotImplemented,
+              &AbstractImporterTest::meshAttributeNameNotCustom,
+
               &AbstractImporterTest::mesh2D,
               &AbstractImporterTest::mesh2DCountNotImplemented,
               &AbstractImporterTest::mesh2DCountNoFile,
@@ -2031,6 +2070,287 @@ void AbstractImporterTest::object3DOutOfRange() {
     CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::object3D(): index 8 out of range for 8 entries\n");
 }
 
+void AbstractImporterTest::mesh() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+        Int doMeshForName(const std::string& name) override {
+            if(name == "eighth") return 7;
+            else return -1;
+        }
+        std::string doMeshName(UnsignedInt id) override {
+            if(id == 7) return "eighth";
+            else return {};
+        }
+        Containers::Optional<MeshData> doMesh(UnsignedInt id) override {
+            /* Verify that initializer list is converted to an array with
+               the default deleter and not something disallowed */
+            if(id == 7) return MeshData{MeshPrimitive::Points, nullptr, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}, &state};
+            else return {};
+        }
+    } importer;
+
+    CORRADE_COMPARE(importer.meshCount(), 8);
+    CORRADE_COMPARE(importer.meshForName("eighth"), 7);
+    CORRADE_COMPARE(importer.meshName(7), "eighth");
+
+    auto data = importer.mesh(7);
+    CORRADE_VERIFY(data);
+    CORRADE_COMPARE(data->importerState(), &state);
+}
+
+void AbstractImporterTest::meshCountNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+    } importer;
+
+    CORRADE_COMPARE(importer.meshCount(), 0);
+}
+
+void AbstractImporterTest::meshCountNoFile() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.meshCount();
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshCount(): no file opened\n");
+}
+
+void AbstractImporterTest::meshForNameNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+    } importer;
+
+    CORRADE_COMPARE(importer.meshForName(""), -1);
+}
+
+void AbstractImporterTest::meshForNameNoFile() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.meshForName("");
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshForName(): no file opened\n");
+}
+
+void AbstractImporterTest::meshNameNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    CORRADE_COMPARE(importer.meshName(7), "");
+}
+
+void AbstractImporterTest::meshNameNoFile() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.meshName(42);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshName(): no file opened\n");
+}
+
+void AbstractImporterTest::meshNameOutOfRange() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.meshName(8);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshName(): index 8 out of range for 8 entries\n");
+}
+
+void AbstractImporterTest::meshNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(7);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): not implemented\n");
+}
+
+void AbstractImporterTest::meshNoFile() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(42);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): no file opened\n");
+}
+
+void AbstractImporterTest::meshOutOfRange() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(8);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): index 8 out of range for 8 entries\n");
+}
+
+void AbstractImporterTest::meshCustomIndexDataDeleter() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 1; }
+        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+            return MeshData{MeshPrimitive::Triangles, Containers::Array<char>{data, 1, [](char*, std::size_t) {}}, MeshIndexData{MeshIndexType::UnsignedByte, data}};
+        }
+
+        char data[1];
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(0);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): implementation is not allowed to use a custom Array deleter\n");
+}
+
+void AbstractImporterTest::meshCustomVertexDataDeleter() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 1; }
+        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+            return MeshData{MeshPrimitive::Triangles, Containers::Array<char>{nullptr, 0, [](char*, std::size_t) {}}, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}};
+        }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(0);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): implementation is not allowed to use a custom Array deleter\n");
+}
+
+void AbstractImporterTest::meshCustomAttributesDeleter() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 1; }
+        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+            return MeshData{MeshPrimitive::Triangles, nullptr, Containers::Array<MeshAttributeData>{&positions, 1, [](MeshAttributeData*, std::size_t) {}}};
+        }
+
+        MeshAttributeData positions{MeshAttribute::Position, VertexFormat::Vector3, nullptr};
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+
+    importer.mesh(0);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): implementation is not allowed to use a custom Array deleter\n");
+}
+
+void AbstractImporterTest::meshAttributeName() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+
+        MeshAttribute doMeshAttributeForName(const std::string& name) override {
+            if(name == "SMOOTH_GROUP_ID") return meshAttributeCustom(37);
+            return MeshAttribute{};
+        }
+
+        std::string doMeshAttributeName(UnsignedShort id) override {
+            if(id == 37) return "SMOOTH_GROUP_ID";
+            return "";
+        }
+    } importer;
+
+    CORRADE_COMPARE(importer.meshAttributeForName("SMOOTH_GROUP_ID"), meshAttributeCustom(37));
+    CORRADE_COMPARE(importer.meshAttributeName(meshAttributeCustom(37)), "SMOOTH_GROUP_ID");
+}
+
+void AbstractImporterTest::meshAttributeNameNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    CORRADE_COMPARE(importer.meshAttributeForName(""), MeshAttribute{});
+    CORRADE_COMPARE(importer.meshAttributeName(meshAttributeCustom(37)), "");
+}
+
+void AbstractImporterTest::meshAttributeNameNotCustom() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+
+        MeshAttribute doMeshAttributeForName(const std::string&) override {
+            return MeshAttribute::Position;
+        }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    importer.meshAttributeForName("SMOOTH_GROUP_ID");
+    importer.meshAttributeName(MeshAttribute::Position);
+    CORRADE_COMPARE(out.str(),
+        "Trade::AbstractImporter::meshAttributeForName(): implementation-returned Trade::MeshAttribute::Position is neither custom nor invalid\n"
+        "Trade::AbstractImporter::meshAttributeName(): Trade::MeshAttribute::Position is not custom\n");
+}
+
 void AbstractImporterTest::mesh2D() {
     struct: AbstractImporter {
         ImporterFeatures doFeatures() const override { return {}; }