Add Preview support (#19)

src/main/kotlin/androidx/compose/material/icons/generator/IconWriter.kt

@@ -32,6 +32,7 @@ class IconWriter(
     private val icons: Collection<Icon>,
     private val groupClass: ClassName,
     private val groupPackage: String,
+    private val generatePreview: Boolean
 ) {
     /**
      * Generates icons and writes them to [outputSrcDirectory], using [iconNamePredicate] to
@@ -60,7 +61,8 @@ class IconWriter(
             val (fileSpec, accessProperty) = VectorAssetGenerator(
                 iconName,
                 groupPackage,
-                vector
+                vector,
+                generatePreview
             ).createFileSpec(groupClass)
 
             fileSpec.writeTo(outputSrcDirectory)

src/main/kotlin/androidx/compose/material/icons/generator/Names.kt

@@ -24,10 +24,15 @@ import com.squareup.kotlinpoet.MemberName
  */
 enum class PackageNames(val packageName: String) {
     MaterialIconsPackage("androidx.compose.material.icons"),
-    GraphicsPackage("androidx.compose.ui.graphics"),
+    UiPackage("androidx.compose.ui"),
+    GraphicsPackage(UiPackage.packageName + ".graphics"),
     VectorPackage(GraphicsPackage.packageName + ".vector"),
-    GeometryPackage("androidx.compose.ui.geometry"),
-    Unit("androidx.compose.ui.unit"),
+    GeometryPackage(UiPackage.packageName + ".geometry"),
+    Unit(UiPackage.packageName + ".unit"),
+    FoundationPackage("androidx.compose.foundation"),
+    LayoutPackage(FoundationPackage.packageName + ".layout"),
+    PreviewPackage(UiPackage.packageName + ".tooling.preview"),
+    RuntimePackage("androidx.compose.runtime"),
 }
 
 /**
@@ -40,6 +45,8 @@ object ClassNames {
     val StrokeCap = PackageNames.GraphicsPackage.className("StrokeCap", CompanionImportName)
     val StrokeJoin = PackageNames.GraphicsPackage.className("StrokeJoin", CompanionImportName)
     val Brush = PackageNames.GraphicsPackage.className("Brush", CompanionImportName)
+    val Preview = PackageNames.PreviewPackage.className("Preview")
+    val Composable = PackageNames.RuntimePackage.className("Composable")
 }
 
 /**

src/main/kotlin/androidx/compose/material/icons/generator/VectorAssetGenerator.kt

@@ -38,11 +38,13 @@ data class VectorAssetGenerationResult(
  * @param iconTheme the theme that this vector belongs to. Used to scope the property to the
  * correct receiver object, and also for the package name of the generated file.
  * @param vector the parsed vector to generate VectorAssetBuilder commands for
+ * @param generatePreview if true a preview for the icon will be created.
  */
 class VectorAssetGenerator(
     private val iconName: String,
     private val iconGroupPackage: String,
-    private val vector: Vector
+    private val vector: Vector,
+    private val generatePreview: Boolean
 ) {
     /**
      * @return a [FileSpec] representing a Kotlin source file containing the property for this
@@ -70,7 +72,9 @@ class VectorAssetGenerator(
                 .build()
         ).addProperty(
             backingProperty
-        ).setIndent().build()
+        )
+            .apply { if (generatePreview) addFunction(iconPreview(MemberName(groupClassName, iconName))) }
+            .setIndent().build()
 
         return VectorAssetGenerationResult(generation, iconName)
     }
@@ -116,7 +120,40 @@ class VectorAssetGenerator(
             .build()
     }
 
+    /**
+     * @param iconName Name that will be used to call the Icon inside the preview.
+     *
+     * Example:
+     * ```kotlin
+     *   @Preview
+     *   @Composable
+     *   private fun Preview(): Unit {
+     *      Box(modifier = Modifier.padding(12.dp)) {
+     *          Image(imageVector = Icon.Foo, contentDescription = "")
+     *      }
+     *   }
+     * ```
+     */
+    private fun iconPreview(iconName: MemberName): FunSpec {
+        val previewAnnotation = AnnotationSpec.builder(ClassNames.Preview).build()
+        val composableAnnotation = AnnotationSpec.builder(ClassNames.Composable).build()
+        val box = MemberName(PackageNames.LayoutPackage.packageName, "Box")
+        val modifier = MemberName(PackageNames.UiPackage.packageName, "Modifier")
+        val padding = MemberName(PackageNames.LayoutPackage.packageName, "padding")
+        val paddingValue = MemberNames.Dp
+        val composeImage = MemberName(PackageNames.FoundationPackage.packageName, "Image")
 
+        return FunSpec.builder("Preview")
+            .addModifiers(KModifier.PRIVATE)
+            .addAnnotation(previewAnnotation)
+            .addAnnotation(composableAnnotation)
+            .addCode(buildCodeBlock {
+                beginControlFlow("%M(modifier = %M.%M(12.%M))", box, modifier, padding, paddingValue)
+                addStatement("%M(imageVector = %M, contentDescription = \"\")", composeImage, iconName)
+                endControlFlow()
+            })
+            .build()
+    }
 }
 
 /**

src/main/kotlin/br/com/devsrsouza/svg2compose/Svg2Compose.kt

@@ -27,7 +27,8 @@ object Svg2Compose {
         vectorsDirectory: File,
         type: VectorType = VectorType.SVG,
         iconNameTransformer: IconNameTransformer = { it, _ -> it },
-        allAssetsPropertyName: String = "AllAssets"
+        allAssetsPropertyName: String = "AllAssets",
+        generatePreview: Boolean = true,
     ): ParsingResult {
         fun nameRelative(vectorFile: File) = vectorFile.relativeTo(vectorsDirectory).path
 

src/test/kotlin/EmojiTest.kt

@@ -16,6 +16,7 @@ fun main(){
         iconNameTransformer = { name, group ->
             name.split("-").joinToString(separator = "").removePrefix(group)
         },
-        allAssetsPropertyName = "AllIcons"
+        allAssetsPropertyName = "AllIcons",
+        generatePreview = true,
     )
 }