Merge source code from aspnet/Configuration into this repo

\n\nCommit migrated from dotnet/extensions@8a9b64a

Author: Nate McMaster

src/Configuration.KeyPerFile/Directory.Build.props

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+<Project>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory)..\, Directory.Build.props))\Directory.Build.props" />
+
+  <PropertyGroup>
+    <GenerateDocumentationFile Condition=" '$(IsTestProject)' != 'true' AND '$(IsSampleProject)' != 'true' ">true</GenerateDocumentationFile>
+    <PackageTags>configuration</PackageTags>
+  </PropertyGroup>
+</Project>

src/Configuration.KeyPerFile/src/KeyPerFileConfigurationBuilderExtensions.cs

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+using System;
+using System.IO;
+using Microsoft.Extensions.Configuration.KeyPerFile;
+using Microsoft.Extensions.FileProviders;
+
+namespace Microsoft.Extensions.Configuration
+{
+    /// <summary>
+    /// Extension methods for registering <see cref="KeyPerFileConfigurationProvider"/> with <see cref="IConfigurationBuilder"/>.
+    /// </summary>
+    public static class KeyPerFileConfigurationBuilderExtensions
+    {
+        /// <summary>
+        /// Adds configuration using files from a directory. File names are used as the key,
+        /// file contents are used as the value.
+        /// </summary>
+        /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>
+        /// <param name="directoryPath">The path to the directory.</param>
+        /// <param name="optional">Whether the directory is optional.</param>
+        /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
+        public static IConfigurationBuilder AddKeyPerFile(this IConfigurationBuilder builder, string directoryPath, bool optional)
+            => builder.AddKeyPerFile(source =>
+            {
+                // Only try to set the file provider if its not optional or the directory exists 
+                if (!optional || Directory.Exists(directoryPath))
+                {
+                    source.FileProvider = new PhysicalFileProvider(directoryPath);
+                }
+                source.Optional = optional;
+            });
+
+        /// <summary>
+        /// Adds configuration using files from a directory. File names are used as the key,
+        /// file contents are used as the value.
+        /// </summary>
+        /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>
+        /// <param name="configureSource">Configures the source.</param>
+        /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
+        public static IConfigurationBuilder AddKeyPerFile(this IConfigurationBuilder builder, Action<KeyPerFileConfigurationSource> configureSource)
+            => builder.Add(configureSource);
+    }
+}

src/Configuration.KeyPerFile/src/KeyPerFileConfigurationProvider.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Microsoft.Extensions.Configuration.KeyPerFile
+{
+    /// <summary>
+    /// A <see cref="ConfigurationProvider"/> that uses a directory's files as configuration key/values.
+    /// </summary>
+    public class KeyPerFileConfigurationProvider : ConfigurationProvider
+    {
+        KeyPerFileConfigurationSource Source { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance.
+        /// </summary>
+        /// <param name="source">The settings.</param>
+        public KeyPerFileConfigurationProvider(KeyPerFileConfigurationSource source)
+            => Source = source ?? throw new ArgumentNullException(nameof(source));
+
+        private static string NormalizeKey(string key)
+            => key.Replace("__", ConfigurationPath.KeyDelimiter);
+
+        private static string TrimNewLine(string value)
+            => value.EndsWith(Environment.NewLine)
+                ? value.Substring(0, value.Length - Environment.NewLine.Length)
+                : value;
+
+        /// <summary>
+        /// Loads the docker secrets.
+        /// </summary>
+        public override void Load()
+        {
+            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+
+            if (Source.FileProvider == null)
+            {
+                if (Source.Optional)
+                {
+                    return;
+                }
+                else
+                {
+                    throw new DirectoryNotFoundException("A non-null file provider for the directory is required when this source is not optional.");
+                }
+            }
+
+            var directory = Source.FileProvider.GetDirectoryContents("/");
+            if (!directory.Exists && !Source.Optional)
+            {
+                throw new DirectoryNotFoundException("The root directory for the FileProvider doesn't exist and is not optional.");
+            }
+
+            foreach (var file in directory)
+            {
+                if (file.IsDirectory)
+                {
+                    continue;
+                }
+
+                using (var stream = file.CreateReadStream())
+                using (var streamReader = new StreamReader(stream))
+                {
+                    if (Source.IgnoreCondition == null || !Source.IgnoreCondition(file.Name))
+                    {
+                        Data.Add(NormalizeKey(file.Name), TrimNewLine(streamReader.ReadToEnd()));
+                    }
+                }
+            }
+        }
+    }
+}

src/Configuration.KeyPerFile/src/KeyPerFileConfigurationSource.cs

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+using System;
+using System.IO;
+using Microsoft.Extensions.FileProviders;
+
+namespace Microsoft.Extensions.Configuration.KeyPerFile
+{
+    /// <summary>
+    /// An <see cref="IConfigurationSource"/> used to configure <see cref="KeyPerFileConfigurationProvider"/>.
+    /// </summary>
+    public class KeyPerFileConfigurationSource : IConfigurationSource
+    {
+        /// <summary>
+        /// Constructor;
+        /// </summary>
+        public KeyPerFileConfigurationSource()
+            => IgnoreCondition = s => IgnorePrefix != null && s.StartsWith(IgnorePrefix);
+
+        /// <summary>
+        /// The FileProvider whos root "/" directory files will be used as configuration data.
+        /// </summary>
+        public IFileProvider FileProvider { get; set; }
+
+        /// <summary>
+        /// Files that start with this prefix will be excluded.
+        /// Defaults to "ignore.".
+        /// </summary>
+        public string IgnorePrefix { get; set; } = "ignore.";
+
+        /// <summary>
+        /// Used to determine if a file should be ignored using its name.
+        /// Defaults to using the IgnorePrefix.
+        /// </summary>
+        public Func<string, bool> IgnoreCondition { get; set; }
+
+        /// <summary>
+        /// If false, will throw if the directory doesn't exist.
+        /// </summary>
+        public bool Optional { get; set; }
+
+        /// <summary>
+        /// Builds the <see cref="KeyPerFileConfigurationProvider"/> for this source.
+        /// </summary>
+        /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
+        /// <returns>A <see cref="KeyPerFileConfigurationProvider"/></returns>
+        public IConfigurationProvider Build(IConfigurationBuilder builder)
+            => new KeyPerFileConfigurationProvider(this);
+    }
+}

src/Configuration.KeyPerFile/src/Microsoft.Extensions.Configuration.KeyPerFile.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <Description>Configuration provider that uses files in a directory for Microsoft.Extensions.Configuration.</Description>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <EnableApiCheck>false</EnableApiCheck>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Reference Include="Microsoft.Extensions.Configuration" />
+    <Reference Include="Microsoft.Extensions.FileProviders.Physical" />
+  </ItemGroup>
+
+</Project>

src/Configuration.KeyPerFile/src/README.md

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+
+This is a configuration provider that uses a directory's files as data. A file's name is the key and the contents are the value.