TextLoader now checks for presence of source file with clear error message

src/Microsoft.ML.Core/ComponentModel/AssemblyLoadingUtils.cs

@@ -31,6 +31,10 @@ public static void LoadAndRegister(IHostEnvironment env, string[] assemblies)
                     {
                         // REVIEW: Will LoadFrom ever return null?
                         Contracts.CheckNonEmpty(path, nameof(path));
+                        if (!File.Exists(path))
+                        {
+                            throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+                        }
                         var assem = LoadAssembly(env, path);
                         if (assem != null)
                             continue;

src/Microsoft.ML.Data/DataLoadSave/Binary/BinaryLoaderSaverCatalog.cs

@@ -47,6 +47,10 @@ public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, IMult
         public static IDataView LoadFromBinary(this DataOperationsCatalog catalog, string path)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var env = catalog.GetEnvironment();
 

src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderSaverCatalog.cs

@@ -112,6 +112,10 @@ public static IDataView LoadFromTextFile(this DataOperationsCatalog catalog,
             bool allowSparse = TextLoader.Defaults.AllowSparse)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var options = new TextLoader.Options
             {
@@ -154,6 +158,10 @@ public static IDataView LoadFromTextFile<TInput>(this DataOperationsCatalog cata
             bool allowSparse = TextLoader.Defaults.AllowSparse)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             // REVIEW: it is almost always a mistake to have a 'trainable' text loader here.
             // Therefore, we are going to disallow data sample.
@@ -179,6 +187,10 @@ public static IDataView LoadFromTextFile(this DataOperationsCatalog catalog, str
             TextLoader.Options options = null)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var env = catalog.GetEnvironment();
             var source = new MultiFileSource(path);

src/Microsoft.ML.Transforms/SvmLight/SvmLightLoaderSaverCatalog.cs

@@ -65,6 +65,10 @@ public static IDataView LoadFromSvmLightFile(this DataOperationsCatalog catalog,
             bool zeroBased = false)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var file = new MultiFileSource(path);
             var loader = catalog.CreateSvmLightLoader(numberOfRows, inputSize, zeroBased, file);
@@ -83,6 +87,10 @@ public static IDataView LoadFromSvmLightFileWithFeatureNames(this DataOperations
             long? numberOfRows = null)
         {
             Contracts.CheckNonEmpty(path, nameof(path));
+            if (!File.Exists(path))
+            {
+                throw Contracts.ExceptParam(nameof(path), "File does not exist at path: {0}", path);
+            }
 
             var file = new MultiFileSource(path);
             var loader = catalog.CreateSvmLightLoaderWithFeatureNames(numberOfRows, file);

test/Microsoft.ML.Tests/TextLoaderTests.cs

@@ -142,20 +142,6 @@ public TextLoaderTests(ITestOutputHelper output)
             env = new ConsoleEnvironment(42).AddStandardComponents();
         }
 
-        [Fact]
-        public void ConstructorDoesntThrow()
-        {
-            var mlContext = new MLContext(seed: 1);
-
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt"));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt", hasHeader: true));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt", hasHeader: false));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt", hasHeader: false, trimWhitespace: false, allowSparse: false));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt", hasHeader: false, allowSparse: false));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<Input>("fakeFile.txt", hasHeader: false, allowQuoting: false));
-            Assert.NotNull(mlContext.Data.LoadFromTextFile<InputWithUnderscore>("fakeFile.txt"));
-        }
-
         [Fact]
         public void CanSuccessfullyApplyATransform()
         {
@@ -588,11 +574,11 @@ public void CanSuccessfullyTrimSpaces()
         }
 
         [Fact]
-        public void ThrowsExceptionWithPropertyName()
+        public void ThrowsExceptionWithMissingFile()
         {
             var mlContext = new MLContext(seed: 1);
-            var ex = Assert.Throws<InvalidOperationException>(() => mlContext.Data.LoadFromTextFile<ModelWithoutColumnAttribute>("fakefile.txt"));
-            Assert.StartsWith($"Field 'String1' is missing the {nameof(LoadColumnAttribute)} attribute", ex.Message);
+            var ex = Assert.Throws<ArgumentOutOfRangeException>(() => mlContext.Data.LoadFromTextFile<ModelWithoutColumnAttribute>("fakefile.txt"));
+            Assert.StartsWith("File does not exist at path: fakefile.txt", ex.Message);
         }
 
         [Fact]