Support specifying ranges of alternate values

For simplicity, we require both ends of the range to be specified an
literals.

This only works if the `complex-expressions` feature is enabled, as
`syn` can't parse ranges without its `full` feature being enabled, which
significantly increases compile times. We give a useful error if you
attempt to use ranges without this feature being enabled.

num_enum/tests/from_primitive.rs

@@ -115,3 +115,30 @@ fn from_primitive_number_catch_all() {
     let two = Enum::from_primitive(2_u8);
     assert_eq!(two, Enum::NonZero(2_u8));
 }
+
+#[cfg(feature = "complex-expressions")]
+#[test]
+fn from_primitive_number_with_inclusive_range() {
+    #[derive(Debug, Eq, PartialEq, FromPrimitive)]
+    #[repr(u8)]
+    enum Enum {
+        Zero = 0,
+        #[num_enum(alternatives = [2..=255])]
+        NonZero,
+    }
+
+    let zero = Enum::from_primitive(0_u8);
+    assert_eq!(zero, Enum::Zero);
+
+    let one = Enum::from_primitive(1_u8);
+    assert_eq!(one, Enum::NonZero);
+
+    let two = Enum::from_primitive(2_u8);
+    assert_eq!(two, Enum::NonZero);
+
+    let three = Enum::from_primitive(3_u8);
+    assert_eq!(three, Enum::NonZero);
+
+    let twofivefive = Enum::from_primitive(255_u8);
+    assert_eq!(twofivefive, Enum::NonZero);
+}

num_enum/tests/try_build.rs

@@ -8,14 +8,42 @@ fn trybuild() {
 
     let mut _renamer = None;
 
+    let compile_fail_dir = directory.join("compile_fail");
+
     // Sometimes error messages change on beta/nightly - allow alternate errors on those.
-    _renamer = Some(Renamer::rename(directory.join("compile_fail")).unwrap());
+    _renamer = Some(Renamer::rename(compile_fail_dir.clone()).unwrap());
 
     let fail = trybuild::TestCases::new();
-    fail.compile_fail(directory.join("compile_fail/*.rs"));
+    fail.compile_fail(compile_fail_dir.join("*.rs"));
+    add_feature_dirs(&compile_fail_dir, &fail, ExpectedResult::Fail);
 
     let pass = trybuild::TestCases::new();
-    pass.pass(directory.join("pass/*.rs"));
+    let pass_dir = directory.join("pass");
+    pass.pass(pass_dir.join("*.rs"));
+    add_feature_dirs(&pass_dir, &pass, ExpectedResult::Pass);
+}
+
+enum ExpectedResult {
+    Pass,
+    Fail,
+}
+
+fn add_feature_dirs(
+    parent_dir: &Path,
+    test_cases: &trybuild::TestCases,
+    expected_result: ExpectedResult,
+) {
+    let features_dir = parent_dir.join("features");
+    let feature_specific_dir = if cfg!(feature = "complex-expressions") {
+        features_dir.join("complex-expressions")
+    } else {
+        features_dir.join("!complex-expressions")
+    };
+    let tests = feature_specific_dir.join("*.rs");
+    match expected_result {
+        ExpectedResult::Pass => test_cases.pass(tests),
+        ExpectedResult::Fail => test_cases.compile_fail(tests),
+    }
 }
 
 struct Renamer(Vec<PathBuf>);

num_enum/tests/try_build/compile_fail/features/!complex-expressions/alternate_exprs_with_range.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::FromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [2..=255])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/!complex-expressions/alternate_exprs_with_range.stderr

@@ -0,0 +1,5 @@
+error: Ranges are only supported as num_enum alternate values if the `complex-expressions` feature of the crate `num_enum` is enabled
+ --> tests/try_build/compile_fail/features/!complex-expressions/alternate_exprs_with_range.rs:5:32
+  |
+5 |     #[num_enum(alternatives = [2..=255])]
+  |                                ^^^^^^^

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_lower_bound.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [..255])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_lower_bound.stderr

@@ -0,0 +1,5 @@
+error: When ranges are used for alternate values, both bounds most be explicitly specified numeric literals
+ --> tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_lower_bound.rs:5:32
+  |
+5 |     #[num_enum(alternatives = [..255])]
+  |                                ^^^^^

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_upper_bound.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [2..])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_upper_bound.stderr

@@ -0,0 +1,5 @@
+error: When ranges are used for alternate values, both bounds most be explicitly specified numeric literals
+ --> tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_missing_upper_bound.rs:5:32
+  |
+5 |     #[num_enum(alternatives = [2..])]
+  |                                ^^^

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_lower_bound.rs

@@ -0,0 +1,13 @@
+const TWO: u8 = 2;
+
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [TWO..=255])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_lower_bound.stderr

@@ -0,0 +1,5 @@
+error: When ranges are used for alternate values, both bounds most be explicitly specified numeric literals
+ --> tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_lower_bound.rs:7:32
+  |
+7 |     #[num_enum(alternatives = [TWO..=255])]
+  |                                ^^^^^^^^^

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_upper_bound.rs

@@ -0,0 +1,13 @@
+const TWOFIVEFIVE: u8 = 255;
+
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [2..=TWOFIVEFIVE])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_upper_bound.stderr

@@ -0,0 +1,5 @@
+error: When ranges are used for alternate values, both bounds most be explicitly specified numeric literals
+ --> tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_nonlit_upper_bound.rs:7:32
+  |
+7 |     #[num_enum(alternatives = [2..=TWOFIVEFIVE])]
+  |                                ^^^^^^^^^^^^^^^

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_swapped_bounds.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [255..=2])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_swapped_bounds.stderr

@@ -0,0 +1,5 @@
+error: When using ranges for alternate values, upper bound must not be less than lower bound
+ --> tests/try_build/compile_fail/features/complex-expressions/alternate_exprs_range_swapped_bounds.rs:5:32
+  |
+5 |     #[num_enum(alternatives = [255..=2])]
+  |                                ^^^^^^^

num_enum/tests/try_build/pass/exhaustive_enum_try_from.rs

@@ -0,0 +1,40 @@
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum ExhaustiveTryFrom {
+    #[num_enum(alternatives = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15])]
+    A = 0,
+    #[num_enum(alternatives = [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31])]
+    B = 16,
+    #[num_enum(alternatives = [33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47])]
+    C = 32,
+    #[num_enum(alternatives = [49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63])]
+    D = 48,
+    #[num_enum(alternatives = [65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79])]
+    E = 64,
+    #[num_enum(alternatives = [81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95])]
+    F = 80,
+    #[num_enum(alternatives = [97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111])]
+    G = 96,
+    #[num_enum(alternatives = [113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127])]
+    H = 112,
+    #[num_enum(alternatives = [129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143])]
+    I = 128,
+    #[num_enum(alternatives = [145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159])]
+    J = 144,
+    #[num_enum(alternatives = [161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175])]
+    K = 160,
+    #[num_enum(alternatives = [177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191])]
+    L = 176,
+    #[num_enum(alternatives = [193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207])]
+    M = 192,
+    #[num_enum(alternatives = [209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223])]
+    N = 208,
+    #[num_enum(alternatives = [225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239])]
+    O = 224,
+    #[num_enum(alternatives = [241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255])]
+    P = 240,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/pass/exhaustive_enum_via_default.rs

@@ -0,0 +1,39 @@
+#[derive(num_enum::FromPrimitive)]
+#[repr(u8)]
+enum ExhaustiveFrom {
+    #[num_enum(default)]
+    #[num_enum(alternatives = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15])]
+    A = 0,
+    #[num_enum(alternatives = [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31])]
+    B = 16,
+    #[num_enum(alternatives = [33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47])]
+    C = 32,
+    #[num_enum(alternatives = [49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63])]
+    D = 48,
+    #[num_enum(alternatives = [65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79])]
+    E = 64,
+    #[num_enum(alternatives = [81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95])]
+    F = 80,
+    #[num_enum(alternatives = [97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111])]
+    G = 96,
+    #[num_enum(alternatives = [113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127])]
+    H = 112,
+    #[num_enum(alternatives = [129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143])]
+    I = 128,
+    #[num_enum(alternatives = [145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159])]
+    J = 144,
+    #[num_enum(alternatives = [161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175])]
+    K = 160,
+    #[num_enum(alternatives = [177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191])]
+    L = 176,
+    #[num_enum(alternatives = [193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207])]
+    M = 192,
+    #[num_enum(alternatives = [209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223])]
+    N = 208,
+    #[num_enum(alternatives = [225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239])]
+    O = 224,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/pass/features/complex-expressions/alternate_exprs_exhaustive_with_range.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::FromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [2..=255])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}

num_enum/tests/try_build/pass/features/complex-expressions/alternate_exprs_non_exhaustive_with_range.rs

@@ -0,0 +1,11 @@
+#[derive(num_enum::TryFromPrimitive)]
+#[repr(u8)]
+enum Numbers {
+    Zero = 0,
+    #[num_enum(alternatives = [2..255])]
+    NonZero = 1,
+}
+
+fn main() {
+
+}