Add stress test with 2^16 variants (#90)

This is very slow to compile, but should not crash the compiler (as it did before #89)

Closes #83

.github/workflows/presubmit.yml

@@ -59,6 +59,12 @@ jobs:
           command: build
           args: --manifest-path=serde_example/Cargo.toml --target thumbv6m-none-eabi -p serde_example --lib --no-default-features
           toolchain: ${{ matrix.toolchain }}
+      - name: Regression test for https://github.com/illicitonion/num_enum/issues/83
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --manifest-path=stress_tests/Cargo.toml
+          toolchain: ${{ matrix.toolchain }}
       - name: Doc
         uses: actions-rs/cargo@v1
         with:

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["num_enum", "num_enum_derive", "renamed_num_enum", "serde_example"]
+members = ["num_enum", "num_enum_derive", "renamed_num_enum", "serde_example", "stress_tests"]
 # Exclude num_enum_derive because its useful doc comments import num_enum, which the crate doesn't do (because it would
 # cause a circular dependency), so the doc tests don't actually compile.
-default-members  = ["num_enum", "renamed_num_enum", "serde_example"]
+default-members  = ["num_enum", "renamed_num_enum", "serde_example", "stress_tests"]

num_enum/tests/try_build/compile_fail/exhaustive_enum.stderr

@@ -1,4 +1,4 @@
-error: #[derive(FromPrimitive)] requires a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`
+error: #[derive(num_enum::FromPrimitive)] requires enum to be exhaustive, or a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`
  --> $DIR/exhaustive_enum.rs:1:10
   |
 1 | #[derive(num_enum::FromPrimitive)]

num_enum/tests/try_build/compile_fail/missing_default.stderr

@@ -1,4 +1,4 @@
-error: #[derive(FromPrimitive)] requires a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`
+error: #[derive(num_enum::FromPrimitive)] requires enum to be exhaustive, or a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`
  --> $DIR/missing_default.rs:1:10
   |
 1 | #[derive(num_enum::FromPrimitive)]

num_enum_derive/src/lib.rs

@@ -179,6 +179,23 @@ struct EnumInfo {
 }
 
 impl EnumInfo {
+    /// Returns whether the number of variants (ignoring defaults, catch-alls, etc) is the same as
+    /// the capacity of the repr.
+    fn is_naturally_exhaustive(&self) -> Result<bool> {
+        let repr_str = self.repr.to_string();
+        if !repr_str.is_empty() {
+            let suffix = repr_str
+                .strip_prefix('i')
+                .or_else(|| repr_str.strip_prefix('u'));
+            if let Some(suffix) = suffix {
+                if let Ok(bits) = suffix.parse::<u8>() {
+                    return Ok(1 << bits == self.variants.len());
+                }
+            }
+        }
+        die!(self.repr.clone() => "Failed to parse repr into bit size");
+    }
+
     fn has_default_variant(&self) -> bool {
         self.default().is_some()
     }
@@ -563,15 +580,25 @@ pub fn derive_from_primitive(input: TokenStream) -> TokenStream {
     let enum_info: EnumInfo = parse_macro_input!(input);
     let krate = Ident::new(&get_crate_name(), Span::call_site());
 
-    let catch_all_body = if let Some(default_ident) = enum_info.default() {
-        quote! { Self::#default_ident }
-    } else if let Some(catch_all_ident) = enum_info.catch_all() {
-        quote! { Self::#catch_all_ident(number) }
-    } else {
-        let span = Span::call_site();
-        let message =
-            "#[derive(FromPrimitive)] requires a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`";
-        return syn::Error::new(span, message).to_compile_error().into();
+    let is_naturally_exhaustive = enum_info.is_naturally_exhaustive();
+    let catch_all_body = match is_naturally_exhaustive {
+        Ok(is_naturally_exhaustive) => {
+            if is_naturally_exhaustive {
+                quote! { unreachable!("exhaustive enum") }
+            } else if let Some(default_ident) = enum_info.default() {
+                quote! { Self::#default_ident }
+            } else if let Some(catch_all_ident) = enum_info.catch_all() {
+                quote! { Self::#catch_all_ident(number) }
+            } else {
+                let span = Span::call_site();
+                let message =
+                    "#[derive(num_enum::FromPrimitive)] requires enum to be exhaustive, or a variant marked with `#[default]`, `#[num_enum(default)]`, or `#[num_enum(catch_all)`";
+                return syn::Error::new(span, message).to_compile_error().into();
+            }
+        }
+        Err(err) => {
+            return err.to_compile_error().into();
+        }
     };
 
     let EnumInfo {
@@ -881,7 +908,7 @@ pub fn derive_default(stream: TokenStream) -> TokenStream {
         None => {
             let span = Span::call_site();
             let message =
-                "#[derive(num_enum::Default)] requires a variant marked with `#[default]` or `#[num_enum(default)]`";
+                "#[derive(num_enum::Default)] requires enum to be exhaustive, or a variant marked with `#[default]` or `#[num_enum(default)]`";
             return syn::Error::new(span, message).to_compile_error().into();
         }
     };

stress_tests/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "stress_tests"
+version = "0.1.0"
+authors = [
+  "Daniel Wagner-Hall <[email protected]>",
+  "Daniel Henry-Mantilla <[email protected]>",
+  "Vincent Esche <[email protected]>",
+]
+description = "Tests using large enums. Regression test for https://github.com/illicitonion/num_enum/issues/83."
+edition = "2018"
+repository = "https://github.com/illicitonion/num_enum"
+publish = false
+
+[dev-dependencies]
+num_enum = { path = "../num_enum" }
+trybuild = "1.0.31"

stress_tests/tests/stress_test.rs

@@ -0,0 +1,7 @@
+use std::path::Path;
+
+#[test]
+fn stress_test() {
+    let pass = trybuild::TestCases::new();
+    pass.pass(Path::new("tests/stress_tests/*.rs"));
+}