Theoretically become no_std compatible (#2)

This commit adds no_std compliance and some trybuild tests to verify the no_std compliance and a ci configuration for github actions to verify said compliance.

Author: yaahc

.github/workflows/ci.yml

@@ -0,0 +1,81 @@
+on: [push]
+
+name: Continuous integration
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - 1.31.0
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
+
+  test:
+    name: Test Suite
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - nightly
+          - 1.31.0
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - 1.31.0
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          override: true
+      - run: rustup component add rustfmt
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - stable
+          - 1.31.0
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{ matrix.rust }}
+          override: true
+      - run: rustup component add clippy
+      - uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: -- -D warnings

.github/workflows/rust.yml

@@ -22,3 +22,9 @@ proc-macro = true
 syn = "1.0"
 quote = "1.0"
 proc-macro2 = "1.0"
+
+[dev-dependencies]
+trybuild = "1.0"
+static_assertions = "0.3.4"
+libc = { version = "0.2", default-features = false }
+rustversion = "1.0.0"

Cargo.toml

@@ -28,8 +28,8 @@ fn impl_struct(input: &DeriveInput, data: &DataStruct) -> Result<TokenStream> {
             Fields::Unit => quote!(_),
         };
         quote! {
-            impl #impl_generics std::fmt::Display for #ty #ty_generics #where_clause {
-                fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+            impl #impl_generics core::fmt::Display for #ty #ty_generics #where_clause {
+                fn fmt(&self, formatter: &mut core::fmt::Formatter) -> core::fmt::Result {
                     #[allow(unused_variables)]
                     let #pat = self;
                     #display
@@ -76,8 +76,8 @@ fn impl_enum(input: &DeriveInput, data: &DataEnum) -> Result<TokenStream> {
             })
             .collect::<Result<Vec<_>>>()?;
         Some(quote! {
-            impl #impl_generics std::fmt::Display for #ty #ty_generics #where_clause {
-                fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+            impl #impl_generics core::fmt::Display for #ty #ty_generics #where_clause {
+                fn fmt(&self, formatter: &mut core::fmt::Formatter) -> core::fmt::Result {
                     #[allow(unused_variables)]
                     match self {
                         #(#arms,)*

src/expand.rs

@@ -0,0 +1,7 @@
+#[rustversion::attr(not(nightly), ignore)]
+#[test]
+fn no_std() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/no_std/without.rs");
+    t.pass("tests/no_std/with.rs");
+}

tests/compile_tests.rs

@@ -0,0 +1,26 @@
+#![feature(lang_items, start)]
+#![no_std]
+
+#[start]
+fn start(_argc: isize, _argv: *const *const u8) -> isize {
+    0
+}
+
+#[lang = "eh_personality"]
+#[no_mangle]
+pub extern "C" fn rust_eh_personality() {}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    unsafe {
+        libc::abort();
+    }
+}
+
+use displaydoc::Display;
+
+/// this type is pretty swell
+#[derive(Display)]
+struct FakeType;
+
+static_assertions::assert_impl_all!(label; FakeType, core::fmt::Display);

tests/no_std/with.rs

@@ -0,0 +1,25 @@
+#![feature(lang_items, start)]
+#![no_std]
+
+#[start]
+fn start(_argc: isize, _argv: *const *const u8) -> isize {
+    0
+}
+
+#[lang = "eh_personality"]
+#[no_mangle]
+pub extern "C" fn rust_eh_personality() {}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    unsafe {
+        libc::abort();
+    }
+}
+
+use displaydoc::Display;
+
+/// this type is pretty swell
+struct FakeType;
+
+static_assertions::assert_impl_all!(label; FakeType, core::fmt::Display);

tests/no_std/without.rs

@@ -0,0 +1,20 @@
+warning: unused import: `displaydoc::Display`
+  --> $DIR/without.rs:20:5
+   |
+20 | use displaydoc::Display;
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(unused_imports)]` on by default
+
+error[E0277]: `FakeType` doesn't implement `core::fmt::Display`
+  --> $DIR/without.rs:25:44
+   |
+25 | static_assertions::assert_impl_all!(label; FakeType, core::fmt::Display);
+   | -------------------------------------------^^^^^^^^----------------------
+   | |                                          |
+   | |                                          `FakeType` cannot be formatted with the default formatter
+   | required by this bound in `label::assert_impl_all`
+   |
+   = help: the trait `core::fmt::Display` is not implemented for `FakeType`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)