Set up dummy build script for docs.rs

Docs.rs has no network access, so we can't `cargo install` the binary dependencies. This is not required for doc generation, so we trick our way around that issue by providing a dummy build script just for docs.rs.

Author: phil-opp

Diff for: Cargo.toml

@@ -105,7 +105,7 @@ rustflags = [
 llvm-tools = "0.1.1"
 
 [package.metadata.docs.rs]
-default-target = "x86_64-unknown-linux-gnu"
+rustc-args = ["--cfg", "docsrs_dummy_build"]
 
 [package.metadata.release]
 dev-version = false

Diff for: build.rs

@@ -46,6 +46,7 @@ fn main() {
     );
 }
 
+#[cfg(not(docsrs_dummy_build))]
 fn build_uefi_bootloader(out_dir: &Path) -> PathBuf {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
@@ -79,6 +80,7 @@ fn build_uefi_bootloader(out_dir: &Path) -> PathBuf {
     }
 }
 
+#[cfg(not(docsrs_dummy_build))]
 fn build_bios_boot_sector(out_dir: &Path) -> PathBuf {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
@@ -121,6 +123,7 @@ fn build_bios_boot_sector(out_dir: &Path) -> PathBuf {
     convert_elf_to_bin(elf_path)
 }
 
+#[cfg(not(docsrs_dummy_build))]
 fn build_bios_stage_2(out_dir: &Path) -> PathBuf {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
@@ -161,6 +164,7 @@ fn build_bios_stage_2(out_dir: &Path) -> PathBuf {
     convert_elf_to_bin(elf_path)
 }
 
+#[cfg(not(docsrs_dummy_build))]
 fn build_bios_stage_3(out_dir: &Path) -> PathBuf {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
@@ -201,6 +205,7 @@ fn build_bios_stage_3(out_dir: &Path) -> PathBuf {
     convert_elf_to_bin(elf_path)
 }
 
+#[cfg(not(docsrs_dummy_build))]
 fn build_bios_stage_4(out_dir: &Path) -> PathBuf {
     let cargo = std::env::var("CARGO").unwrap_or_else(|_| "cargo".into());
     let mut cmd = Command::new(cargo);
@@ -268,3 +273,26 @@ fn convert_elf_to_bin(elf_path: PathBuf) -> PathBuf {
     }
     flat_binary_path
 }
+
+// dummy implementations because docsrs builds have no network access
+
+#[cfg(docsrs_dummy_build)]
+fn build_uefi_bootloader(_out_dir: &Path) -> PathBuf {
+    PathBuf::new()
+}
+#[cfg(docsrs_dummy_build)]
+fn build_bios_boot_sector(_out_dir: &Path) -> PathBuf {
+    PathBuf::new()
+}
+#[cfg(docsrs_dummy_build)]
+fn build_bios_stage_2(_out_dir: &Path) -> PathBuf {
+    PathBuf::new()
+}
+#[cfg(docsrs_dummy_build)]
+fn build_bios_stage_3(_out_dir: &Path) -> PathBuf {
+    PathBuf::new()
+}
+#[cfg(docsrs_dummy_build)]
+fn build_bios_stage_4(_out_dir: &Path) -> PathBuf {
+    PathBuf::new()
+}