fix binary/artifact-in-docker errors and uncertainties

.gitignore

@@ -1,4 +1,3 @@
 /target
 *.env
 .DS_Store
-web/styles.css

Dockerfile

@@ -7,6 +7,7 @@ ARG APP_NAME=arche
 FROM rust:${RUST_VERSION}-alpine AS build
 ARG APP_NAME
 WORKDIR /app
+ENV IN_DOCKER=true
 
 # Install host build dependencies.
 RUN apk add --no-cache clang lld musl-dev git
@@ -58,6 +59,7 @@ RUN adduser \
 RUN mkdir -p /app && chown appuser:appuser /app
 USER appuser
 WORKDIR /app
+ENV IN_DOCKER=true
 
 ENV DISCORD_BOT_TOKEN=""
 ENV DISCORD_SERVER_ID=""

build.rs

@@ -7,6 +7,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=web");
 
+    if std::env::var("IN_DOCKER").is_err() {
         let os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_else(|_| String::from("unknown"));
         let arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_else(|_| String::from("unknown"));
         let download_url = match (os.as_str(), arch.as_str()) {
@@ -27,10 +28,9 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         fs::create_dir_all(&out_dir)?;
 
         download_tailwind(&download_url, &tailwind_binary)?;
-
         println!("cargo:rustc-env=TAILWIND_BIN={}", tailwind_binary.display());
-
         run_tailwind(&tailwind_binary)?;
+    }
     Ok(())
 }
 

readme.txt

@@ -0,0 +1,8 @@
+arche
+=====
+
+Regarding /web/styles.css
+
+    The styles.css file, which is generated by a standalone Tailwind binary downloaded and executed automatically within build.rs, is to be committed any time it changes, as without it styling will be broken on the frontend part of the page.
+
+    This is in contrast to a perhaps expected approach of gitignoring them and just generating them every build; this is incompatible with building docker images in an efficient way, however, as docker exposes no way to mount directories while retaining ability to write files and execute binaries.