Allow preconfiguring WASMER_DIR at build time

lib/cli/Cargo.toml

@@ -10,6 +10,7 @@ license = "MIT"
 readme = "README.md"
 edition = "2018"
 default-run = "wasmer"
+build = "build.rs"
 
 [[bin]]
 name = "wasmer"

lib/cli/build.rs

@@ -0,0 +1,4 @@
+pub fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-env-changed=WASMER_INSTALL_PREFIX");
+}

lib/cli/src/commands/config.rs

@@ -45,10 +45,16 @@ impl Config {
     }
     fn inner_execute(&self) -> Result<()> {
         let key = "WASMER_DIR";
-        let wasmer_dir = env::var(key).context(format!(
+        let wasmer_dir = env::var(key)
-            "failed to retrieve the {} environment variables",
+            .or_else(|e| {
-            key
+                option_env!("WASMER_INSTALL_PREFIX")
-        ))?;
+                    .map(str::to_string)
+                    .ok_or(e)
+            })
+            .context(format!(
+                "failed to retrieve the {} environment variables",
+                key
+            ))?;
 
         let prefix = PathBuf::from(wasmer_dir);
 

lib/cli/src/commands/create_exe.rs

@@ -155,7 +155,13 @@ fn generate_header(header_file_src: &[u8]) -> anyhow::Result<()> {
 
 fn get_wasmer_dir() -> anyhow::Result<PathBuf> {
     Ok(PathBuf::from(
-        env::var("WASMER_DIR").context("Trying to read env var `WASMER_DIR`")?,
+        env::var("WASMER_DIR")
+            .or_else(|e| {
+                option_env!("WASMER_INSTALL_PREFIX")
+                    .map(str::to_string)
+                    .ok_or(e)
+            })
+            .context("Trying to read env var `WASMER_DIR`")?,
     ))
 }