repl: Create dumy Wasm implementations of SystemTime and Duration

compiler/load/src/file.rs

@@ -43,9 +43,13 @@ use std::iter;
 use std::path::{Path, PathBuf};
 use std::str::from_utf8_unchecked;
 use std::sync::Arc;
-use std::time::{Duration, SystemTime};
 use std::{env, fs};
 
+#[cfg(not(target_family = "wasm"))]
+use std::time::{Duration, SystemTime};
+#[cfg(target_family = "wasm")]
+use wasm_system_time::{Duration, SystemTime};
+
 /// Default name for the binary generated for an app, if an invalid one was specified.
 const DEFAULT_APP_OUTPUT_PATH: &str = "app";
 

compiler/load/src/lib.rs

@@ -3,3 +3,6 @@
 #![allow(clippy::large_enum_variant)]
 pub mod docs;
 pub mod file;
+
+#[cfg(target_family = "wasm")]
+mod wasm_system_time;

compiler/load/src/wasm_system_time.rs

@@ -0,0 +1,42 @@
+#![cfg(target_family = "wasm")]
+/*
+For the Web REPL (repl_www), we build the compiler as a Wasm module.
+SystemTime is the only thing in the compiler that would need a special implementation for this.
+There is a WASI implementation for it, but we are targeting the browser, not WASI!
+It's possible to write browser versions of WASI's low-level ABI but we'd rather avoid it.
+Instead we use these dummy implementations, which should just disappear at compile time.
+*/
+
+#[derive(Debug, Clone, Copy)]
+pub struct SystemTime;
+
+impl SystemTime {
+    fn now() -> Self {
+        SystemTime
+    }
+    fn duration_since(&self, _: SystemTime) -> Result<Duration, String> {
+        Ok(Duration)
+    }
+    fn elapsed(&self) -> Result<Duration, String> {
+        Ok(Duration)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Duration;
+
+impl Duration {
+    fn checked_sub(&self, _: Duration) -> Option<Duration> {
+        Some(Duration)
+    }
+}
+
+impl Default for Duration {
+    fn default() -> Self {
+        Duration
+    }
+}
+
+impl std::ops::AddAssign for Duration {
+    fn add_assign(&mut self, _: Duration) {}
+}