Make IntelliJ workaround compatible with 'run watch --crate' (#3355)

build/run.js

@@ -164,11 +164,8 @@ commands.build.rust = async function (argv) {
         args.push('--dev')
     }
     args.push('--')
-    // Enable source-file and line number information in the data generated by the `#[profile]`
-    // macro.
-    //
-    // The `profiler` library requires use of a Rust unstable feature, `proc_macro_span`, to be
-    // able to obtain this information.
+    // Enable a Rust unstable feature that the `#[profile]` macro uses to obtain source-file and line
+    // number information to include in generated profile files.
     //
     // The IntelliJ Rust plugin does not support the `proc_macro_span` Rust feature; using it causes
     // JetBrains IDEs to become entirely unaware of the items produced by `#[profile]`.
@@ -177,11 +174,17 @@ commands.build.rust = async function (argv) {
     // In order to have line number information in actual usage, but keep everything understandable
     // by JetBrains IDEs, we need IntelliJ/CLion to build crates differently from how they are
     // built for the application to be run. This is accomplished by gating the use of the unstable
-    // functionality by a Cargo feature. Cargo features are disabled by default, so when a Rust IDE
-    // builds crates internally in order to determine macro expansions, it will do so without line
-    // numbers. When this script is used to build the application, it is not for the purpose of IDE
-    // macro expansion, so we can safely enable line numbers.
-    args.push('--features=enso-profiler/line-numbers')
+    // functionality by a `cfg` flag. A `cfg` flag is disabled by default, so when a Rust IDE builds
+    // crates internally in order to determine macro expansions, it will do so without line numbers.
+    // When this script is used to build the application, it is not for the purpose of IDE macro
+    // expansion, so we can safely enable line numbers.
+    //
+    // The reason we don't use a Cargo feature for this is because this script can build different
+    // crates, and we'd like to enable this feature when building any crate that depends on the
+    // `profiler` crates. We cannot do something like '--feature=enso_profiler/line-numbers' without
+    // causing build to fail when building a crate that doesn't have `enso_profiler` in its
+    // dependency tree.
+    process.env.ENSO_ENABLE_PROC_MACRO_SPAN = 1
     await run_cargo('wasm-pack', args)
     await patch_file(paths.wasm.glue, js_workaround_patcher)
     await fs.rename(paths.wasm.mainRaw, paths.wasm.main)

lib/rust/profiler/Cargo.toml

@@ -13,6 +13,3 @@ enso-web = { path = "../web" }
 
 [dev-dependencies]
 futures = "0.3"
-
-[features]
-line-numbers = ["enso-profiler-macros/lineno"]

lib/rust/profiler/macros/Cargo.toml

@@ -12,6 +12,3 @@ proc-macro2 = "1.0"
 quote       = "1.0"
 syn         = { version = "1.0", features = [ "full", "visit-mut" ] }
 Inflector   = "0.11"
-
-[features]
-lineno      = []

lib/rust/profiler/macros/build.rs

@@ -1,7 +1,6 @@
-//! Build script for [`enso_profiler_macros`]. This is needed because `profiler_macros` has a
-//! profiling level controlled by the value of an environment variable at compile time, and cargo
-//! needs to be made aware that changes to the env can invalidate the result of compiling this
-//! crate and any dependents.
+//! Build script for [`enso_profiler_macros`]. This is needed to make cargo aware that
+//! the crate depends on the values of environment variables at compile time, and changes to those
+//! variables should result in recompiling this crate and its dependents.
 
 // === Non-Standard Linter Configuration ===
 #![warn(missing_copy_implementations)]
@@ -16,8 +15,23 @@
 
 
 fn main() {
-    println!("cargo:rerun-if-env-changed=ENSO_MAX_PROFILING_LEVEL");
+    declare_env_dependence("ENSO_MAX_PROFILING_LEVEL");
+    declare_env_cfg_flag("ENSO_ENABLE_PROC_MACRO_SPAN", "enso_enable=\"proc_macro_span\"");
+}
+
+/// Make cargo aware that the result of compiling this crate depends on an environment variable.
+fn declare_env_dependence(env: &str) {
+    println!("cargo:rerun-if-env-changed={}", env);
     // This is a no-op assignment, except it makes cargo aware that the output depends on the env.
-    let value = std::env::var("ENSO_MAX_PROFILING_LEVEL").unwrap_or_default();
-    println!("cargo:rustc-env=ENSO_MAX_PROFILING_LEVEL={}", value);
+    let value = std::env::var(env).unwrap_or_default();
+    println!("cargo:rustc-env={}={}", env, value);
+}
+
+/// Make cargo aware that the result of compiling this crate depends on an environment variable;
+/// convert that variable to a `cfg` flag so that it can be used for conditional compilation.
+fn declare_env_cfg_flag(env: &str, cfg: &str) {
+    println!("cargo:rerun-if-env-changed={}", env);
+    if std::env::var(env).is_ok() {
+        println!("cargo:rustc-cfg={}", cfg);
+    }
 }

lib/rust/profiler/macros/src/lib.rs

@@ -7,7 +7,7 @@
 //!   implementing this without proc macros would be complex and repetitious.
 //! - To implement the [`#[profile]`](macro@profile) attribute macro.
 
-#![cfg_attr(feature = "lineno", feature(proc_macro_span))]
+#![cfg_attr(enso_enable = "proc_macro_span", feature(proc_macro_span))]
 // === Standard Linter Configuration ===
 #![deny(non_ascii_idents)]
 #![warn(unsafe_code)]
@@ -290,13 +290,13 @@ pub fn profile(
     func.into_token_stream().into()
 }
 
-#[cfg(not(feature = "lineno"))]
+#[cfg(not(enso_enable = "proc_macro_span"))]
 /// Decorate the input with file:line info determined by the proc_macro's call site.
 fn make_label<L: fmt::Display>(name: L) -> String {
     format!("{} (?:?)", name)
 }
 
-#[cfg(feature = "lineno")]
+#[cfg(enso_enable = "proc_macro_span")]
 /// Decorate the input with file:line info determined by the proc_macro's call site.
 fn make_label<L: fmt::Display>(name: L) -> String {
     let span = proc_macro::Span::call_site();