From 4a0370290839a6ffe1907229de35b0d28f7fb4f7 Mon Sep 17 00:00:00 2001
From: dbr <dbr.onix@gmail.com>
Date: Tue, 2 Nov 2021 14:24:32 +1100
Subject: [PATCH] Use CARGO_FEATURE_x instead of #[cfg(...)]

Avoids unnecessary rebuilds of build script.

Also a few somewhat unrelated tidy-ups
---
 imgui-sys/build.rs | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/imgui-sys/build.rs b/imgui-sys/build.rs
index e3a56fe..9e01939 100644
--- a/imgui-sys/build.rs
+++ b/imgui-sys/build.rs
@@ -12,27 +12,19 @@ const DEFINES: &[(&str, Option<&str>)] = &[
     ("IMGUI_DISABLE_OSX_FUNCTIONS", None),
 ];
 
-fn assert_file_exists(path: &str) -> io::Result<()> {
-    match fs::metadata(path) {
-        Ok(_) => Ok(()),
-        Err(ref e) if e.kind() == io::ErrorKind::NotFound => {
-            panic!(
-                "Can't access {}. Did you forget to fetch git submodules?",
-                path
-            );
-        }
-        Err(e) => Err(e),
-    }
-}
-
 fn main() -> io::Result<()> {
     // Output define args for compiler
     for (key, value) in DEFINES.iter() {
         println!("cargo:DEFINE_{}={}", key, value.unwrap_or(""));
     }
 
+    // Feature flags - no extra dependencies, so these are queried as
+    // env-vars to avoid recompilation of build.rs
+    let docking_enabled = std::env::var_os("CARGO_FEATURE_DOCKING").is_some();
+    let wasm_enabled = std::env::var_os("CARGO_FEATURE_WASM").is_none();
+
     // If we aren't building WASM output, bunch of extra stuff to do
-    if std::env::var_os("CARGO_FEATURE_WASM").is_none() {
+    if !wasm_enabled {
         // C++ compiler
         let mut build = cc::Build::new();
         build.cpp(true);
@@ -45,26 +37,32 @@ fn main() -> io::Result<()> {
         // Freetype font rasterizer feature
         #[cfg(feature = "freetype")]
         {
+            // Find library
             let freetype = pkg_config::Config::new().find("freetype2").unwrap();
             for include in freetype.include_paths.iter() {
                 build.include(include);
             }
+            // Set flag for dear imgui
             build.define("IMGUI_ENABLE_FREETYPE", None);
             println!("cargo:DEFINE_IMGUI_ENABLE_FREETYPE=");
 
             // imgui_freetype.cpp needs access to `#include "imgui.h"`
             let manifest_dir = std::path::Path::new(env!("CARGO_MANIFEST_DIR"));
-            #[cfg(feature = "docking")]
-            build.include(manifest_dir.join("third-party/imgui-docking/imgui"));
-            #[cfg(not(feature = "docking"))]
-            build.include(manifest_dir.join("third-party/imgui-master/imgui"));
+            if docking_enabled {
+                build.include(manifest_dir.join("third-party/imgui-docking/imgui"));
+            } else {
+                build.include(manifest_dir.join("third-party/imgui-master/imgui"));
+            }
         }
 
-        #[cfg(feature = "docking")]
-        let imgui_cpp = "include_imgui_docking.cpp";
-        #[cfg(not(feature = "docking"))]
-        let imgui_cpp = "include_imgui_master.cpp";
+        // Which "all imgui" file to use
+        let imgui_cpp = if docking_enabled {
+             "include_imgui_docking.cpp"
+        } else {
+            "include_imgui_master.cpp"
+        };
 
+        // Set up compiler
         let compiler = build.get_compiler();
 
         // Avoid the if-supported flag functions for easy cases, as they're
@@ -72,6 +70,8 @@ fn main() -> io::Result<()> {
         if compiler.is_like_gnu() || compiler.is_like_clang() {
             build.flag("-fno-exceptions").flag("-fno-rtti");
         }
+
+        // Build imgui lib, suppressing warnings.
         // TODO: disable linking C++ stdlib? Not sure if it's allowed.
         build.warnings(false).file(imgui_cpp).compile("libcimgui.a");
     }