build: Don't tie in tightly with riot-sys

This removes all dependencies on `link=` exported DEP_RIOT_SYS_
variables infavor of parsing riotbuild.h.

build.rs

@@ -3,63 +3,56 @@ extern crate shlex;
 use std::env;
 
 fn main() {
-    let cflags = env::var("DEP_RIOT_SYS_CFLAGS")
-        .expect("DEP_RIOT_SYS_CFLAGS is not set, check whether riot-sys exports it.");
-    let cflags = shlex::split(&cflags).expect("Odd shell escaping in CFLAGS");
-
-    println!("cargo:rerun-if-env-changed=DEP_RIOT_SYS_CFLAGS");
-
-    for flag in cflags.iter() {
-        if flag.starts_with("-DMODULE_") {
-            // Some modules like cmsis-dsp_StatisticsFunctions have funny characters
-            println!(
-                "cargo:rustc-cfg=riot_module_{}",
-                flag[9..].to_lowercase().replace("-", "_")
-            );
+    println!("cargo:rerun-if-env-changed=RIOTBUILD_CONFIG_HEADER_C");
+    let riotbuildh = env::var("RIOTBUILD_CONFIG_HEADER_C")
+        .expect("riotbuild.h is expected to be indicated in the RIOTBUILD_CONFIG_HEADER_C environment variable, or another source of enabled modules provided.");
+    println!("cargo:rerun-if-changed={riotbuildh}");
+
+    let mut defines = std::collections::HashMap::new();
+
+    use std::io::BufRead;
+    for line in std::io::BufReader::new(
+        std::fs::File::open(riotbuildh)
+            .expect("Failed to read riotbuild.h (RIOTBUILD_CONFIG_HEADER_C)"),
+    )
+    .lines()
+    {
+        let line = line.expect("Error reading line from riotbuild.h (RIOTBUILD_CONFIG_HEADER_C)");
+        if let Some(name) = line.strip_prefix("#undef ") {
+            defines.remove(name.trim());
         }
-
-        if flag == "-DDEVELHELP" {
-            println!("cargo:rustc-cfg=riot_develhelp");
+        if let Some((name, val)) = line
+            .strip_prefix("#define ")
+            .and_then(|nv| nv.split_once(" "))
+        {
+            defines.insert(name.trim().to_owned(), val.trim().to_owned());
         }
     }
 
-    let bindgen_output_file = env::var("DEP_RIOT_SYS_BINDGEN_OUTPUT_FILE")
-        .expect("riot-sys did not provide BINDGEN_OUTPUT_FILE");
-
-    let bindgen_output =
-        std::fs::read_to_string(bindgen_output_file).expect("Failed to read BINDGEN_OUTPUT_FILE");
-
     const BOOLEAN_FLAGS: &[&str] = &[
         // This decides whether or not some fields are populated ... and unlike with other
         // structs, the zeroed default is not a good solution here. (It'd kind of work, but
         // it'd produce incorrect debug output).
         "CONFIG_AUTO_INIT_ENABLE_DEBUG",
     ];
 
-    let parsed = syn::parse_file(&bindgen_output).expect("Failed to parse bindgen output");
-    for item in &parsed.items {
-        if let syn::Item::Const(const_) = item {
-            // It's the easiest way to get something we can `contains`...
-            let ident = const_.ident.to_string();
-            if BOOLEAN_FLAGS.contains(&ident.as_str()) {
-                if let syn::Expr::Lit(syn::ExprLit {
-                    lit: syn::Lit::Int(litint),
-                    ..
-                }) = &*const_.expr
-                {
-                    let value: usize = litint
-                        .base10_parse()
-                        .expect("Identifier is integer literal but not parsable");
-                    if value != 0 {
-                        println!("cargo:rustc-cfg=marker_{}", ident.to_lowercase());
-                    }
-                    continue;
-                }
-                panic!(
-                    "Found {} but it's not the literal const it was expected to be",
-                    ident
-                );
-            }
+    for (def, val) in defines {
+        if val != "1" {
+            // So far, only processing boolean flags
+            continue;
+        }
+        if let Some(module) = def.strip_prefix("MODULE_") {
+            // Some modules like cmsis-dsp_StatisticsFunctions have funny characters
+            println!(
+                "cargo:rustc-cfg=riot_module_{}",
+                module.to_lowercase().replace("-", "_")
+            );
+        }
+        if def == "DEVELHELP" {
+            println!("cargo:rustc-cfg=riot_develhelp");
+        }
+        if BOOLEAN_FLAGS.contains(&def.as_str()) {
+            println!("cargo:rustc-cfg=marker_{}", def.to_lowercase());
         }
     }
 }