Added:

- Toolchain overrides via `[toolchain]` and env (`DCR_*`)
- ASM `.S` preprocessing via GCC/Clang (`-x assembler-with-cpp`)

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## [0.2.7] - 2026-03-03
+Added:
+- Toolchain overrides via `[toolchain]` and env (`DCR_*`)
+- ASM `.S` preprocessing via GCC/Clang (`-x assembler-with-cpp`)
+
 ## [0.2.6] - 2026-03-01
 Added:
 - `sharedlib` build kind (shared library output)

Cargo.lock

@@ -90,7 +90,7 @@ dependencies = [
 
 [[package]]
 name = "dcr"
-version = "0.2.6"
+version = "0.2.7"
 dependencies = [
  "reqwest",
  "self-replace",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dcr"
-version = "0.2.6"
+version = "0.2.7"
 edition = "2024"
 build = "build.rs"
 

README.md

@@ -146,6 +146,14 @@ compiler = "clang"
 cflags = ["-Wall", "-Wextra"]
 ldflags = ["-lm"]
 
+[toolchain]
+# Optional tool overrides:
+# cc = "clang"
+# cxx = "clang++"
+# as = "as"
+# ar = "ar"
+# ld = "ld"
+
 [dependencies]
 ```
 

TODO.md

@@ -3,7 +3,5 @@
 - Add header dependency tracking for incremental builds (GCC/Clang: -MMD, MSVC: /showIncludes)
 - Add external package managers (Conan, vcpkg)
 - Multi-target
-- ASM support
 - Linker script + direct linker control
-- Custom targets/steps
-- Tool overrides and env vars
+- Custom targets/steps

docs/configuration/build-section.md

@@ -26,6 +26,17 @@ kind = "bin"
 - `cflags` (string array, optional): extra compile flags.
 - `ldflags` (string array, optional): extra link flags.
 
+## Toolchain section
+
+```toml
+[toolchain]
+cc = "clang"
+cxx = "clang++"
+as = "as"
+ar = "ar"
+ld = "ld"
+```
+
 ## Behavior notes
 
 - Compiler backend is selected by compiler string (`gcc`, `clang`, `cl`, `clang-cl`).

docs/dependencies-and-build/compilers-and-linking.md

@@ -39,6 +39,18 @@ If `build.platform` is set, DCR passes it as an architecture hint:
 - GCC/Clang: `-march=<platform>`
 - MSVC: maps to `/arch:*` for known values (`x86`, `i386`, `i486`, `i586`, `i686`, `sse2`, `avx`, `avx2`)
 
+## Toolchain overrides
+
+If `[toolchain]` is set, DCR uses its values to override compiler/linker tools:
+
+- `cc`, `cxx`, `as` override compilers for C/C++/ASM
+- `ar` overrides the archiver (used for `staticlib`)
+- `ld` overrides the linker (used by GCC/Clang/NASM/GAS backends)
+
+Environment overrides (highest priority):
+- `DCR_COMPILER` (all languages)
+- `DCR_CC`, `DCR_CXX`, `DCR_AS`, `DCR_AR`, `DCR_LD`
+
 ## Linking
 
 For `kind = "bin"`:

docs/reference-and-help/config-reference.md

@@ -17,6 +17,13 @@ platform = "string"            # optional
 cflags = ["string", "..."]     # optional
 ldflags = ["string", "..."]    # optional
 
+[toolchain]
+cc = "string"   # optional
+cxx = "string"  # optional
+as = "string"   # optional
+ar = "string"   # optional
+ld = "string"   # optional
+
 [dependencies]
 name = {
   path = "string",              # required for each dependency

src/cli/build.rs

@@ -33,6 +33,11 @@ pub fn build(args: &[String]) -> i32 {
     let build_target = get_config_str(&config, "build.target");
     let build_kind = get_config_str(&config, "build.kind");
     let build_platform = get_config_str(&config, "build.platform");
+    let tc_cc = get_config_opt(&config, "toolchain.cc");
+    let tc_cxx = get_config_opt(&config, "toolchain.cxx");
+    let tc_as = get_config_opt(&config, "toolchain.as");
+    let tc_ar = get_config_opt(&config, "toolchain.ar");
+    let tc_ld = get_config_opt(&config, "toolchain.ld");
     let build_cflags = match get_config_list(&config, "build.cflags") {
         Ok(v) => v,
         Err(msg) => {
@@ -48,11 +53,21 @@ pub fn build(args: &[String]) -> i32 {
         }
     };
 
+    let resolved_compiler = resolve_compiler(
+        &build_language,
+        &project_compiler,
+        tc_cc.as_deref(),
+        tc_cxx.as_deref(),
+        tc_as.as_deref(),
+    );
+    let resolved_linker = resolve_tool("DCR_LD", tc_ld.as_deref());
+    let resolved_archiver = resolve_tool("DCR_AR", tc_ar.as_deref());
+
     println!(
         "    Building project `{}`\n    Profile: {}\n    Compiler: {}\n",
         colored(&project_name, BOLD_GREEN),
         colored(&active_profile, BOLD_GREEN),
-        colored(&project_compiler, BOLD_GREEN)
+        colored(&resolved_compiler, BOLD_GREEN)
     );
 
     ensure_target_dirs(&items, &active_profile, normalize_target(&build_target));
@@ -74,12 +89,14 @@ pub fn build(args: &[String]) -> i32 {
     let ctx = BuildContext {
         profile: &active_profile,
         project_name: &project_name,
-        compiler: &project_compiler,
+        compiler: &resolved_compiler,
         language: &build_language,
         standard: &build_standard,
         target_dir: normalize_target(&build_target),
         kind: normalize_kind(&build_kind),
         platform: normalize_platform(&build_platform),
+        linker: resolved_linker.as_deref(),
+        archiver: resolved_archiver.as_deref(),
         include_dirs: &resolved.include_dirs,
         lib_dirs: &resolved.lib_dirs,
         libs: &resolved.libs,
@@ -126,6 +143,16 @@ fn get_config_str(config: &Config, key: &str) -> String {
         .to_string()
 }
 
+fn get_config_opt(config: &Config, key: &str) -> Option<String> {
+    let value = config.get(key)?.as_str()?;
+    let trimmed = value.trim();
+    if trimmed.is_empty() {
+        None
+    } else {
+        Some(trimmed.to_string())
+    }
+}
+
 fn get_config_list(config: &Config, key: &str) -> Result<Vec<String>, String> {
     let value = match config.get(key) {
         Some(v) => v,
@@ -195,3 +222,76 @@ fn normalize_platform(platform: &str) -> Option<&str> {
         Some(trimmed)
     }
 }
+
+fn resolve_compiler(
+    language: &str,
+    compiler: &str,
+    tc_cc: Option<&str>,
+    tc_cxx: Option<&str>,
+    tc_as: Option<&str>,
+) -> String {
+    let lang = language.to_lowercase();
+    env_override_compiler(&lang)
+        .or_else(|| toolchain_override_compiler(&lang, tc_cc, tc_cxx, tc_as))
+        .unwrap_or_else(|| compiler.to_string())
+}
+
+fn env_override_compiler(lang: &str) -> Option<String> {
+    if let Ok(value) = std::env::var("DCR_COMPILER") {
+        let trimmed = value.trim();
+        if !trimmed.is_empty() {
+            return Some(trimmed.to_string());
+        }
+    }
+    if lang == "asm" {
+        if let Ok(value) = std::env::var("DCR_AS") {
+            let trimmed = value.trim();
+            if !trimmed.is_empty() {
+                return Some(trimmed.to_string());
+            }
+        }
+        return None;
+    }
+    if (lang == "c++" || lang == "cpp" || lang == "cxx")
+        && let Ok(value) = std::env::var("DCR_CXX")
+    {
+        let trimmed = value.trim();
+        if !trimmed.is_empty() {
+            return Some(trimmed.to_string());
+        }
+    }
+    if let Ok(value) = std::env::var("DCR_CC") {
+        let trimmed = value.trim();
+        if !trimmed.is_empty() {
+            return Some(trimmed.to_string());
+        }
+    }
+    None
+}
+
+fn toolchain_override_compiler(
+    lang: &str,
+    tc_cc: Option<&str>,
+    tc_cxx: Option<&str>,
+    tc_as: Option<&str>,
+) -> Option<String> {
+    if lang == "asm" {
+        return tc_as.map(|v| v.to_string());
+    }
+    if (lang == "c++" || lang == "cpp" || lang == "cxx")
+        && let Some(v) = tc_cxx
+    {
+        return Some(v.to_string());
+    }
+    tc_cc.map(|v| v.to_string())
+}
+
+fn resolve_tool(env_key: &str, fallback: Option<&str>) -> Option<String> {
+    if let Ok(value) = std::env::var(env_key) {
+        let trimmed = value.trim();
+        if !trimmed.is_empty() {
+            return Some(trimmed.to_string());
+        }
+    }
+    fallback.map(|v| v.to_string())
+}

src/core/builder/clang.rs

@@ -18,7 +18,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     if ctx.kind == "staticlib" {
         let lib_path = platform::lib_path(ctx.profile, ctx.project_name, ctx.target_dir);
-        let mut cmd = Command::new("ar");
+        let mut cmd = Command::new(ctx.archiver.unwrap_or("ar"));
         cmd.arg("rcs").arg(&lib_path);
         for obj in &objects {
             cmd.arg(obj);
@@ -33,7 +33,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         }
     }
 
-    let mut cmd = Command::new(compiler);
+    let mut cmd = Command::new(ctx.linker.unwrap_or(compiler));
     if ctx.kind == "sharedlib" {
         if cfg!(target_os = "macos") {
             cmd.arg("-dynamiclib");
@@ -150,6 +150,9 @@ fn build_objects(
             if ctx.kind == "sharedlib" {
                 cmd.arg("-fPIC");
             }
+            if let Some(flag) = asm_lang_flag(source) {
+                cmd.arg("-x").arg(flag);
+            }
             if let Some(platform) = ctx.platform
                 && !platform.trim().is_empty()
             {
@@ -178,6 +181,15 @@ fn build_objects(
     Ok(objects)
 }
 
+fn asm_lang_flag(source: &str) -> Option<&'static str> {
+    let ext = Path::new(source).extension().and_then(|v| v.to_str())?;
+    match ext {
+        "S" => Some("assembler-with-cpp"),
+        "s" | "asm" => Some("assembler"),
+        _ => None,
+    }
+}
+
 fn object_path(obj_dir: &Path, source: &str, obj_ext: &str) -> String {
     let src_path = Path::new(source);
     let rel = src_path

src/core/builder/gas.rs

@@ -21,12 +21,13 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     if ctx.kind == "staticlib" {
         let lib_path = platform::lib_path(ctx.profile, ctx.project_name, ctx.target_dir);
-        let mut cmd = Command::new(if cfg!(target_os = "windows") {
+        let archiver = ctx.archiver.unwrap_or(if cfg!(target_os = "windows") {
             "lib"
         } else {
             "ar"
         });
-        if cfg!(target_os = "windows") {
+        let mut cmd = Command::new(archiver);
+        if cfg!(target_os = "windows") && archiver == "lib" {
             cmd.arg("/nologo").arg(format!("/OUT:{lib_path}"));
         } else {
             cmd.arg("rcs").arg(&lib_path);
@@ -44,7 +45,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         }
     }
 
-    let mut cmd = Command::new("cc");
+    let mut cmd = Command::new(ctx.linker.unwrap_or("cc"));
     if ctx.kind == "sharedlib" {
         if cfg!(target_os = "macos") {
             cmd.arg("-dynamiclib");

src/core/builder/gcc.rs

@@ -18,7 +18,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     if ctx.kind == "staticlib" {
         let lib_path = platform::lib_path(ctx.profile, ctx.project_name, ctx.target_dir);
-        let mut cmd = Command::new("ar");
+        let mut cmd = Command::new(ctx.archiver.unwrap_or("ar"));
         cmd.arg("rcs").arg(&lib_path);
         for obj in &objects {
             cmd.arg(obj);
@@ -33,7 +33,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         }
     }
 
-    let mut cmd = Command::new(compiler);
+    let mut cmd = Command::new(ctx.linker.unwrap_or(compiler));
     if ctx.kind == "sharedlib" {
         if cfg!(target_os = "macos") {
             cmd.arg("-dynamiclib");
@@ -150,6 +150,9 @@ fn build_objects(
             if ctx.kind == "sharedlib" {
                 cmd.arg("-fPIC");
             }
+            if let Some(flag) = asm_lang_flag(source) {
+                cmd.arg("-x").arg(flag);
+            }
             if let Some(platform) = ctx.platform
                 && !platform.trim().is_empty()
             {
@@ -178,6 +181,15 @@ fn build_objects(
     Ok(objects)
 }
 
+fn asm_lang_flag(source: &str) -> Option<&'static str> {
+    let ext = Path::new(source).extension().and_then(|v| v.to_str())?;
+    match ext {
+        "S" => Some("assembler-with-cpp"),
+        "s" | "asm" => Some("assembler"),
+        _ => None,
+    }
+}
+
 fn object_path(obj_dir: &Path, source: &str, obj_ext: &str) -> String {
     let src_path = Path::new(source);
     let rel = src_path

src/core/builder/mod.rs

@@ -13,6 +13,8 @@ pub struct BuildContext<'a> {
     pub target_dir: Option<&'a str>,
     pub kind: &'a str,
     pub platform: Option<&'a str>,
+    pub linker: Option<&'a str>,
+    pub archiver: Option<&'a str>,
     pub include_dirs: &'a [String],
     pub lib_dirs: &'a [String],
     pub libs: &'a [String],

src/core/builder/msvc.rs

@@ -21,7 +21,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     if ctx.kind == "staticlib" {
         let lib_path = platform::lib_path(ctx.profile, ctx.project_name, ctx.target_dir);
-        let mut cmd = Command::new("lib");
+        let mut cmd = Command::new(ctx.archiver.unwrap_or("lib"));
         cmd.arg("/nologo").arg(format!("/OUT:{lib_path}"));
         for obj in &objects {
             cmd.arg(obj);

src/core/builder/nasm.rs

@@ -21,12 +21,13 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
 
     if ctx.kind == "staticlib" {
         let lib_path = platform::lib_path(ctx.profile, ctx.project_name, ctx.target_dir);
-        let mut cmd = Command::new(if cfg!(target_os = "windows") {
+        let archiver = ctx.archiver.unwrap_or(if cfg!(target_os = "windows") {
             "lib"
         } else {
             "ar"
         });
-        if cfg!(target_os = "windows") {
+        let mut cmd = Command::new(archiver);
+        if cfg!(target_os = "windows") && archiver == "lib" {
             cmd.arg("/nologo").arg(format!("/OUT:{lib_path}"));
         } else {
             cmd.arg("rcs").arg(&lib_path);
@@ -44,8 +45,7 @@ pub fn build(ctx: &BuildContext) -> Result<f64, String> {
         }
     }
 
-    let linker = "cc";
-    let mut cmd = Command::new(linker);
+    let mut cmd = Command::new(ctx.linker.unwrap_or("cc"));
     if ctx.kind == "sharedlib" {
         if cfg!(target_os = "macos") {
             cmd.arg("-dynamiclib");

src/core/config.rs

@@ -129,6 +129,15 @@ impl Config {
         {
             return Err(ConfigError::Invalid("build.platform is empty".into()));
         }
+        if let Some(toolchain) = self.get("toolchain").and_then(|v| v.as_table()) {
+            for key in ["cc", "cxx", "as", "ar", "ld"] {
+                if let Some(v) = toolchain.get(key)
+                    && !v.as_str().map(|s| !s.trim().is_empty()).unwrap_or(false)
+                {
+                    return Err(ConfigError::Invalid(format!("toolchain.{key} is invalid")));
+                }
+            }
+        }
         if let Some(kind) = build.get("kind").and_then(|v| v.as_str()) {
             let kind = kind.trim();
             if kind != "bin" && kind != "staticlib" && kind != "sharedlib" {
@@ -213,6 +222,7 @@ fn format_toml(value: &Value) -> Result<String, ConfigError> {
         .get("dependencies")
         .and_then(|v| v.as_table())
         .ok_or_else(|| ConfigError::Invalid("missing [dependencies]".into()))?;
+    let toolchain = root.get("toolchain").and_then(|v| v.as_table());
 
     let name = package.get("name").and_then(|v| v.as_str()).unwrap_or("");
     let version = package
@@ -251,6 +261,24 @@ fn format_toml(value: &Value) -> Result<String, ConfigError> {
     }
     out.push('\n');
 
+    if let Some(toolchain) = toolchain {
+        let mut lines = Vec::new();
+        for key in ["cc", "cxx", "as", "ar", "ld"] {
+            if let Some(value) = toolchain.get(key).and_then(|v| v.as_str())
+                && !value.trim().is_empty()
+            {
+                lines.push(format!("{key} = \"{value}\""));
+            }
+        }
+        if !lines.is_empty() {
+            out.push_str("[toolchain]\n");
+            for line in lines {
+                out.push_str(&format!("{line}\n"));
+            }
+            out.push('\n');
+        }
+    }
+
     out.push_str("[dependencies]\n");
     if !deps.is_empty() {
         let mut keys: Vec<&String> = deps.keys().collect();