fix(ebuild): preserve toolchain linker flags for shared libraries

CHANGELOG.md

@@ -22,6 +22,9 @@
   `cjson` (v1.7.18), `nanopb` (v0.4.9.1), `lvgl` (v9.2.2), `tinyusb` (v0.18.0), and `unity` (v2.6.1).
 
 ### Fixed
+- Shared-library Ninja link commands now preserve toolchain `extra_ldflags`
+  and `sysroot`, before target linker flags and package library paths, matching
+  executable targets. Previously those toolchain settings were silently ignored.
 - **`ebuild test` now finds Windows test binaries.** The Ninja edge for a
   native `type: test` target already carried the platform suffix
   (`_exe_suffix()` names it `<name>.exe` on Windows), but `ebuild test`

TASKS.md

@@ -11,6 +11,7 @@ Status is one of: `todo`, `in-progress`, `blocked`, `review`, `done`.
 
 | ID | Task | Owner | Mode | Status | Depends on |
 |----|------|-------|------|--------|------------|
+| T-006 | Preserve toolchain linker settings for shared libraries ([#125](https://github.com/embeddedos-org/ebuild/pull/125)) | backend | Verification | review | none |
 | T-002 | Fix Windows Ninja test-target path parsing | backend | Maintenance | review | none |
 | T-003 | `ebuild package` looks for the unsuffixed binary on Windows (`_build/app` rather than `_build/app.exe`) | backend | Maintenance | review | none |
 | T-004 | `_report_footprint` (the flash/RAM report `ebuild build` prints) looks for the unsuffixed binary on Windows, and fails silently rather than logging why | backend | Maintenance | review | none |

ebuild/build/ninja_backend.py

@@ -280,7 +280,7 @@ def _write_ninja(self) -> None:
                     # get, which the rule preamble alone does not supply. The
                     # "build a shared object" flag itself lives in the
                     # link_shared rule, so it must not be repeated here.
-                    ldflags = list(target.ldflags)
+                    ldflags = toolchain_ldflags + list(target.ldflags)
                     libs = []
                     for pkg_name in target.uses:
                         pkg = self.package_paths.get(pkg_name)

tests/unit/test_shared_library_toolchain.py

@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: MIT
+# Copyright (c) 2026 EoS Project
+
+"""Regression tests for toolchain settings in shared-library link commands."""
+
+import shutil
+import sys
+from pathlib import Path
+
+import pytest
+from click.testing import CliRunner
+
+from ebuild.build.ninja_backend import NinjaBackend, PackagePaths
+from ebuild.build.toolchain import ResolvedToolchain
+from ebuild.cli.commands import cli
+from ebuild.core.config import ProjectConfig, TargetConfig
+
+
+@pytest.mark.parametrize("sysroot", [None, "/opt/target-sysroot"])
+def test_shared_link_preserves_toolchain_flags_without_mutation(tmp_path, sysroot):
+    toolchain = ResolvedToolchain(ldflags=["-Wl,--no-undefined"], sysroot=sysroot)
+    targets = [
+        TargetConfig(
+            name=name,
+            target_type="shared_library",
+            sources=[f"{name}.c"],
+            ldflags=[f"-Wl,-soname,lib{name}.so"],
+            uses=[name],
+        )
+        for name in ("first", "second")
+    ]
+    packages = {
+        name: PackagePaths(lib_dirs=[Path(f"vendor/{name}")], libraries=[name])
+        for name in ("first", "second")
+    }
+    config = ProjectConfig(name="libs", version="1.0", targets=targets)
+    NinjaBackend(config, tmp_path, toolchain, packages).generate()
+    manifest = (tmp_path / "build.ninja").read_text(encoding="utf-8")
+
+    for target in targets:
+        edge = next(
+            block for block in manifest.split("\n\n")
+            if ": link_shared " in block and f"lib{target.name}." in block
+        )
+        expected = ["-Wl,--no-undefined"]
+        if sysroot:
+            expected.append(f"--sysroot={sysroot}")
+        expected += target.ldflags + [f"-L{Path('vendor') / target.name}"]
+        assert edge.splitlines()[1:] == [
+            f"  ldflags = {' '.join(expected)}",
+            f"  libs = -l{target.name}",
+        ]
+        assert target.ldflags == [f"-Wl,-soname,lib{target.name}.so"]
+    assert toolchain.ldflags == ["-Wl,--no-undefined"]
+
+
+@pytest.mark.skipif(
+    not sys.platform.startswith("linux") or shutil.which("gcc") is None,
+    reason="requires Linux and GCC for --no-undefined shared-library linking",
+)
+def test_cli_shared_library_honors_toolchain_no_undefined(tmp_path, monkeypatch):
+    pytest.importorskip("ninja", reason="ninja Python package not installed")
+    monkeypatch.chdir(tmp_path)
+    (tmp_path / "build.yaml").write_text(
+        "project:\n  name: shared-link-check\n  version: '1.0'\n"
+        "toolchain:\n  compiler: gcc\n"
+        "  extra_ldflags: ['-Wl,--no-undefined']\n"
+        "targets:\n  - name: example\n    type: shared_library\n"
+        "    sources: [example.c]\n    cflags: [-fPIC]\n",
+        encoding="utf-8",
+    )
+    source = tmp_path / "example.c"
+    source.write_text("int example(void) { return 42; }\n", encoding="utf-8")
+    runner = CliRunner()
+    good = runner.invoke(cli, ["build", "--backend", "ninja", "--build-dir", "good"])
+    assert good.exit_code == 0, good.output
+    assert (tmp_path / "good" / "libexample.so").is_file()
+
+    source.write_text(
+        "extern int missing_symbol(void);\n"
+        "int example(void) { return missing_symbol(); }\n",
+        encoding="utf-8",
+    )
+    # A separate output directory avoids timestamp-based incremental decisions.
+    bad = runner.invoke(cli, ["build", "--backend", "ninja", "--build-dir", "bad"])
+    assert bad.exit_code != 0, bad.output
+    assert "undefined reference" in bad.output, bad.output
+    assert "missing_symbol" in bad.output, bad.output