fix(ninja): compile shared libraries with PIC

CHANGELOG.md

@@ -22,6 +22,10 @@
   `cjson` (v1.7.18), `nanopb` (v0.4.9.1), `lvgl` (v9.2.2), `tinyusb` (v0.18.0), and `unity` (v2.6.1).
 
 ### Fixed
+- **Ninja shared-library sources compile as position-independent code.**
+  Shared-library targets now default to `-fPIC`, while preserving an explicit
+  PIC policy supplied by the target or toolchain
+  (`ebuild/build/ninja_backend.py`).
 - **`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`

ebuild/build/ninja_backend.py

@@ -24,10 +24,11 @@ class PackagePaths:
     libraries: List[str] = field(default_factory=list)
 
 
-# Flags that already request position-independent code. If one of these is
-# present (or explicitly disabled with -fno-*) we must not add -fPIC again.
-_PIC_FLAGS = {"-fPIC", "-fpic", "-fPIE", "-fpie", "-fno-pic", "-fno-PIC",
-              "-fno-pie", "-fno-PIE"}
+# Flags that explicitly control PIC generation. PIE is intentionally excluded:
+# its output is suitable for executables, not shared libraries.
+_PIC_FLAGS = {"-fPIC", "-fpic", "-fno-pic", "-fno-PIC"}
+_PIE_FLAGS = {"-fPIE", "-fpie", "-fno-pie", "-fno-PIE"}
+_POSITION_INDEPENDENCE_FLAGS = _PIC_FLAGS | _PIE_FLAGS
 
 
 def _exe_suffix() -> str:
@@ -146,7 +147,9 @@ def _resolve_target_cflags(self, target) -> List[str]:
         """Resolve all cflags for a target (toolchain + target + packages).
 
         Combines toolchain flags, target-specific flags, include paths,
-        defines, and package include directories into a single list.
+        defines, and package include directories into a single list. Shared
+        library sources default to position-independent code unless the target
+        or toolchain explicitly selects a PIC policy.
 
         Args:
             target: A TargetConfig with cflags, includes, defines, and uses.
@@ -166,6 +169,15 @@ def _resolve_target_cflags(self, target) -> List[str]:
                 for inc_dir in pkg.include_dirs:
                     cflags.append(f"-I{inc_dir}")
 
+        if target.target_type == "shared_library":
+            effective_flag = None
+            for flag in reversed(cflags):
+                if flag in _POSITION_INDEPENDENCE_FLAGS:
+                    effective_flag = flag
+                    break
+            if effective_flag not in _PIC_FLAGS:
+                cflags.append("-fPIC")
+
         return cflags
 
     def _object_path(self, target, src: str) -> Path:

tests/ebuild/test_ninja_backend.py

@@ -62,6 +62,70 @@ def test_shared_library_links_with_the_platform_shared_flag(tmp_path):
     assert ": link_shared " in ninja_file
 
 
+def test_shared_library_sources_default_to_fpic(tmp_path):
+    config = _shared_library_config(tmp_path)
+    toolchain = SimpleNamespace(cc="cc", cxx="c++", ar="ar")
+
+    NinjaBackend(config, tmp_path / "build", toolchain).generate()
+
+    ninja_file = (tmp_path / "build" / "build.ninja").read_text(encoding="utf-8")
+    compile_commands = json.loads(
+        (tmp_path / "build" / "compile_commands.json").read_text(encoding="utf-8")
+    )
+
+    assert "-fPIC" in ninja_file
+    assert "-fPIC" in compile_commands[0]["command"].split()
+
+
+def test_shared_library_respects_explicit_pic_policy(tmp_path):
+    config = _shared_library_config(tmp_path, target_cflags=["-fno-pic"])
+    toolchain = SimpleNamespace(cc="cc", cxx="c++", ar="ar")
+
+    NinjaBackend(config, tmp_path / "build", toolchain).generate()
+
+    compile_commands = json.loads(
+        (tmp_path / "build" / "compile_commands.json").read_text(encoding="utf-8")
+    )
+    flags = compile_commands[0]["command"].split()
+
+    assert "-fno-pic" in flags
+    assert "-fPIC" not in flags
+
+
+@pytest.mark.parametrize("pie_flag", ["-fPIE", "-fpie", "-fno-PIE", "-fno-pie"])
+def test_shared_library_does_not_treat_pie_as_pic(tmp_path, pie_flag):
+    config = _shared_library_config(tmp_path)
+    toolchain = SimpleNamespace(cc="cc", cxx="c++", ar="ar", cflags=[pie_flag])
+
+    NinjaBackend(config, tmp_path / "build", toolchain).generate()
+
+    compile_commands = json.loads(
+        (tmp_path / "build" / "compile_commands.json").read_text(encoding="utf-8")
+    )
+    flags = compile_commands[0]["command"].split()
+
+    assert pie_flag in flags
+    assert "-fPIC" in flags
+
+
+@pytest.mark.parametrize("pie_flag", ["-fPIE", "-fpie", "-fno-PIE", "-fno-pie"])
+def test_shared_library_respects_the_last_position_independence_flag(
+    tmp_path, pie_flag
+):
+    config = _shared_library_config(tmp_path, target_cflags=[pie_flag])
+    toolchain = SimpleNamespace(cc="cc", cxx="c++", ar="ar", cflags=["-fPIC"])
+
+    NinjaBackend(config, tmp_path / "build", toolchain).generate()
+
+    compile_commands = json.loads(
+        (tmp_path / "build" / "compile_commands.json").read_text(encoding="utf-8")
+    )
+    flags = compile_commands[0]["command"].split()
+    pic_and_pie_flags = [flag for flag in flags if flag in {"-fPIC", pie_flag}]
+
+    assert pic_and_pie_flags == ["-fPIC", pie_flag, "-fPIC"]
+
+
 def test_cc_rule_emits_and_consumes_a_depfile(tmp_path):
     """The compile rule must generate a depfile and tell Ninja to read it.