[core] Fix the native ESP8266 and host builds on Windows without ccache (#20468)

tests/unit_tests/build_gen/test_arduino8266.py

@@ -888,8 +888,9 @@ def test_write_project_plain_asm_rule_skips_preprocessor(tmp_path: Path) -> None
     _set_flags()
     content = _write_ninja(paths)
     assert "lowlevel.s.o: asm " in content
+    assert "rule asm\n  command = $cc -x assembler $asflags -c $in -o $out" in content
     assert "rule asm\n  command = $ccache $cc -x assembler $asflags -c $in -o $out" in (
-        content
+        _write_ninja(paths, ccache="/cc/ccache")
     )
 
 

tests/unit_tests/build_gen/test_host.py

@@ -308,7 +308,10 @@ def test_write_project_pch_skipped_for_a_force_include_in_the_compiler(
 def test_write_project_without_ccache(tmp_path: Path) -> None:
     _make_src(tmp_path, "main.cpp")
     _changed, ninja = _render()
-    assert "ccache = \n" in ninja
+    # No launcher variable, and no leading space on the commands either:
+    # CreateProcess on Windows rejects a command line that starts with one
+    assert "$ccache" not in ninja
+    assert "  command = $cxx -MMD -MF $out.d" in ninja
 
 
 def test_write_project_routes_user_link_flags(tmp_path: Path) -> None:

tests/unit_tests/build_helpers/test_ninja_gen.py

@@ -55,3 +55,21 @@ def test_collect_sources_skips_excluded_and_other_files(tmp_path: Path) -> None:
         tmp_path / "b.cpp",
         tmp_path / "sub" / "c.S",
     ]
+
+
+@pytest.mark.parametrize("ccache", ["/usr/bin/ccache", None])
+def test_compile_rule_lines_splice_the_launcher(ccache: str | None) -> None:
+    """Without ccache no command keeps a leading space, which CreateProcess
+    on Windows rejects; with it every compile rule starts with the launcher."""
+    commands = [
+        line.removeprefix("  command = ")
+        for line in ninja_gen.compile_rule_lines(ccache)
+        if line.startswith("  command = ")
+    ]
+    assert len(commands) == 4
+    for command in commands:
+        if ccache:
+            assert command.startswith("$ccache $c")
+        else:
+            assert command.startswith("$c")
+            assert "$ccache" not in command