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

esphome/build_gen/arduino8266.py

@@ -1057,7 +1057,7 @@ def write_project(paths: InstalledPaths, ccache: str | None) -> bool:
     cxx = (toolchain_tool(paths.toolchain, "g++"),)
     lines = [
         *tool_lines((toolchain_tool(paths.toolchain, "gcc"),), cxx, ccache),
-        *compile_rule_lines(),
+        *compile_rule_lines(ccache),
         *ar_rule_lines(toolchain_tool(paths.toolchain, "ar")),
         *pch_rule_lines(),
         "rule link",

esphome/build_gen/host.py

@@ -240,7 +240,7 @@ def write_project(compilers: HostCompilers, ccache: str | None) -> bool:
 
     lines = [
         *tool_lines(compilers.cc, compilers.cxx, ccache),
-        *compile_rule_lines(),
+        *compile_rule_lines(ccache),
         *pch_rule_lines(),
         "rule link",
         "  command = $cxx -o $out $linkflags @$out.rsp $archives $libdirflags $libflags",

esphome/build_helpers/ninja_gen.py

@@ -74,33 +74,40 @@ def tool_lines(
         # path gets
         f"python = {_q(strip_win_long_path_prefix(sys.executable))}",
         f"buildtool = {_q(_BUILD_TOOL)}",
-        f"ccache = {_q(ccache) if ccache else ''}",
+        *([f"ccache = {_q(ccache)}"] if ccache else []),
         "",
     ]
 
 
-def compile_rule_lines() -> list[str]:
-    """The compile rules; ``$own_includes`` is empty unless an edge sets it."""
+def compile_rule_lines(ccache: str | None) -> list[str]:
+    """The compile rules; ``$own_includes`` is empty unless an edge sets it.
+
+    ``ccache`` is the launcher ``tool_lines`` was given; the same test here
+    keeps the variable and the rules in step. It is spliced in rather than
+    left as an empty variable: a leading space on the command line makes
+    CreateProcess fail on Windows.
+    """
+    launcher = "$ccache " if ccache else ""
     return [
         "rule c",
-        "  command = $ccache $cc -MMD -MF $out.d $own_includes $cflags $flags -c $in -o $out",
+        f"  command = {launcher}$cc -MMD -MF $out.d $own_includes $cflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = CC $out",
         "rule cxx",
-        "  command = $ccache $cxx -MMD -MF $out.d $own_includes $cxxflags $flags -c $in -o $out",
+        f"  command = {launcher}$cxx -MMD -MF $out.d $own_includes $cxxflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = CXX $out",
         "rule aspp",
-        "  command = $ccache $cc -MMD -MF $out.d -x assembler-with-cpp $own_includes $asflags $flags -c $in -o $out",
+        f"  command = {launcher}$cc -MMD -MF $out.d -x assembler-with-cpp $own_includes $asflags $flags -c $in -o $out",
         "  depfile = $out.d",
         "  deps = gcc",
         "  description = AS $out",
         # Plain assembler, as SCons's ASCOM: no preprocessor, so no
         # depfile and no $flags (defines/includes) either
         "rule asm",
-        "  command = $ccache $cc -x assembler $asflags -c $in -o $out",
+        f"  command = {launcher}$cc -x assembler $asflags -c $in -o $out",
         "  description = AS $out",
     ]
 

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