[mypyc] Use tabs instead of spaces in emitted C code (#14016)

By using tabs instead of spaces for indentation in the emitted C code we
are able to reduce the file size by almost 9%:

| File | Size |
|------|------|
| `build/__native_74cdc94b2b24dafac2a2.c` (spaces) | 86.5MB |
| `build/__native_74cdc94b2b24dafac2a2.c` (tabs)   | 79.6MB |

For this particular file we save about 6.9MB, or 8.7%.

I checked, and this has no effect on the compilation speed, which is to
be expected. At the very least opening these auto generated files inside
an editor will be faster, even if the compilation isn't any faster.

I am interested in making mypy/mypyc faster, and this seemed like a
low-hanging fruit that could be beneficial.

mypyc/codegen/emit.py

@@ -176,10 +176,10 @@ def __init__(
     # Low-level operations
 
     def indent(self) -> None:
-        self._indent += 4
+        self._indent += 1
 
     def dedent(self) -> None:
-        self._indent -= 4
+        self._indent -= 1
         assert self._indent >= 0
 
     def label(self, label: BasicBlock) -> str:
@@ -194,7 +194,7 @@ def attr(self, name: str) -> str:
     def emit_line(self, line: str = "") -> None:
         if line.startswith("}"):
             self.dedent()
-        self.fragments.append(self._indent * " " + line + "\n")
+        self.fragments.append(self._indent * "\t" + line + "\n")
         if line.endswith("{"):
             self.indent()
 

mypyc/test/test_emit.py

@@ -28,4 +28,4 @@ def test_emit_line(self) -> None:
         emitter.emit_line("a {")
         emitter.emit_line("f();")
         emitter.emit_line("}")
-        assert emitter.fragments == ["line;\n", "a {\n", "    f();\n", "}\n"]
+        assert emitter.fragments == ["line;\n", "a {\n", "\tf();\n", "}\n"]

mypyc/test/test_emitfunc.py

@@ -833,7 +833,7 @@ def assert_emit(
 
         op.accept(visitor)
         frags = declarations.fragments + emitter.fragments
-        actual_lines = [line.strip(" ") for line in frags]
+        actual_lines = [line.strip(" \t") for line in frags]
         assert all(line.endswith("\n") for line in actual_lines)
         actual_lines = [line.rstrip("\n") for line in actual_lines]
         if not expected.strip():
@@ -900,7 +900,7 @@ def test_simple(self) -> None:
                 "    return cpy_r_arg;\n",
                 "}\n",
             ],
-            result,
+            [line.replace("\t", 4 * " ") for line in result],
             msg="Generated code invalid",
         )
 
@@ -927,6 +927,6 @@ def test_register(self) -> None:
                 "    CPy_Unreachable();\n",
                 "}\n",
             ],
-            result,
+            [line.replace("\t", 4 * " ") for line in result],
             msg="Generated code invalid",
         )

mypyc/test/test_emitwrapper.py

@@ -56,5 +56,6 @@ def test_check_int(self) -> None:
         )
 
     def assert_lines(self, expected: list[str], actual: list[str]) -> None:
-        actual = [line.rstrip("\n") for line in actual]
+        actual = [line.rstrip("\n").replace(4 * " ", "\t") for line in actual]
+        expected = [line.replace(4 * " ", "\t") for line in expected]
         assert_string_arrays_equal(expected, actual, "Invalid output")