Remove prints when toolchain is skipped (#1535)

If you have rules_swift in your dependency tree, but don't use swift
anywhere in your build, this still warns is too noisy. Likely the most
common case for this is because grpc depends on rules_apple.

Author: keith

swift/internal/swift_autoconfiguration.bzl

@@ -200,21 +200,14 @@ def _normalized_linux_cpu(cpu):
         return "x86_64"
     return cpu
 
-def _create_linux_toolchain(*, repository_ctx, warn_on_no_swiftc):
+def _create_linux_toolchain(*, repository_ctx):
     """Creates BUILD targets for the Swift toolchain on Linux.
 
     Args:
       repository_ctx: The repository rule context.
-      warn_on_no_swiftc: If True, print a warning if 'swiftc' is not found in
-        $PATH.
     """
     path_to_swiftc = repository_ctx.which("swiftc")
     if not path_to_swiftc:
-        if warn_on_no_swiftc:
-            print("""\
-No 'swiftc' executable found in $PATH. Not auto-generating a Linux Swift \
-toolchain.
-""")  # buildifier: disable=print
         return """\
 # No 'swiftc' executable found in $PATH. Not auto-generating a Linux Swift \
 toolchain.
@@ -314,21 +307,14 @@ def _get_python_bin(repository_ctx):
         return out
     return None
 
-def _create_windows_toolchain(*, repository_ctx, warn_on_no_swiftc):
+def _create_windows_toolchain(*, repository_ctx):
     """Creates BUILD targets for the Swift toolchain on Linux.
 
     Args:
       repository_ctx: The repository rule context.
-      warn_on_no_swiftc: If True, print a warning if 'swiftc.exe' is not found
-        in $PATH.
     """
     path_to_swiftc = repository_ctx.which("swiftc.exe")
     if not path_to_swiftc:
-        if warn_on_no_swiftc:
-            print("""\
-No 'swiftc.exe' executable found in $PATH. Not auto-generating a Windows Swift \
-toolchain.
-""")  # buildifier: disable=print
         return """\
 # No 'swiftc.exe' executable found in $PATH. Not auto-generating a Windows \
 Swift toolchain.
@@ -394,16 +380,6 @@ toolchain(
     )
 
 def _swift_autoconfiguration_impl(repository_ctx):
-    os_name = repository_ctx.os.name.lower()
-    is_linux = False
-    is_windows = False
-    if os_name.startswith("mac os"):
-        pass
-    elif os_name.startswith("windows"):
-        is_windows = True
-    else:
-        is_linux = True
-
     repository_ctx.file(
         "BUILD",
         "\n".join([
@@ -424,14 +400,8 @@ load(
 package(default_visibility = ["//visibility:public"])
 """,
             _create_xcode_toolchain(),
-            _create_windows_toolchain(
-                repository_ctx = repository_ctx,
-                warn_on_no_swiftc = is_windows,
-            ),
-            _create_linux_toolchain(
-                repository_ctx = repository_ctx,
-                warn_on_no_swiftc = is_linux,
-            ),
+            _create_windows_toolchain(repository_ctx = repository_ctx),
+            _create_linux_toolchain(repository_ctx = repository_ctx),
         ]),
     )