Replace small C lib with std C lib if not supported for a given target

Author: hugueskamba

tools/build.py

@@ -39,6 +39,7 @@
 from tools.build_api import print_build_results
 from tools.build_api import target_supports_toolchain
 from tools.build_api import find_valid_toolchain
+from tools.build_api import check_small_c_lib_support
 from tools.notifier.term import TerminalNotifier
 from tools.utils import argparse_filestring_type, args_error, argparse_many
 from tools.utils import argparse_dir_not_parent
@@ -177,6 +178,10 @@ def main():
             except NoValidToolchainException as e:
                 print_end_warnings(e.end_warnings)
                 args_error(parser, str(e))
+
+            warning = check_small_c_lib_swap(target, toolchain_name)
+            end_warnings += [warning] if warning is not None else []
+
             tt_id = "%s::%s" % (internal_tc_name, target_name)
             if not target_supports_toolchain(target, toolchain_name):
                 # Log this later

tools/build_api.py

@@ -52,6 +52,11 @@
 
 RELEASE_VERSIONS = ['2', '5']
 
+SMALL_C_LIB_CHANGE_WARNING = (
+    "Warning: We noticed that you are using target.c_lib set to small. "
+    "As the {} target does not support a small C library for the {} toolchain, we are using the standard C library instead. "
+)
+
 def prep_report(report, target_name, toolchain_name, id_name):
     """Setup report keys
 
@@ -205,6 +210,27 @@ def get_toolchain_name(target, toolchain_name):
 
     return toolchain_name
 
+
+def check_small_c_lib_support(target, toolchain_name):
+    """
+    Check if the small C lib is supported.
+    If it is not supported and the standard C library is supported, the later will be used instead.
+    Return a warning if the standard C lib will be used instead of the small C lib.
+    """
+    if (
+        hasattr(target, "c_lib")
+        and target.c_lib.lower() == "small"
+        and hasattr(target, "supported_c_libs")
+        and toolchain_name not in target.supported_c_libs
+    ):
+        if (
+            "small" not in target.supported_c_libs[toolchain_name]
+            and "std" in target.supported_c_libs[toolchain_name]
+        ):
+            return SMALL_C_LIB_CHANGE_WARNING.format(target.name, toolchain_name)
+
+
+
 def find_valid_toolchain(target, toolchain):
     """Given a target and toolchain, get the names for the appropriate
     toolchain to use. The environment is also checked to see if the corresponding
@@ -250,6 +276,7 @@ def find_valid_toolchain(target, toolchain):
                 and "uARM" in {toolchain_name, target.default_toolchain}
             ):
                 end_warnings.append(UARM_TOOLCHAIN_WARNING)
+
             return toolchain_name, internal_tc_name, end_warnings
     else:
         if last_error:

tools/toolchains/mbed_toolchain.py

@@ -1111,7 +1111,17 @@ def check_c_lib_supported(self, target, toolchain):
                    "target.default_lib is no longer supported, please use target.c_lib for C library selection."
                 )
         if  hasattr(target, "c_lib"):
+
             target.c_lib = target.c_lib.lower()
+
+            if (
+                target.c_lib == "small"
+                and hasattr(target, "supported_c_libs")
+                and "small" not in target.supported_c_libs[toolchain]
+                and "std" in target.supported_c_libs[toolchain]
+            ):
+                target.c_lib = "std"
+
             if (
                 hasattr(target, "supported_c_libs") == False
                 or toolchain not in target.supported_c_libs