[DOCs][Added] Notes about using booleans in definitions

Also a warning for complex data types

See #762

docs/source/configuration/substitution.rst

@@ -58,6 +58,10 @@ Note that from the YAML point this is two documents in the same file.
 The second document is used to provide default values for the
 definitions. As defaults they have the lowest precedence.
 
+.. warning::
+   Be careful about using booleans in definitions. Note that `on`, `off`, `yes`, `no`, etc. are
+   usually interpreted as booleans in YAML. Use quotes in the definition and/or in the place
+   where the value is expanded to avoid ambiguity.
 
 .. index::
    pair: definitions; during import

kibot/config_reader.py

@@ -24,7 +24,7 @@
 from .error import KiPlotConfigurationError, config_error
 from .misc import (NO_YAML_MODULE, EXIT_BAD_ARGS, EXAMPLE_CFG, WONT_OVERWRITE, W_NOOUTPUTS, W_UNKOUT, W_NOFILTERS,
                    W_NOVARIANTS, W_NOGLOBALS, TRY_INSTALL_CHECK, W_NOPREFLIGHTS, W_NOGROUPS, W_NEWGROUP, error_level_to_name,
-                   DEFAULT_ROTATIONS, DEFAULT_OFFSETS, W_EXTRADOCS, RE_LEN)
+                   DEFAULT_ROTATIONS, DEFAULT_OFFSETS, W_EXTRADOCS, RE_LEN, W_DEFNOSTR)
 from .gs import GS
 from .registrable import RegOutput, RegVariant, RegFilter, RegDependency
 from .pre_base import BasePreFlight
@@ -80,7 +80,14 @@ def do_replace(k, v, content, replaced):
         # Handle empty definitions keeping YAML's "null"
         if v is None:
             v = 'null'
-        logger.debugl(2, '- Replacing {} -> {}'.format(key, v))
+        if isinstance(v, bool):
+            v = str(v).lower()  # True/False is also valid
+        if isinstance(v, (int, float)):
+            v = str(v)
+        if not isinstance(v, str):
+            logger.warning(W_DEFNOSTR+f'Please only use simple data types for definitions (`{k}` contains `{v}`'
+                           f' which is `{type(v).__name__}` type)')
+        logger.debugl(2, f'- Replacing {key} -> {v} ({type(v)})')
         content = content.replace(key, str(v))
         replaced = True
     return content, replaced

kibot/misc.py

@@ -332,6 +332,7 @@
 W_NOBOMOPS = '(W169) '
 W_NODRILL = '(W170) '
 W_NOPCBTB = '(W171) '
+W_DEFNOSTR = '(W172) '
 # Somehow arbitrary, the colors are real, but can be different
 PCB_MAT_COLORS = {'fr1': "937042", 'fr2': "949d70", 'fr3': "adacb4", 'fr4': "332B16", 'fr5': "6cc290"}
 PCB_FINISH_COLORS = {'hal': "8b898c", 'hasl': "8b898c", 'imag': "8b898c", 'enig': "cfb96e", 'enepig': "cfb96e",