explain the logic a bit

Author: tshepang

config.toml.example

@@ -313,10 +313,12 @@
 
 # Whether or not debug assertions are enabled for the compiler and standard
 # library.
+# Defaults to rust.debug value.
 #debug-assertions = false
 
 # Whether or not debug assertions are enabled for the standard library.
 # Overrides the `debug-assertions` option, if defined.
+# Defaults to rust.debug value.
 #debug-assertions-std = false
 
 # Debuginfo level for most of Rust code, corresponds to the `-C debuginfo=N` option of `rustc`.
@@ -326,16 +328,21 @@
 # Can be overridden for specific subsets of Rust code (rustc, std or tools).
 # Debuginfo for tests run with compiletest is not controlled by this option
 # and needs to be enabled separately with `debuginfo-level-tests`.
-#debuginfo-level = if debug { 2 } else { 0 }
+#
+# If debug is true, this defaults to 2.
+#debuginfo-level = 0
 
 # Debuginfo level for the compiler.
-#debuginfo-level-rustc = debuginfo-level
+# Defaults to rust.debuginfo-level value.
+#debuginfo-level-rustc = 0
 
 # Debuginfo level for the standard library.
-#debuginfo-level-std = debuginfo-level
+# Defaults to rust.debuginfo-level value.
+#debuginfo-level-std = 0
 
 # Debuginfo level for the tools.
-#debuginfo-level-tools = debuginfo-level
+# Defaults to rust.debuginfo-level value.
+#debuginfo-level-tools = 0
 
 # Debuginfo level for the test suites run with compiletest.
 # FIXME(#61117): Some tests fail when this option is enabled.