interpreter: add a special class to track the lifecycle of get_option() strings

(cherry picked from commit e19e9ce6f196f7c127a2668b5df0ada1d50806df)

3 files changed, 34 insertions, 2 deletions

diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index 6cd5441e6..50ec79569 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -446,6 +446,7 @@ class Interpreter(InterpreterBase, HoldableObject):
             str: P_OBJ.StringHolder,
             P_OBJ.MesonVersionString: P_OBJ.MesonVersionStringHolder,
             P_OBJ.DependencyVariableString: P_OBJ.DependencyVariableStringHolder,
+            P_OBJ.OptionString: P_OBJ.OptionStringHolder,
 
             # Meson types
             mesonlib.File: OBJ.FileHolder,
@@ -1093,6 +1094,8 @@ class Interpreter(InterpreterBase, HoldableObject):
             opt.name = optname
             return opt
         elif isinstance(opt, coredata.UserOption):
+            if isinstance(opt.value, str):
+                return P_OBJ.OptionString(opt.value, f'{{{optname}}}')
             return opt.value
         return opt
 
@@ -2819,6 +2822,9 @@ class Interpreter(InterpreterBase, HoldableObject):
         ret = os.path.join(*parts).replace('\\', '/')
         if isinstance(parts[0], P_OBJ.DependencyVariableString) and '..' not in other:
             return P_OBJ.DependencyVariableString(ret)
+        elif isinstance(parts[0], P_OBJ.OptionString):
+            name = os.path.join(parts[0].optname, other)
+            return P_OBJ.OptionString(ret, name)
         else:
             return ret
 
diff --git a/mesonbuild/interpreter/primitives/__init__.py b/mesonbuild/interpreter/primitives/__init__.py
index 1874d0d81..5bbd959ea 100644
--- a/mesonbuild/interpreter/primitives/__init__.py
+++ b/mesonbuild/interpreter/primitives/__init__.py
@@ -22,5 +22,6 @@ from .range import RangeHolder
 from .string import (
     StringHolder,
     MesonVersionString, MesonVersionStringHolder,
-    DependencyVariableString, DependencyVariableStringHolder
+    DependencyVariableString, DependencyVariableStringHolder,
+    OptionString, OptionStringHolder,
 )
diff --git a/mesonbuild/interpreter/primitives/string.py b/mesonbuild/interpreter/primitives/string.py
index 9abca7525..0c635a20a 100644
--- a/mesonbuild/interpreter/primitives/string.py
+++ b/mesonbuild/interpreter/primitives/string.py
@@ -157,10 +157,14 @@ class StringHolder(ObjectHolder[str]):
     def version_compare_method(self, args: T.Tuple[str], kwargs: TYPE_kwargs) -> bool:
         return version_compare(self.held_object, args[0])
 
+    @staticmethod
+    def _op_div(this: str, other: str) -> str:
+        return os.path.join(this, other).replace('\\', '/')
+
     @FeatureNew('/ with string arguments', '0.49.0')
     @typed_operator(MesonOperator.DIV, str)
     def op_div(self, other: str) -> str:
-        return os.path.join(self.held_object, other).replace('\\', '/')
+        return self._op_div(self.held_object, other)
 
     @typed_operator(MesonOperator.INDEX, int)
     def op_index(self, other: int) -> str:
@@ -194,3 +198,24 @@ class DependencyVariableStringHolder(StringHolder):
         if '..' in other:
             return ret
         return DependencyVariableString(ret)
+
+
+class OptionString(str):
+    optname: str
+
+    def __new__(cls, value: str, name: str) -> 'OptionString':
+        obj = str.__new__(cls, value)
+        obj.optname = name
+        return obj
+
+    def __getnewargs__(self) -> T.Tuple[str, str]: # type: ignore # because the entire point of this is to diverge
+        return (str(self), self.optname)
+
+
+class OptionStringHolder(StringHolder):
+    held_object: OptionString
+
+    def op_div(self, other: str) -> T.Union[str, OptionString]:
+        ret = super().op_div(other)
+        name = self._op_div(self.held_object.optname, other)
+        return OptionString(ret, name)