feat(cmake): add ixm_property command to the public runtime

docs/commands/common.md

@@ -21,8 +21,51 @@ set is whatever is passed after the `variable` argument (i.e., [`ARGN`][argn]).
 ### Required Parameters {#fallback/required}
 
 `variable`
+: *Type*: `identifier`
 : Name of the variable to store values in.
+
+## `ixm_property`
+
+Creates a generator expression for reading from a target property, as well as
+ensuring that any resulting values from said generator expression are also
+evaluated. Supports both the `$<TARGET_PROPERTY:target,property>` format, as
+well as `$<TARGET_PROPERTY:property>`.
+
+### Required Parameters {#property/required}
+
+`property`
 : *Type*: `identifier`
+: Name of the property to create the generator expression for.
+
+
+### Keyword Parameters {#property/required}
+
+`CONTEXT`
+: *Type*: `option`
+: Use `TARGET_GENEX_EVAL` instead of `GENEX_EVAL` for the generator expression.
+
+`TARGET`
+: *Type*: `target`
+: Name of target or a generator expression that evaluates to a target name.
+
+`OUTPUT_VARIABLE`
+: *Type*: `identifier`
+: *Default: `${property}`
+: Name of the variable to write the generator expression to.
+
+`PREFIX`
+: *Type*: `identifier[]`
+: Any number of identifiers to prefix to the property. These are joined via the
+  `_` character, and are most useful when the `OUTPUT_VARIABLE` argument isn't
+  used and the user wishes to use the provided `property` instead.
+
+### Example
+
+```cmake
+ixm_property(IMPORTED_LOCATION TARGET ccache::ccache)
+set_property(TARGET ${PROJECT_NAME} PROPERTY
+  CXX_COMPILER_LAUNCHER ${IMPORTED_LOCATION})
+```
 
 ## `ixm::unimplemented`
 

runtime/common.cmake

@@ -77,3 +77,36 @@ function (ixm_fallback variable)
     set(${variable} ${ARGN} PARENT_SCOPE)
   endif()
 endfunction()
+#[============================================================================[
+# @summary Creates a generator expression for reading from a target property.
+# @description This command permits creating generator expressions for targets
+# that are *not yet defined*, even if the `TARGET` parameter is passed in.
+#
+# @param {identifier} property - Name of the property to create generator
+# expression for.
+# @param {option} [CONTEXT] - Use `TARGET_GENEX_EVAL` instead of `GENEX_EVAL`.
+# Does nothing if `TARGET` has not been specified.
+# @param {target} [TARGET] - Name of a target to use for context and scope.
+# @param {identifier} [OUTPUT_VARIABLE=${property}] - Name of the variable to
+# output.
+# @param {list} [PREFIX] - Additional prefixes to prepend to the property.
+# These are joined via the `_` character. Useful if `OUTPUT_VARIABLE` is not
+# provided, as this allows for more complex property generator expressions with
+# simple output variables.
+#]============================================================================]
+function (ixm_property property)
+  cmake_parse_arguments(PARSE_ARGV 1 ARG "CONTEXT" "TARGET;OUTPUT_VARIABLE" "PREFIX")
+  ixm_fallback(ARG_OUTPUT_VARIABLE ${property})
+  string(JOIN _ property ${ARG_PREFIX} ${property})
+
+  set(eval GENEX_EVAL:)
+  set(target)
+  if (ARG_TARGET)
+    set(target "${ARG_TARGET},") # note the `,` at the end of the string
+    if (ARG_CONTEXT)
+      set(eval TARGET_GENEX_EVAL:${target})
+    endif()
+  endif()
+
+  set(${ARG_OUTPUT_VARIABLE} "$<${eval}$<TARGET_PROPERTY:${target}${property}>>" PARENT_SCOPE)
+endfunction()