FIX: Compose on Maps values that evaluate to a block expands the map.

Related to: Oldes/Rebol-issues#2686

Author: rgchris

src/core/c-do.c

@@ -1399,8 +1399,8 @@ x*/	static REBINT Do_Args_Light(REBVAL *func, REBVAL *path, REBSER *block, REBCN
 			DSP++; // !!!DSP temp
 			if (THROWN(DS_TOP)) return;
 
-			// If result is a block, and not /only, insert its contents:
-			if (IS_BLOCK(DS_TOP) && !only) {
+			// If result is a block, and not /only or a map value, insert its contents:
+			if (IS_BLOCK(DS_TOP) && !only && !IS_MAP(block)) {
 				// Append series to the stack:
 				SERIES_TAIL(DS_Series) = DSP; // overwrites TOP value
 				Append_Series(DS_Series, (REBYTE *)VAL_BLK_DATA(DS_TOP), VAL_BLK_LEN(DS_TOP));

src/tests/units/evaluation-test.r3

@@ -505,6 +505,9 @@ Rebol [
 	--assert #[num: 4] = use[v][v: 4 compose #[num: (v)]]
 	--assert #[num: 5] = apply func [val] [compose/deep #[num: (val)]] [5]
 
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2686
+	--assert #[num: [one two three]] = compose #[num: ([one two three])]
+
 ===end-group===
 
 ===start-group=== "unset value passing"