fix: refactor @base expansionLogic

Author: tplooker

lib/context.js

@@ -1069,50 +1069,30 @@ function _expandIri(activeCtx, value, relativeTo, localCtx, defined, options) {
       // the null case preserves value as potentially relative
       value = prependedResult;
     }
-  } else if(relativeTo.base && '@base' in activeCtx) {
+  } else if(relativeTo.base) {
     // prepend base
-    if(activeCtx['@base']) {
-      const prependedResult = prependBase(
-        prependBase(options.base, activeCtx['@base']), value);
-
-      let expansionMapResult = undefined;
-      if(options && options.expansionMap) {
-        // if we are about to expand the value by prepending
-        // @base then call the expansion map to inform
-        // interested callers that this is occurring
-
-        // TODO: use `await` to support async
-        expansionMapResult = options.expansionMap({
-          prependedIri: {
-            type: '@base',
-            base: activeCtx['@base'],
-            value,
-            result: prependedResult
-          },
-          activeCtx,
-          options
-        });
-      }
-      if(expansionMapResult !== undefined) {
-        value = expansionMapResult;
-      } else {
-        // the null case preserves value as potentially relative
-        value = prependedResult;
+    let prependedResult;
+    let expansionMapResult;
+    let base;
+    if('@base' in activeCtx) {
+      if(activeCtx['@base']) {
+        base = prependBase(options.base, activeCtx['@base']);
+        prependedResult = prependBase(base, value);
       }
+    } else {
+      base = options.base;
+      prependedResult = prependBase(options.base, value);
     }
-  } else if(relativeTo.base) {
-    const prependedResult = prependBase(options.base, value);
-    let expansionMapResult = undefined;
     if(options && options.expansionMap) {
-      // if we are about to expand the value by prepending
+      // if we are about to expand the value by pre-pending
       // @base then call the expansion map to inform
       // interested callers that this is occurring
 
       // TODO: use `await` to support async
       expansionMapResult = options.expansionMap({
         prependedIri: {
           type: '@base',
-          base: options.base,
+          base,
           value,
           result: prependedResult
         },
@@ -1122,7 +1102,8 @@ function _expandIri(activeCtx, value, relativeTo, localCtx, defined, options) {
     }
     if(expansionMapResult !== undefined) {
       value = expansionMapResult;
-    } else {
+    } else if(prependedResult !== undefined) {
+      // the null case preserves value as potentially relative
       value = prependedResult;
     }
   }