Improve error messages and reporting in GN

tools/gn/builder.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/builder.h"
 
 #include "tools/gn/config.h"
 #include "tools/gn/err.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/scheduler.h"
@@ skipping 240 matching lines @@
   if (!record) {
     // Not seen this record yet, create a new one.
     record = new BuilderRecord(type, label);
     record->set_originally_referenced_from(request_from);
     records_[label] = record;
     return record;
   }
 
   // Check types.
   if (record->type() != type) {
-    *err = Err(request_from, "Item type does not match.",
-        "The item \"" + label.GetUserVisibleName(false) +
-        "\"\nwas expected to be a " +
-        BuilderRecord::GetNameForType(type) +
-        " but was previously referenced as a " +
-        BuilderRecord::GetNameForType(record->type()));
+    std::string msg =
+        "The type of " + label.GetUserVisibleName(false) +
+        "\nhere is a " + BuilderRecord::GetNameForType(type) +
+        " but was previously seen as a " +
+        BuilderRecord::GetNameForType(record->type()) + ".\n\n"
+        "The most common cause is that the label of a config was put in the\n"
+        "in the deps section of a target (or vice-versa).";
+    *err = Err(request_from, "Item type does not match.", msg);
     if (record->originally_referenced_from()) {
       err->AppendSubErr(Err(record->originally_referenced_from(),
-                            "The previous reference was here."));
+                            std::string()));
     }
     return NULL;
   }
 
   return record;
 }
 
 BuilderRecord* Builder::GetResolvedRecordOfType(const Label& label,
                                                 const ParseNode* origin,
                                                 BuilderRecord::ItemType type,
@@ skipping 74 matching lines @@
        i != deps.end(); i++) {
     BuilderRecord* cur = *i;
     if (!cur->should_generate()) {
       ScheduleItemLoadIfNecessary(cur);
       RecursiveSetShouldGenerate(cur, false);
     }
   }
 }
 
 void Builder::ScheduleItemLoadIfNecessary(BuilderRecord* record) {
-  loader_->Load(record->label());
+  const ParseNode* origin = record->originally_referenced_from();
+  loader_->Load(record->label(),
+                origin ? origin->GetRange() : LocationRange());
 }
 
 bool Builder::ResolveItem(BuilderRecord* record, Err* err) {
   DCHECK(record->can_resolve() && !record->resolved());
 
   if (record->type() == BuilderRecord::ITEM_TARGET) {
     Target* target = record->item()->AsTarget();
     if (!ResolveDeps(&target->deps(), err) ||
         !ResolveDeps(&target->datadeps(), err) ||
         !ResolveConfigs(&target->configs(), err) ||
@@ skipping 91 matching lines @@
   // Walk backwards since the dependency arrows point in the reverse direction.
   std::string ret;
   for (int i = static_cast<int>(cycle.size()) - 1; i >= 0; i--) {
     ret += "  " + cycle[i]->label().GetUserVisibleName(false);
     if (i != 0)
       ret += " ->\n";
   }
 
   return ret;
 }