1 files changed, 47 insertions, 12 deletions

diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index 2f6b361bb..f7a3ec3a0 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -31,11 +31,25 @@ struct CmdWhyDepends : SourceExprCommand
 {
     std::string _package, _dependency;
     bool all = false;
+    bool precise = false;
 
     CmdWhyDepends()
     {
-        expectArg("package", &_package);
-        expectArg("dependency", &_dependency);
+        expectArgs({
+            .label = "package",
+            .handler = {&_package},
+            .completer = {[&](size_t, std::string_view prefix) {
+                completeInstallable(prefix);
+            }}
+        });
+
+        expectArgs({
+            .label = "dependency",
+            .handler = {&_dependency},
+            .completer = {[&](size_t, std::string_view prefix) {
+                completeInstallable(prefix);
+            }}
+        });
 
         addFlag({
             .longName = "all",
@@ -43,6 +57,12 @@ struct CmdWhyDepends : SourceExprCommand
             .description = "Show all edges in the dependency graph leading from *package* to *dependency*, rather than just a shortest path.",
             .handler = {&all, true},
         });
+
+        addFlag({
+            .longName = "precise",
+            .description = "For each edge in the dependency graph, show the files in the parent that cause the dependency.",
+            .handler = {&precise, true},
+        });
     }
 
     std::string description() override
@@ -137,26 +157,28 @@ struct CmdWhyDepends : SourceExprCommand
            closure (i.e., that have a non-infinite distance to
            'dependency'). Print every edge on a path between `package`
            and `dependency`. */
-        std::function<void(Node &, const string &, const string &)> printNode;
+        std::function<void(Node &, const std::string &, const std::string &)> printNode;
 
         struct BailOut { };
 
-        printNode = [&](Node & node, const string & firstPad, const string & tailPad) {
+        printNode = [&](Node & node, const std::string & firstPad, const std::string & tailPad) {
             auto pathS = store->printStorePath(node.path);
 
             assert(node.dist != inf);
-            logger->cout("%s%s%s%s" ANSI_NORMAL,
-                firstPad,
-                node.visited ? "\e[38;5;244m" : "",
-                firstPad != "" ? "→ " : "",
-                pathS);
+            if (precise) {
+                logger->cout("%s%s%s%s" ANSI_NORMAL,
+                    firstPad,
+                    node.visited ? "\e[38;5;244m" : "",
+                    firstPad != "" ? "→ " : "",
+                    pathS);
+            }
 
             if (node.path == dependencyPath && !all
                 && packagePath != dependencyPath)
                 throw BailOut();
 
             if (node.visited) return;
-            node.visited = true;
+            if (precise) node.visited = true;
 
             /* Sort the references by distance to `dependency` to
                ensure that the shortest path is printed first. */
@@ -224,9 +246,8 @@ struct CmdWhyDepends : SourceExprCommand
 
             // FIXME: should use scanForReferences().
 
-            visitPath(pathS);
+            if (precise) visitPath(pathS);
 
-            RunPager pager;
             for (auto & ref : refs) {
                 std::string hash(ref.second->path.hashPart());
 
@@ -240,13 +261,27 @@ struct CmdWhyDepends : SourceExprCommand
                     if (!all) break;
                 }
 
+                if (!precise) {
+                    auto pathS = store->printStorePath(ref.second->path);
+                    logger->cout("%s%s%s%s" ANSI_NORMAL,
+                        firstPad,
+                        ref.second->visited ? "\e[38;5;244m" : "",
+                        last ? treeLast : treeConn,
+                        pathS);
+                    node.visited = true;
+                }
+
                 printNode(*ref.second,
                     tailPad + (last ? treeNull : treeLine),
                     tailPad + (last ? treeNull : treeLine));
             }
         };
 
+        RunPager pager;
         try {
+            if (!precise) {
+                logger->cout("%s", store->printStorePath(graph.at(packagePath).path));
+            }
             printNode(graph.at(packagePath), "", "");
         } catch (BailOut & ) { }
     }