Auto merge of #23289 - mihneadb:rustdoc-search-by-type, r=alexcrichton

This adds search by type (for functions/methods) support to Rustdoc. Target issue is at https://github.com/rust-lang/rfcs/issues/658.

I've described my approach here: https://github.com/rust-lang/rfcs/issues/658#issuecomment-76484200. I'll copy the text in here as well:

---

Hi, it took me longer than I wished, but I have implemented this in a not-too-complex way that I think can be extended to support more complex features (like the ones mentioned [here](https://github.com/rust-lang/rust/issues/12866#issuecomment-66945317)).

The idea is to generate a JSON representation of the types of methods/functions in the existing index, and then make the JS understand when it should look by type (and not by name).

I tried to come up with a JSON representation that can be extended to support generics, bounds, ref/mut annotations and so on. Here are a few samples:

Function:

```rust
fn to_uppercase(c: char) -> char
```

```json
{
    "inputs": [
        {"name": "char"}
    ],
    "output": {
        "name": "char",
    }
}
```

Method (implemented or defined in trait):

```rust
// in struct Vec
// self is considered an argument as well
fn capacity(&self) -> usize
```

```json
{
    "inputs": [
        {"name": "vec"}
    ],
    "output": {
        "name": "usize"
    }
}
```

This simple format can be extended by adding more fields, like `generic: bool`, a `bounds` mapping and so on.

I have a working implementation in https://github.com/rust-lang/rust/compare/master...mihneadb:rustdoc-search-by-type. You can check out a live demo [here](http://data.mihneadb.net/doc/std/index.html?search=charext%20-%3E%20char).

![screenshot from 2015-02-28 00 54 00](https://cloud.githubusercontent.com/assets/643127/6422722/7e5374ee-bee4-11e4-99a6-9aac3c9d5068.png)


The feature list is not that long:
- search by types (you *can* use generics as well, as long as you use the exact name - e.g. [`vec,t -> `](http://data.mihneadb.net/doc/std/index.html?search=vec%2C%20t%20-%3E))
- order of arguments does not matter
- `self` is took into account as well (e.g. search for `vec -> usize`)
- does not use "complex" annotations (e.g. you don't search for `&char -> char` but for `char -> char`)

My goal is to get a working, minimal "base" merged so that others can build upon it. How should I proceed? Do I open a PR (badly in need of code review since this is my first non "hello world"-ish rust code)?

---

src/librustdoc/html/static/main.js

@@ -209,6 +209,33 @@
                         break;
                     }
                 }
+            // searching by type
+            } else if (val.search("->") > -1) {
+                var trimmer = function (s) { return s.trim(); };
+                var parts = val.split("->").map(trimmer);
+                var input = parts[0];
+                // sort inputs so that order does not matter
+                var inputs = input.split(",").map(trimmer).sort();
+                var output = parts[1];
+
+                for (var i = 0; i < nSearchWords; ++i) {
+                    var type = searchIndex[i].type;
+                    if (!type) {
+                        continue;
+                    }
+
+                    // sort index inputs so that order does not matter
+                    var typeInputs = type.inputs.map(function (input) {
+                        return input.name;
+                    }).sort();
+
+                    // allow searching for void (no output) functions as well
+                    var typeOutput = type.output ? type.output.name : "";
+                    if (inputs.toString() === typeInputs.toString() &&
+                        output == typeOutput) {
+                        results.push({id: i, index: -1, dontValidate: true});
+                    }
+                }
             } else {
                 // gather matching search results up to a certain maximum
                 val = val.replace(/\_/g, "");
@@ -329,6 +356,11 @@
                     path = result.item.path.toLowerCase(),
                     parent = result.item.parent;
 
+                // this validation does not make sense when searching by types
+                if (result.dontValidate) {
+                    continue;
+                }
+
                 var valid = validateResult(name, path, split, parent);
                 if (!valid) {
                     result.id = -1;
@@ -573,7 +605,8 @@
                 //              (String) name,
                 //              (String) full path or empty string for previous path,
                 //              (String) description,
-                //              (optional Number) the parent path index to `paths`]
+                //              (Number | null) the parent path index to `paths`]
+                //              (Object | null) the type of the function (if any)
                 var items = rawSearchIndex[crate].items;
                 // an array of [(Number) item type,
                 //              (String) name]
@@ -598,7 +631,7 @@
                     var rawRow = items[i];
                     var row = {crate: crate, ty: rawRow[0], name: rawRow[1],
                                path: rawRow[2] || lastPath, desc: rawRow[3],
-                               parent: paths[rawRow[4]]};
+                               parent: paths[rawRow[4]], type: rawRow[5]};
                     searchIndex.push(row);
                     if (typeof row.name === "string") {
                         var word = row.name.toLowerCase();