Highlight code in rustc --explain (WIP)

src/librustc_driver/Cargo.toml

@@ -32,6 +32,7 @@ rustc_resolve = { path = "../librustc_resolve" }
 rustc_save_analysis = { path = "../librustc_save_analysis" }
 rustc_trans = { path = "../librustc_trans" }
 rustc_typeck = { path = "../librustc_typeck" }
+rustc_highlight = { path = "../librustc_highlight" }
 serialize = { path = "../libserialize" }
 syntax = { path = "../libsyntax" }
 syntax_ext = { path = "../libsyntax_ext" }

src/librustc_driver/lib.rs

@@ -30,6 +30,7 @@
 #![feature(rustc_private)]
 #![feature(set_stdio)]
 #![feature(staged_api)]
+#![feature(rustc_highlight)]
 
 extern crate arena;
 extern crate flate;
@@ -53,6 +54,7 @@ extern crate rustc_resolve;
 extern crate rustc_save_analysis;
 extern crate rustc_trans;
 extern crate rustc_typeck;
+extern crate rustc_highlight;
 extern crate serialize;
 extern crate rustc_llvm as llvm;
 #[macro_use]
@@ -78,6 +80,7 @@ use rustc::lint::Lint;
 use rustc::lint;
 use rustc_metadata::locator;
 use rustc_metadata::cstore::CStore;
+use rustc_highlight::highlight::render_to_stdout_with_highlighting;
 use rustc::util::common::time;
 
 use serialize::json::ToJson;
@@ -349,6 +352,43 @@ pub trait CompilerCalls<'a> {
 #[derive(Copy, Clone)]
 pub struct RustcDefaultCalls;
 
+fn print_msg(text: &str) {
+    let mut code = String::new();
+    let mut in_code = false;
+    let mut code_is_rust = false;
+    for (i, line) in text.split('\n').enumerate() {
+        // Slice off the leading newline and print.
+        if i == 0 && line.len() == 0 {
+            continue;
+        }
+        if line.starts_with("```") {
+            if in_code {
+                if code_is_rust {
+                    println!("rust");
+                    render_to_stdout_with_highlighting(code);
+                } else {
+                    render_to_stdout_with_highlighting(code);
+                }
+                code = String::new();
+                code_is_rust = false;
+            } else {
+                if line.starts_with("```rust") {
+                    code_is_rust = true;
+                }
+            }
+            in_code = !in_code;
+            println!("```");
+        } else {
+            if in_code {
+                code.push_str(&line);
+                code.push_str("\n");
+            } else {
+                println!("{}", line);
+            }
+        }
+    }
+}
+
 fn handle_explain(code: &str,
                   descriptions: &errors::registry::Registry,
                   output: ErrorOutputType) {
@@ -359,14 +399,7 @@ fn handle_explain(code: &str,
     };
     match descriptions.find_description(&normalised) {
         Some(ref description) => {
-            // Slice off the leading newline and print.
-            print!("{}", &(&description[1..]).split("\n").map(|x| {
-                format!("{}\n", if x.starts_with("```") {
-                    "```"
-                } else {
-                    x
-                })
-            }).collect::<String>());
+            print_msg(description);
         }
         None => {
             early_error(output, &format!("no extended information for {}", code));

src/librustc_highlight/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "rustc_highlight"
+version = "0.0.0"
+
+[lib]
+name = "rustc_highlight"
+path = "lib.rs"
+crate-type = ["dylib"]
+
+[dependencies]
+syntax = { path = "../libsyntax" }
+syntax_pos = { path = "../libsyntax_pos" }
+log = { path = "../liblog" }