Auto merge of #30064 - fhartwig:macro-suggestions, r=sanxiyn

Fixes #13677
This does the same sort of suggestion for misspelt macros that we already do for misspelt identifiers.
Example. Compiling this program:

```rust
macro_rules! foo {
    ($e:expr) => ( $e )
}

fn main() {
    fob!("hello!");
}
```

gives the following error message:

```
/Users/mcp/temp/test.rs:7:5: 7:8 error: macro undefined: 'fob!'
/Users/mcp/temp/test.rs:7     fob!("hello!");
                              ^~~
/Users/mcp/temp/test.rs:7:5: 7:8 help: did you mean `foo`?
/Users/mcp/temp/test.rs:7     fob!("hello!");
```

I had to move the levenshtein distance function into libsyntax for this. Maybe this should live somewhere else (some utility crate?), but I couldn't find a crate to put it in that is imported by libsyntax and the other rustc crates.

Author: bors

src/librustc/lib.rs

@@ -146,7 +146,6 @@ pub mod util {
     pub mod common;
     pub mod ppaux;
     pub mod nodemap;
-    pub mod lev_distance;
     pub mod num;
     pub mod fs;
 }

src/librustc_resolve/lib.rs

@@ -62,7 +62,6 @@ use rustc::middle::privacy::*;
 use rustc::middle::subst::{ParamSpace, FnSpace, TypeSpace};
 use rustc::middle::ty::{Freevar, FreevarMap, TraitMap, GlobMap};
 use rustc::util::nodemap::{NodeMap, DefIdSet, FnvHashMap};
-use rustc::util::lev_distance::lev_distance;
 
 use syntax::ast;
 use syntax::ast::{CRATE_NODE_ID, Ident, Name, NodeId, CrateNum, TyIs, TyI8, TyI16, TyI32, TyI64};
@@ -72,6 +71,7 @@ use syntax::ext::mtwt;
 use syntax::parse::token::{self, special_names, special_idents};
 use syntax::ptr::P;
 use syntax::codemap::{self, Span, Pos};
+use syntax::util::lev_distance::{lev_distance, max_suggestion_distance};
 
 use rustc_front::intravisit::{self, FnKind, Visitor};
 use rustc_front::hir;
@@ -3383,11 +3383,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
         }
 
-        // As a loose rule to avoid obviously incorrect suggestions, clamp the
-        // maximum edit distance we will accept for a suggestion to one third of
-        // the typo'd name's length.
-        let max_distance = std::cmp::max(name.len(), 3) / 3;
-
+        let max_distance = max_suggestion_distance(name);
         if !values.is_empty() && values[smallest] <= max_distance && name != &maybes[smallest][..] {
 
             SuggestionType::Function(maybes[smallest].to_string())

src/librustc_typeck/check/mod.rs

@@ -110,7 +110,6 @@ use TypeAndSubsts;
 use lint;
 use util::common::{block_query, ErrorReported, indenter, loop_query};
 use util::nodemap::{DefIdMap, FnvHashMap, NodeMap};
-use util::lev_distance::lev_distance;
 
 use std::cell::{Cell, Ref, RefCell};
 use std::collections::{HashSet};
@@ -123,6 +122,7 @@ use syntax::codemap::{self, Span, Spanned};
 use syntax::owned_slice::OwnedSlice;
 use syntax::parse::token::{self, InternedString};
 use syntax::ptr::P;
+use syntax::util::lev_distance::lev_distance;
 
 use rustc_front::intravisit::{self, Visitor};
 use rustc_front::hir;

src/libsyntax/ext/base.rs

@@ -24,6 +24,7 @@ use parse::token;
 use parse::token::{InternedString, intern, str_to_ident};
 use ptr::P;
 use util::small_vector::SmallVector;
+use util::lev_distance::{lev_distance, max_suggestion_distance};
 use ext::mtwt;
 use fold::Folder;
 
@@ -776,6 +777,20 @@ impl<'a> ExtCtxt<'a> {
     pub fn name_of(&self, st: &str) -> ast::Name {
         token::intern(st)
     }
+
+    pub fn suggest_macro_name(&mut self, name: &str, span: Span) {
+        let mut min: Option<(Name, usize)> = None;
+        let max_dist = max_suggestion_distance(name);
+        for macro_name in self.syntax_env.names.iter() {
+            let dist = lev_distance(name, &macro_name.as_str());
+            if dist <= max_dist && (min.is_none() || min.unwrap().1 > dist) {
+                min = Some((*macro_name, dist));
+            }
+        }
+        if let Some((suggestion, _)) = min {
+            self.fileline_help(span, &format!("did you mean `{}!`?", suggestion));
+        }
+    }
 }
 
 /// Extract a string literal from the macro expanded version of `expr`,

src/libsyntax/ext/expand.rs

@@ -191,6 +191,7 @@ fn expand_mac_invoc<T, F, G>(mac: ast::Mac,
                 pth.span,
                 &format!("macro undefined: '{}!'",
                         &extname));
+            fld.cx.suggest_macro_name(&extname.as_str(), pth.span);
 
             // let compilation continue
             None

src/libsyntax/lib.rs

@@ -65,6 +65,7 @@ macro_rules! panictry {
 
 pub mod util {
     pub mod interner;
+    pub mod lev_distance;
     pub mod node_count;
     pub mod parser;
     #[cfg(test)]

src/librustc/util/lev_distance.rs renamed to src/libsyntax/util/lev_distance.rs

@@ -41,6 +41,14 @@ pub fn lev_distance(me: &str, t: &str) -> usize {
     dcol[t_last + 1]
 }
 
+pub fn max_suggestion_distance(name: &str) -> usize {
+    use std::cmp::max;
+    // As a loose rule to avoid obviously incorrect suggestions, clamp the
+    // maximum edit distance we will accept for a suggestion to one third of
+    // the typo'd name's length.
+    max(name.len(), 3) / 3
+}
+
 #[test]
 fn test_lev_distance() {
     use std::char::{ from_u32, MAX };

src/test/compile-fail/macro-name-typo.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    printlx!("oh noes!"); //~ ERROR macro undefined
+    //~^ HELP did you mean `println!`?
+}