multi line error highlights

Reference: #1131

Signed-off-by: Anurag Soni <anuragsoni.13@gmail.com>

CHANGES.md

@@ -19,6 +19,7 @@ next
 
 - Fix parsing `ocamllex` stanza in jbuild files (#1150, @rgrinberg)
 
+- Highlight multi-line errors (#1131, @anuragsoni)
 
 1.1.1 (08/08/2018)
 ------------------

src/loc.ml

@@ -70,10 +70,27 @@ let file_line path n =
       input_line ic
     )
 
+let file_lines path ~start ~stop =
+  Io.with_file_in ~binary:true path
+    ~f:(fun ic ->
+      let rec aux acc lnum =
+        if lnum > stop then
+          List.rev acc
+        else if lnum < start then
+          (ignore (input_line ic);
+           aux acc (lnum + 1))
+        else
+          let line = input_line ic in
+          aux ((string_of_int lnum, line) :: acc) (lnum + 1)
+      in
+      aux [] 1
+    )
+
 let print ppf loc =
   let { start; stop } = loc in
   let start_c = start.pos_cnum - start.pos_bol in
   let stop_c  = stop.pos_cnum  - start.pos_bol in
+  let num_lines = stop.pos_lnum - start.pos_lnum in
   let pp_file_excerpt pp () =
     let whole_file = start_c = 0 && stop_c = 0 in
     if not whole_file then
@@ -85,6 +102,14 @@ let print ppf loc =
           Format.fprintf pp "%s\n%*s\n" line
             stop_c
             (String.make len '^')
+        else if num_lines <= 10 then
+          let lines = file_lines path ~start:start.pos_lnum ~stop:stop.pos_lnum in
+          let last_lnum = Option.map ~f:fst (List.last lines) in
+          let padding_width = Option.value_exn
+                                (Option.map ~f:String.length last_lnum) in
+          List.iter ~f:(fun (lnum, l) ->
+            Format.fprintf pp "%*s: %s\n" padding_width lnum l)
+          lines
   in
   Format.fprintf ppf
     "@{<loc>File \"%s\", line %d, characters %d-%d:@}@\n%a"

test/blackbox-tests/test-cases/intf-only/run.t

@@ -24,6 +24,8 @@ Errors:
   $ dune build --display short --root a foo.cma
   Entering directory 'a'
   File "dune", line 1, characters 0-21:
+  1: (library
+  2:  (name foo))
   Warning: Some modules don't have an implementation.
   You need to add the following field to this stanza:
   

test/blackbox-tests/test-cases/missing-loc-run/run.t

@@ -3,6 +3,9 @@ Exact path provided by the user:
   $ dune runtest --root precise-path
   Entering directory 'precise-path'
   File "dune", line 1, characters 0-49:
+  1: (alias
+  2:  (name runtest)
+  3:  (action (run ./foo.exe)))
   Error: No rule found for foo.exe
   [1]
 
@@ -21,5 +24,8 @@ Path in deps field of alias stanza
   $ dune runtest --root alias-deps-field
   Entering directory 'alias-deps-field'
   File "dune", line 1, characters 0-38:
+  1: (alias
+  2:  (name runtest)
+  3:  (deps foobar))
   Error: No rule found for foobar
   [1]

test/blackbox-tests/test-cases/no-installable-mode/run.t

@@ -3,6 +3,11 @@ message is displayed:
 
   $ dune build --root=public --display=short
   File "jbuild", line 4, characters 2-74:
+  4:   (
+  5:    (name mylib)
+  6:    (public_name mylib)
+  7:    (modes (shared_object))
+  8:    )
   Error: No installable mode found for this executable.
   One of the following modes is required:
    - exe

test/blackbox-tests/test-cases/several-packages/run.t

@@ -5,6 +5,9 @@ displayed. This can happen for:
 
   $ dune build --root executable
   File "dune", line 1, characters 0-43:
+  1: (executable
+  2:   (public_name an_executable)
+  3: )
   Error: I can't determine automatically which package this stanza is for.
   I have the choice between these ones:
   - pkg1 (because of pkg1.opam)
@@ -29,6 +32,10 @@ displayed. This can happen for:
 
   $ dune build --root install
   File "dune", line 1, characters 0-44:
+  1: (install
+  2:  (section etc)
+  3:  (files file.conf)
+  4: )
   Error: I can't determine automatically which package this stanza is for.
   I have the choice between these ones:
   - pkg1 (because of pkg1.opam)

test/blackbox-tests/test-cases/too-many-parens/d/dune

@@ -0,0 +1,15 @@
+(executable
+  (name hello)
+  (libraries (a
+              b
+              c
+              d
+              e
+              f
+              g
+              h
+              i
+              j
+              k
+              l)
+  ))

test/blackbox-tests/test-cases/too-many-parens/d/dune-project

@@ -0,0 +1 @@
+(lang dune 1.0)

test/blackbox-tests/test-cases/too-many-parens/run.t

@@ -3,6 +3,11 @@ are readable.
 
   $ dune build --root a
   File "dune", line 1, characters 12-72:
+  1: (executable (
+  2:   (name hello)
+  3:   (public_name hello)
+  4:   (libraries (lib))
+  5: ))
   These parentheses are no longer necessary with dune, please remove them.
   [1]
 
@@ -19,3 +24,9 @@ are readable.
          ^^^^^^^
   These parentheses are no longer necessary with dune, please remove them.
   [1]
+
+Checking that extra long stanzas (over 10 lines) are not printed
+  $ dune build --root d
+  File "dune", line 3, characters 13-192:
+  These parentheses are no longer necessary with dune, please remove them.
+  [1]