Better handling of initial indent at file start.

* Detect initial indentation before the first token and enforce it.
  * Don't add `INDENT` token (or the matching `OUTDENT, TERMINATOR`).

lib/coffee-script/grammar.js

@@ -32,7 +32,7 @@
     Root: [
       o('', function() {
         return new Block;
-      }), o('Body'), o('Block TERMINATOR')
+      }), o('Body')
     ],
     Body: [
       o('Line', function() {

lib/coffee-script/lexer.js

@@ -17,6 +17,7 @@
       }
       this.literate = opts.literate;
       this.indent = 0;
+      this.baseIndent = 0;
       this.indebt = 0;
       this.outdebt = 0;
       this.indents = [];
@@ -346,11 +347,17 @@
           this.suppressNewlines();
           return indent.length;
         }
+        if (!this.tokens.length) {
+          this.baseIndent = this.indent = size;
+          return indent.length;
+        }
         diff = size - this.indent + this.outdebt;
         this.token('INDENT', diff, indent.length - size, size);
         this.indents.push(diff);
         this.ends.push('OUTDENT');
         this.outdebt = this.indebt = 0;
+      } else if (size < this.baseIndent) {
+        this.error('missing indentation', indent.length);
       } else {
         this.indebt = 0;
         this.outdentToken(this.indent - size, noNewlines, indent.length);
@@ -774,10 +781,15 @@
       return quote + this.escapeLines(body, heredoc) + quote;
     };
 
-    Lexer.prototype.error = function(message) {
+    Lexer.prototype.error = function(message, offset) {
+      var first_column, first_line, _ref2;
+      if (offset == null) {
+        offset = 0;
+      }
+      _ref2 = this.getLineAndColumnFromChunk(offset), first_line = _ref2[0], first_column = _ref2[1];
       return throwSyntaxError(message, {
-        first_line: this.chunkLine,
-        first_column: this.chunkColumn
+        first_line: first_line,
+        first_column: first_column
       });
     };
 

src/grammar.coffee

@@ -74,7 +74,6 @@ grammar =
   Root: [
     o '',                                       -> new Block
     o 'Body'
-    o 'Block TERMINATOR'
   ]
 
   # Any list of statements and expressions, separated by line breaks or semicolons.

src/lexer.coffee

@@ -35,13 +35,14 @@ exports.Lexer = class Lexer
   # Before returning the token stream, run it through the [Rewriter](rewriter.html)
   # unless explicitly asked not to.
   tokenize: (code, opts = {}) ->
-    @literate = opts.literate  # Are we lexing literate CoffeeScript?
-    @indent   = 0              # The current indentation level.
-    @indebt   = 0              # The over-indentation at the current level.
-    @outdebt  = 0              # The under-outdentation at the current level.
-    @indents  = []             # The stack of all current indentation levels.
-    @ends     = []             # The stack for pairing up tokens.
-    @tokens   = []             # Stream of parsed tokens in the form `['TYPE', value, location data]`.
+    @literate   = opts.literate  # Are we lexing literate CoffeeScript?
+    @indent     = 0              # The current indentation level.
+    @baseIndent = 0              # The overall minimum indentation level
+    @indebt     = 0              # The over-indentation at the current level.
+    @outdebt    = 0              # The under-outdentation at the current level.
+    @indents    = []             # The stack of all current indentation levels.
+    @ends       = []             # The stack for pairing up tokens.
+    @tokens     = []             # Stream of parsed tokens in the form `['TYPE', value, location data]`.
 
     @chunkLine =
         opts.line or 0         # The start line for the current @chunk.
@@ -322,11 +323,16 @@ exports.Lexer = class Lexer
         @indebt = size - @indent
         @suppressNewlines()
         return indent.length
+      unless @tokens.length
+        @baseIndent = @indent = size
+        return indent.length
       diff = size - @indent + @outdebt
       @token 'INDENT', diff, indent.length - size, size
       @indents.push diff
       @ends.push 'OUTDENT'
       @outdebt = @indebt = 0
+    else if size < @baseIndent
+      @error 'missing indentation', indent.length
     else
       @indebt = 0
       @outdentToken @indent - size, noNewlines, indent.length
@@ -691,10 +697,11 @@ exports.Lexer = class Lexer
     quote + @escapeLines(body, heredoc) + quote
 
   # Throws a compiler error on the current position.
-  error: (message) ->
+  error: (message, offset = 0) ->
     # TODO: Are there some cases we could improve the error line number by
     # passing the offset in the chunk where the error happened?
-    throwSyntaxError message, first_line: @chunkLine, first_column: @chunkColumn
+    [first_line, first_column] = @getLineAndColumnFromChunk offset
+    throwSyntaxError message, {first_line, first_column}
 
 # Constants
 # ---------

test/formatting.coffee

@@ -144,3 +144,10 @@ test "#1299: Disallow token misnesting", ->
     ok no
   catch e
     eq 'unmatched ]', e.message
+
+test "#2981: Enforce initial indentation", ->
+  try
+    CoffeeScript.compile '  a\nb'
+    ok no
+  catch e
+    eq 'missing indentation', e.message

test/location.coffee

@@ -41,8 +41,8 @@ test "Verify location of generated tokens", ->
 test "Verify location of generated tokens (with indented first line)", ->
   tokens = CoffeeScript.tokens "  a = 83"
 
-  eq tokens.length, 6
-  [IndentToken, aToken, equalsToken, numberToken] = tokens
+  eq tokens.length, 4
+  [aToken, equalsToken, numberToken] = tokens
 
   eq aToken[2].first_line, 0
   eq aToken[2].first_column, 2