Mustachio: Implement and use key spans (#2519)

Mustachio: Implement and use key spans

Author: srawlins

lib/src/mustachio/parser.dart

@@ -177,8 +177,9 @@ class MustachioParser {
     _index += 2;
 
     var key = template.substring(startIndex, endIndex);
-    return _TagParseResult.ok(
-        Partial(key, span: _sourceFile.span(tagStartIndex, _index)));
+    var keySpan = _sourceFile.span(startIndex, endIndex);
+    return _TagParseResult.ok(Partial(key,
+        span: _sourceFile.span(tagStartIndex, _index), keySpan: keySpan));
   }
 
   /// Tries to parse a section tag at [_index].
@@ -208,20 +209,30 @@ class MustachioParser {
       // inside the section, are the children of the [three] section. The
       // [three] section is the singular child node of the [two] section, and
       // the [two] section is the singular child of the [one] section.
-      var section =
-          Section([parsedKey.names.last], children, invert: invert, span: span);
-      for (var sectionKey in parsedKey.names.reversed.skip(1)) {
+      var lastName = parsedKey.names.last;
+      var keySpanEndOffset = parsedKey.span.end.offset;
+      var lastNameSpan = _sourceFile.span(
+          keySpanEndOffset - lastName.length, keySpanEndOffset);
+      var section = Section([lastName], children,
+          invert: invert, span: span, keySpan: lastNameSpan);
+      //for (var sectionKey in parsedKey.names.reversed.skip(1)) {
+      for (var i = parsedKey.names.length - 2; i >= 0; i--) {
+        var sectionKey = parsedKey.names[i];
+        // To find the start offset of the ith name, take the length of all of
+        // the names 0 through `i - 1` re-joined with '.', and a final '.' at
+        // the end.
+        var sectionKeyStartOffset = parsedKey.span.start.offset +
+            (i == 0 ? 0 : parsedKey.names.take(i).join('.').length + 1);
+        var keySpan = _sourceFile.span(
+            sectionKeyStartOffset, sectionKeyStartOffset + sectionKey.length);
         section = Section([sectionKey], [section],
-            invert: false,
-            // TODO(srawlins): It may not make sense to use [span] here; we
-            // might want to do the work to find the span of [sectionKey].
-            span: span);
+            invert: false, span: span, keySpan: keySpan);
       }
       return _TagParseResult.ok(section);
     }
 
-    return _TagParseResult.ok(
-        Section(parsedKey.names, children, invert: invert, span: span));
+    return _TagParseResult.ok(Section(parsedKey.names, children,
+        invert: invert, span: span, keySpan: parsedKey.span));
   }
 
   /// Tries to parse an end tag at [_index].
@@ -257,8 +268,9 @@ class MustachioParser {
       return _TagParseResult.endOfFile;
     }
 
+    var span = _sourceFile.span(tagStartIndex, _index);
     return _TagParseResult.ok(Variable(parsedKey.names,
-        escape: escape, span: _sourceFile.span(tagStartIndex, _index)));
+        escape: escape, span: span, keySpan: parsedKey.span));
   }
 
   /// Tries to parse a key at [_index].
@@ -289,6 +301,7 @@ class MustachioParser {
     }
 
     var key = template.substring(startIndex, _index);
+    var span = _sourceFile.span(startIndex, _index);
 
     if (key.length > 1 &&
         (key.codeUnitAt(0) == $dot || key.codeUnitAt(key.length - 1) == $dot)) {
@@ -306,7 +319,7 @@ class MustachioParser {
     if (escape) {
       if (char0 == $rbrace && char1 == $rbrace) {
         _index += 2;
-        return _KeyParseResult(_KeyParseResultType.parsedKey, key);
+        return _KeyParseResult(_KeyParseResultType.parsedKey, key, span: span);
       } else {
         return _KeyParseResult.notKey;
       }
@@ -318,7 +331,7 @@ class MustachioParser {
       var char2 = _nextNextChar;
       if (char0 == $rbrace && char1 == $rbrace && char2 == $rbrace) {
         _index += 3;
-        return _KeyParseResult(_KeyParseResultType.parsedKey, key);
+        return _KeyParseResult(_KeyParseResultType.parsedKey, key, span: span);
       } else {
         return _KeyParseResult.notKey;
       }
@@ -391,7 +404,10 @@ class Variable implements MustachioNode {
   @override
   final SourceSpan span;
 
-  Variable(this.key, {@required this.escape, @required this.span});
+  final SourceSpan keySpan;
+
+  Variable(this.key,
+      {@required this.escape, @required this.span, @required this.keySpan});
 
   @override
   String toString() => 'Variable[$key, escape=$escape]';
@@ -410,8 +426,10 @@ class Section implements MustachioNode {
   @override
   final SourceSpan span;
 
+  final SourceSpan keySpan;
+
   Section(this.key, this.children,
-      {@required this.invert, @required this.span});
+      {@required this.invert, @required this.span, @required this.keySpan});
 
   @override
   String toString() => 'Section[$key, invert=$invert]';
@@ -425,7 +443,9 @@ class Partial implements MustachioNode {
   @override
   final SourceSpan span;
 
-  Partial(this.key, {@required this.span});
+  final SourceSpan keySpan;
+
+  Partial(this.key, {@required this.span, @required this.keySpan});
 }
 
 /// An enumeration of types of tag parse results.
@@ -490,13 +510,18 @@ class _KeyParseResult {
 
   final List<String> names;
 
-  const _KeyParseResult._(this.type, this.names);
+  /// The source span from where this key was parsed, if this represents a
+  /// parsed key, othwerwise `null`.
+  final SourceSpan /*?*/ span;
+
+  const _KeyParseResult._(this.type, this.names, {this.span});
 
-  factory _KeyParseResult(_KeyParseResultType type, String key) {
+  factory _KeyParseResult(_KeyParseResultType type, String key,
+      {@required SourceSpan span}) {
     if (key == '.') {
-      return _KeyParseResult._(type, [key]);
+      return _KeyParseResult._(type, [key], span: span);
     } else {
-      return _KeyParseResult._(type, key.split('.'));
+      return _KeyParseResult._(type, key.split('.'), span: span);
     }
   }
 

lib/src/mustachio/renderer_base.dart

@@ -164,9 +164,8 @@ abstract class RendererBase<T> {
   /// [names] may have multiple dot-separate names, and [names] may not be a
   /// valid property of _this_ context type, in which the [parent] renderer is
   /// referenced.
-  // TODO(srawlins): Accept the [MustachioNode] here, so that the various errors
-  // can use the span.
-  String getFields(List<String> names) {
+  String getFields(Variable node) {
+    var names = node.key;
     if (names.length == 1 && names.single == '.') {
       return context.toString();
     }
@@ -178,18 +177,18 @@ abstract class RendererBase<T> {
       } on PartialMustachioResolutionError catch (e) {
         // The error thrown by [Property.renderVariable] does not have all of
         // the names required for a decent error. We throw a new error here.
-        throw MustachioResolutionError(
+        throw MustachioResolutionError(node.keySpan.message(
             "Failed to resolve '${e.name}' on ${e.contextType} while resolving "
             '$remainingNames as a property chain on any types in the context '
             "chain: $contextChainString, after first resolving '${names.first}' "
-            'to a property on $T');
+            'to a property on $T'));
       }
     } else if (parent != null) {
-      return parent.getFields(names);
+      return parent.getFields(node);
     } else {
-      throw MustachioResolutionError(
-          'Failed to resolve ${names.first} as a property on any types in the '
-          'context chain: $contextChainString');
+      throw MustachioResolutionError(node.keySpan.message(
+          "Failed to resolve '${names.first}' as a property on any types in the "
+          'context chain: $contextChainString'));
     }
   }
 
@@ -199,7 +198,7 @@ abstract class RendererBase<T> {
       if (node is Text) {
         write(node.content);
       } else if (node is Variable) {
-        var content = getFields(node.key);
+        var content = getFields(node);
         write(content);
       } else if (node is Section) {
         section(node);
@@ -214,10 +213,9 @@ abstract class RendererBase<T> {
     var property = getProperty(key);
     if (property == null) {
       if (parent == null) {
-        // TODO(srawlins): use the span of the key of [node] when implemented.
-        throw MustachioResolutionError(
-            'Failed to resolve $key as a property on any types in the current '
-            'context');
+        throw MustachioResolutionError(node.keySpan.message(
+            "Failed to resolve '$key' as a property on any types in the current "
+            'context'));
       } else {
         return parent.section(node);
       }
@@ -277,12 +275,13 @@ class SimpleRenderer extends RendererBase<Object> {
   Property<Object> getProperty(String key) => null;
 
   @override
-  String getFields(List<String> keyParts) {
-    if (keyParts.length == 1 && keyParts.single == '.') {
+  String getFields(Variable node) {
+    var names = node.key;
+    if (names.length == 1 && names.single == '.') {
       return context.toString();
     }
     if (parent != null) {
-      return parent.getFields(keyParts);
+      return parent.getFields(node);
     } else {
       return 'null';
     }