commentmap.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ast
     6  
     7  import (
     8  	"bytes"
     9  	"cmp"
    10  	"fmt"
    11  	"go/token"
    12  	"slices"
    13  	"strings"
    14  )
    15  
    16  // sortComments sorts the list of comment groups in source order.
    17  func sortComments(list []*CommentGroup) {
    18  	slices.SortFunc(list, func(a, b *CommentGroup) int {
    19  		return cmp.Compare(a.Pos(), b.Pos())
    20  	})
    21  }
    22  
    23  // A CommentMap maps an AST node to a list of comment groups
    24  // associated with it. See [NewCommentMap] for a description of
    25  // the association.
    26  type CommentMap map[Node][]*CommentGroup
    27  
    28  func (cmap CommentMap) addComment(n Node, c *CommentGroup) {
    29  	list := cmap[n]
    30  	if len(list) == 0 {
    31  		list = []*CommentGroup{c}
    32  	} else {
    33  		list = append(list, c)
    34  	}
    35  	cmap[n] = list
    36  }
    37  
    38  type byInterval []Node
    39  
    40  func (a byInterval) Len() int { return len(a) }
    41  func (a byInterval) Less(i, j int) bool {
    42  	pi, pj := a[i].Pos(), a[j].Pos()
    43  	return pi < pj || pi == pj && a[i].End() > a[j].End()
    44  }
    45  func (a byInterval) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
    46  
    47  // nodeList returns the list of nodes of the AST n in source order.
    48  func nodeList(n Node) []Node {
    49  	var list []Node
    50  	Inspect(n, func(n Node) bool {
    51  		// don't collect comments
    52  		switch n.(type) {
    53  		case nil, *CommentGroup, *Comment:
    54  			return false
    55  		}
    56  		list = append(list, n)
    57  		return true
    58  	})
    59  
    60  	// Note: The current implementation assumes that Inspect traverses the
    61  	//       AST in depth-first and thus _source_ order. If AST traversal
    62  	//       does not follow source order, the sorting call below will be
    63  	//       required.
    64  	// slices.Sort(list, func(a, b Node) int {
    65  	//       r := cmp.Compare(a.Pos(), b.Pos())
    66  	//       if r != 0 {
    67  	//               return r
    68  	//       }
    69  	//       return cmp.Compare(a.End(), b.End())
    70  	// })
    71  
    72  	return list
    73  }
    74  
    75  // A commentListReader helps iterating through a list of comment groups.
    76  type commentListReader struct {
    77  	fset     *token.FileSet
    78  	list     []*CommentGroup
    79  	index    int
    80  	comment  *CommentGroup  // comment group at current index
    81  	pos, end token.Position // source interval of comment group at current index
    82  }
    83  
    84  func (r *commentListReader) eol() bool {
    85  	return r.index >= len(r.list)
    86  }
    87  
    88  func (r *commentListReader) next() {
    89  	if !r.eol() {
    90  		r.comment = r.list[r.index]
    91  		r.pos = r.fset.Position(r.comment.Pos())
    92  		r.end = r.fset.Position(r.comment.End())
    93  		r.index++
    94  	}
    95  }
    96  
    97  // A nodeStack keeps track of nested nodes.
    98  // A node lower on the stack lexically contains the nodes higher on the stack.
    99  type nodeStack []Node
   100  
   101  // push pops all nodes that appear lexically before n
   102  // and then pushes n on the stack.
   103  func (s *nodeStack) push(n Node) {
   104  	s.pop(n.Pos())
   105  	*s = append((*s), n)
   106  }
   107  
   108  // pop pops all nodes that appear lexically before pos
   109  // (i.e., whose lexical extent has ended before or at pos).
   110  // It returns the last node popped.
   111  func (s *nodeStack) pop(pos token.Pos) (top Node) {
   112  	i := len(*s)
   113  	for i > 0 && (*s)[i-1].End() <= pos {
   114  		top = (*s)[i-1]
   115  		i--
   116  	}
   117  	*s = (*s)[0:i]
   118  	return top
   119  }
   120  
   121  // NewCommentMap creates a new comment map by associating comment groups
   122  // of the comments list with the nodes of the AST specified by node.
   123  //
   124  // A comment group g is associated with a node n if:
   125  //
   126  //   - g starts on the same line as n ends
   127  //   - g starts on the line immediately following n, and there is
   128  //     at least one empty line after g and before the next node
   129  //   - g starts before n and is not associated to the node before n
   130  //     via the previous rules
   131  //
   132  // NewCommentMap tries to associate a comment group to the "largest"
   133  // node possible: For instance, if the comment is a line comment
   134  // trailing an assignment, the comment is associated with the entire
   135  // assignment rather than just the last operand in the assignment.
   136  func NewCommentMap(fset *token.FileSet, node Node, comments []*CommentGroup) CommentMap {
   137  	if len(comments) == 0 {
   138  		return nil // no comments to map
   139  	}
   140  
   141  	cmap := make(CommentMap)
   142  
   143  	// set up comment reader r
   144  	tmp := make([]*CommentGroup, len(comments))
   145  	copy(tmp, comments) // don't change incoming comments
   146  	sortComments(tmp)
   147  	r := commentListReader{fset: fset, list: tmp} // !r.eol() because len(comments) > 0
   148  	r.next()
   149  
   150  	// create node list in lexical order
   151  	nodes := nodeList(node)
   152  	nodes = append(nodes, nil) // append sentinel
   153  
   154  	// set up iteration variables
   155  	var (
   156  		p     Node           // previous node
   157  		pend  token.Position // end of p
   158  		pg    Node           // previous node group (enclosing nodes of "importance")
   159  		pgend token.Position // end of pg
   160  		stack nodeStack      // stack of node groups
   161  	)
   162  
   163  	for _, q := range nodes {
   164  		var qpos token.Position
   165  		if q != nil {
   166  			qpos = fset.Position(q.Pos()) // current node position
   167  		} else {
   168  			// set fake sentinel position to infinity so that
   169  			// all comments get processed before the sentinel
   170  			const infinity = 1 << 30
   171  			qpos.Offset = infinity
   172  			qpos.Line = infinity
   173  		}
   174  
   175  		// process comments before current node
   176  		for r.end.Offset <= qpos.Offset {
   177  			// determine recent node group
   178  			if top := stack.pop(r.comment.Pos()); top != nil {
   179  				pg = top
   180  				pgend = fset.Position(pg.End())
   181  			}
   182  			// Try to associate a comment first with a node group
   183  			// (i.e., a node of "importance" such as a declaration);
   184  			// if that fails, try to associate it with the most recent
   185  			// node.
   186  			// TODO(gri) try to simplify the logic below
   187  			var assoc Node
   188  			switch {
   189  			case pg != nil &&
   190  				(pgend.Line == r.pos.Line ||
   191  					pgend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line):
   192  				// 1) comment starts on same line as previous node group ends, or
   193  				// 2) comment starts on the line immediately after the
   194  				//    previous node group and there is an empty line before
   195  				//    the current node
   196  				// => associate comment with previous node group
   197  				assoc = pg
   198  			case p != nil &&
   199  				(pend.Line == r.pos.Line ||
   200  					pend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line ||
   201  					q == nil):
   202  				// same rules apply as above for p rather than pg,
   203  				// but also associate with p if we are at the end (q == nil)
   204  				assoc = p
   205  			default:
   206  				// otherwise, associate comment with current node
   207  				if q == nil {
   208  					// we can only reach here if there was no p
   209  					// which would imply that there were no nodes
   210  					panic("internal error: no comments should be associated with sentinel")
   211  				}
   212  				assoc = q
   213  			}
   214  			cmap.addComment(assoc, r.comment)
   215  			if r.eol() {
   216  				return cmap
   217  			}
   218  			r.next()
   219  		}
   220  
   221  		// update previous node
   222  		p = q
   223  		pend = fset.Position(p.End())
   224  
   225  		// update previous node group if we see an "important" node
   226  		switch q.(type) {
   227  		case *File, *Field, Decl, Spec, Stmt:
   228  			stack.push(q)
   229  		}
   230  	}
   231  
   232  	return cmap
   233  }
   234  
   235  // Update replaces an old node in the comment map with the new node
   236  // and returns the new node. Comments that were associated with the
   237  // old node are associated with the new node.
   238  func (cmap CommentMap) Update(old, new Node) Node {
   239  	if list := cmap[old]; len(list) > 0 {
   240  		delete(cmap, old)
   241  		cmap[new] = append(cmap[new], list...)
   242  	}
   243  	return new
   244  }
   245  
   246  // Filter returns a new comment map consisting of only those
   247  // entries of cmap for which a corresponding node exists in
   248  // the AST specified by node.
   249  func (cmap CommentMap) Filter(node Node) CommentMap {
   250  	umap := make(CommentMap)
   251  	Inspect(node, func(n Node) bool {
   252  		if g := cmap[n]; len(g) > 0 {
   253  			umap[n] = g
   254  		}
   255  		return true
   256  	})
   257  	return umap
   258  }
   259  
   260  // Comments returns the list of comment groups in the comment map.
   261  // The result is sorted in source order.
   262  func (cmap CommentMap) Comments() []*CommentGroup {
   263  	list := make([]*CommentGroup, 0, len(cmap))
   264  	for _, e := range cmap {
   265  		list = append(list, e...)
   266  	}
   267  	sortComments(list)
   268  	return list
   269  }
   270  
   271  func summary(list []*CommentGroup) string {
   272  	const maxLen = 40
   273  	var buf bytes.Buffer
   274  
   275  	// collect comments text
   276  loop:
   277  	for _, group := range list {
   278  		// Note: CommentGroup.Text() does too much work for what we
   279  		//       need and would only replace this innermost loop.
   280  		//       Just do it explicitly.
   281  		for _, comment := range group.List {
   282  			if buf.Len() >= maxLen {
   283  				break loop
   284  			}
   285  			buf.WriteString(comment.Text)
   286  		}
   287  	}
   288  
   289  	// truncate if too long
   290  	if buf.Len() > maxLen {
   291  		buf.Truncate(maxLen - 3)
   292  		buf.WriteString("...")
   293  	}
   294  
   295  	// replace any invisibles with blanks
   296  	bytes := buf.Bytes()
   297  	for i, b := range bytes {
   298  		switch b {
   299  		case '\t', '\n', '\r':
   300  			bytes[i] = ' '
   301  		}
   302  	}
   303  
   304  	return string(bytes)
   305  }
   306  
   307  func (cmap CommentMap) String() string {
   308  	// print map entries in sorted order
   309  	var nodes []Node
   310  	for node := range cmap {
   311  		nodes = append(nodes, node)
   312  	}
   313  	slices.SortFunc(nodes, func(a, b Node) int {
   314  		r := cmp.Compare(a.Pos(), b.Pos())
   315  		if r != 0 {
   316  			return r
   317  		}
   318  		return cmp.Compare(a.End(), b.End())
   319  	})
   320  
   321  	var buf strings.Builder
   322  	fmt.Fprintln(&buf, "CommentMap {")
   323  	for _, node := range nodes {
   324  		comment := cmap[node]
   325  		// print name of identifiers; print node type for other nodes
   326  		var s string
   327  		if ident, ok := node.(*Ident); ok {
   328  			s = ident.Name
   329  		} else {
   330  			s = fmt.Sprintf("%T", node)
   331  		}
   332  		fmt.Fprintf(&buf, "\t%p  %20s:  %s\n", node, s, summary(comment))
   333  	}
   334  	fmt.Fprintln(&buf, "}")
   335  	return buf.String()
   336  }
   337
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