stringutil: emit multiple chunks when pretty printing

stringutil: emit multiple chunks when pretty printing

This avoids concatenating output inside pprintgen() itself. But
the real reason for this is it will make it easier to add
indentation, as we'll need to account for indentation when emitting
each individual object in a collection.

The verbosity of this code compared to the original is a bit
unfortunate. But I suppose this is the price to pay for having
nice things (streaming and indenting).

We could probably abstract the "print a collection" bits into a
generic function to avoid some duplication. But I'm not
overly inclined to do this.

Differential Revision: https://phab.mercurial-scm.org/D4398

--- a/mercurial/utils/stringutil.py	Mon Aug 27 09:02:39 2018 -0700
+++ b/mercurial/utils/stringutil.py	Mon Aug 27 09:05:56 2018 -0700
@@ -60,19 +60,97 @@
         # without coercion.
         yield "bytearray['%s']" % escapestr(bytes(o))
     elif isinstance(o, list):
-        yield '[%s]' % (b', '.join(pprint(a, bprefix=bprefix) for a in o))
+        if not o:
+            yield '[]'
+            return
+
+        yield '['
+
+        for i, a in enumerate(o):
+            for chunk in pprintgen(a, bprefix=bprefix):
+                yield chunk
+
+            if i + 1 < len(o):
+                yield ', '
+
+        yield ']'
     elif isinstance(o, dict):
-        yield '{%s}' % (b', '.join(
-            '%s: %s' % (pprint(k, bprefix=bprefix),
-                        pprint(v, bprefix=bprefix))
-            for k, v in sorted(o.items())))
+        if not o:
+            yield '{}'
+            return
+
+        yield '{'
+
+        for i, (k, v) in enumerate(sorted(o.items())):
+            for chunk in pprintgen(k, bprefix=bprefix):
+                yield chunk
+
+            yield ': '
+
+            for chunk in pprintgen(v, bprefix=bprefix):
+                yield chunk
+
+            if i + 1 < len(o):
+                yield ', '
+
+        yield '}'
     elif isinstance(o, set):
-        yield 'set([%s])' % (b', '.join(
-            pprint(k, bprefix=bprefix) for k in sorted(o)))
+        if not o:
+            yield 'set([])'
+            return
+
+        yield 'set(['
+
+        for i, k in enumerate(sorted(o)):
+            for chunk in pprintgen(k, bprefix=bprefix):
+                yield chunk
+
+            if i + 1 < len(o):
+                yield ', '
+
+        yield '])'
     elif isinstance(o, tuple):
-        yield '(%s)' % (b', '.join(pprint(a, bprefix=bprefix) for a in o))
+        if not o:
+            yield '()'
+            return
+
+        yield '('
+
+        for i, a in enumerate(o):
+            for chunk in pprintgen(a, bprefix=bprefix):
+                yield chunk
+
+            if i + 1 < len(o):
+                yield ', '
+
+        yield ')'
     elif isinstance(o, types.GeneratorType):
-        yield 'gen[%s]' % (b', '.join(pprint(a, bprefix=bprefix) for a in o))
+        # Special case of empty generator.
+        try:
+            nextitem = next(o)
+        except StopIteration:
+            yield 'gen[]'
+            return
+
+        yield 'gen['
+
+        last = False
+
+        while not last:
+            current = nextitem
+
+            try:
+                nextitem = next(o)
+            except StopIteration:
+                last = True
+
+            for chunk in pprintgen(current, bprefix=bprefix):
+                yield chunk
+
+            if not last:
+                yield ', '
+
+        yield ']'
     else:
         yield pycompat.byterepr(o)