Added clearer error reporting when skipping pre-releases

piptools/exceptions.py

@@ -3,22 +3,44 @@ class PipToolsError(Exception):
 
 
 class NoCandidateFound(PipToolsError):
-    def __init__(self, ireq, candidates_tried, index_urls):
+    def __init__(self, ireq, candidates_tried, finder):
         self.ireq = ireq
         self.candidates_tried = candidates_tried
-        self.index_urls = index_urls
+        self.finder = finder
 
     def __str__(self):
-        sorted_versions = sorted(c.version for c in self.candidates_tried)
+        versions = []
+        pre_versions = []
+
+        for candidate in sorted(self.candidates_tried):
+            version = str(candidate.version)
+            if candidate.version.is_prerelease:
+                pre_versions.append(version)
+            else:
+                versions.append(version)
+
         lines = [
             'Could not find a version that matches {}'.format(self.ireq),
-            'Tried: {}'.format(', '.join(str(version) for version in sorted_versions) or '(no version found at all)')
         ]
-        if sorted_versions:
+
+        if versions:
+            lines.append('Tried: {}'.format(', '.join(versions)))
+
+        if pre_versions:
+            if self.finder.allow_all_prereleases:
+                line = 'Tried'
+            else:
+                line = 'Skipped'
+
+            line += ' pre-versions: {}'.format(', '.join(pre_versions))
+            lines.append(line)
+
+        if versions or pre_versions:
             lines.append('There are incompatible versions in the resolved dependencies.')
         else:
+            lines.append('No versions found')
             lines.append('{} {} reachable?'.format(
-                'Were' if len(self.index_urls) > 1 else 'Was', ' or '.join(self.index_urls))
+                'Were' if len(self.finder.index_urls) > 1 else 'Was', ' or '.join(self.finder.index_urls))
             )
         return '\n'.join(lines)
 

piptools/repositories/pypi.py

@@ -104,7 +104,7 @@ def find_best_match(self, ireq, prereleases=None):
         # Reuses pip's internal candidate sort key to sort
         matching_candidates = [candidates_by_version[ver] for ver in matching_versions]
         if not matching_candidates:
-            raise NoCandidateFound(ireq, all_candidates, self.finder.index_urls)
+            raise NoCandidateFound(ireq, all_candidates, self.finder)
         best_candidate = max(matching_candidates, key=self.finder._candidate_sort_key)
 
         # Turn the candidate into a pinned InstallRequirement

tests/test_cli.py

@@ -366,3 +366,27 @@ def test_filter_pip_markes():
         assert '--output-file requirements.txt' in out.output
         assert 'six==1.10.0' in out.output
         assert 'unknown_package' not in out.output
+
+
+def test_no_candidates():
+    runner = CliRunner()
+    with runner.isolated_filesystem():
+        with open('requirements', 'w') as req_in:
+            req_in.write('six>1.0b0,<1.0b0')
+
+        out = runner.invoke(cli, ['-n', 'requirements'])
+
+        assert out.exit_code == 2
+        assert 'Skipped pre-versions:' in out.output
+
+
+def test_no_candidates_pre():
+    runner = CliRunner()
+    with runner.isolated_filesystem():
+        with open('requirements', 'w') as req_in:
+            req_in.write('six>1.0b0,<1.0b0')
+
+        out = runner.invoke(cli, ['-n', 'requirements', '--pre'])
+
+        assert out.exit_code == 2
+        assert 'Tried pre-versions:' in out.output

tox.ini

@@ -3,6 +3,7 @@ envlist =
     py{27,34,35,36,py}
     flake8
     readme
+skip_missing_interpreters = True
 
 [testenv]
 deps =