Improved error message for version restrictions

src/cli.cr

@@ -166,6 +166,6 @@ rescue ex : Shards::ParseError
   ex.to_s(STDERR)
   exit 1
 rescue ex : Shards::Error
-  Shards::Log.error { ex.message }
+  Shards::Log.error { ex.message.to_s }
   exit 1
 end

src/commands/command.cr

@@ -1,6 +1,7 @@
 require "../lock"
 require "../spec"
 require "../override"
+require "levenshtein"
 
 module Shards
   abstract class Command
@@ -73,8 +74,49 @@ module Shards
       Shards::Lock.write(packages, override_path, LOCK_FILENAME)
     end
 
-    def handle_resolver_errors(&)
+    private def log_available_tags(conflicts)
+      String.build do |str|
+        shard_source_dependencys = conflicts.flat_map { |k, v| v.requirements.flat_map { |source, deps| deps.map { |dep| {k, source, dep} } } }
+        if shard_source_dependencys.size > 1
+          str << "Unable to satisfy the following requirements:\n\n"
+          shard_source_dependencys.each do |shard, source, dependency|
+            str << "- `#{shard} (#{dependency.requirement})` required by `#{source}`\n"
+          end
+        else
+          str << "Unable to satisfy the following requirement:\n\n"
+          shard_source_dependencys.each do |shard, source, dependency|
+            resolver = dependency.resolver
+            tags = resolver.available_tags.reverse!.first(5)
+            releases = resolver.available_releases.map(&.to_s).reverse
+            req = dependency.requirement
+
+            str << "- `#{shard} (#{req})` required by `#{source}`: "
+            if releases.empty?
+              str << "It doesn't have any release. "
+              if tags.empty?
+                str << "And it doesn't have any tags either."
+              else
+                str << "These are the latest tags: #{tags.join(", ")}."
+              end
+            elsif req.is_a?(Version) || (req.is_a?(VersionReq) && req.patterns.size == 1 && req.patterns[0] !~ /^(<|>|=)/)
+              req = req.to_s
+              found = Levenshtein.find(req, releases, 6) || "none"
+              info = "These are the latest tags: #{tags.join(", ")}."
+              str << "The closest available release to #{req} is: #{found}. #{info}"
+            else
+              str << "The last available releases are #{releases.first(5).join(", ")}."
+            end
+            str << "\n"
+          end
+        end
+      end
+    end
+
+    def handle_resolver_errors(solver, &)
       yield
+    rescue e : Molinillo::VersionConflict(Shards::Dependency, Shards::Spec)
+      Log.error { log_available_tags(e.conflicts) }
+      raise Shards::Error.new("Failed to resolve dependencies")
     rescue e : Molinillo::ResolverError
       Log.error { e.message }
       raise Shards::Error.new("Failed to resolve dependencies")

src/commands/install.cr

@@ -21,7 +21,7 @@ module Shards
 
         solver.prepare(development: Shards.with_development?)
 
-        packages = handle_resolver_errors { solver.solve }
+        packages = handle_resolver_errors(solver) { solver.solve }
 
         if Shards.frozen?
           validate(packages)

src/commands/lock.cr

@@ -26,7 +26,7 @@ module Shards
 
         solver.prepare(development: Shards.with_development?)
 
-        packages = handle_resolver_errors { solver.solve }
+        packages = handle_resolver_errors(solver) { solver.solve }
         return if packages.empty?
 
         if print

src/commands/outdated.cr

@@ -18,7 +18,7 @@ module Shards
         solver = MolinilloSolver.new(spec, override, prereleases: @prereleases)
         solver.prepare(development: Shards.with_development?)
 
-        packages = handle_resolver_errors { solver.solve }
+        packages = handle_resolver_errors(solver) { solver.solve }
         packages.each { |package| analyze(package) }
 
         if @up_to_date

src/commands/update.cr

@@ -19,7 +19,7 @@ module Shards
 
         solver.prepare(development: Shards.with_development?)
 
-        packages = handle_resolver_errors { solver.solve }
+        packages = handle_resolver_errors(solver) { solver.solve }
         install(packages)
 
         if generate_lockfile?(packages)

src/resolvers/crystal.cr

@@ -10,6 +10,10 @@ module Shards
       [Version.new Shards.crystal_version]
     end
 
+    def available_tags : Array(String)
+      [Shards.crystal_version]
+    end
+
     def read_spec(version : Version) : String?
       nil
     end

src/resolvers/fossil.cr

@@ -212,10 +212,13 @@ module Shards
       end
     end
 
-    protected def versions_from_tags
+    def available_tags : Array(String)
       capture("fossil tag list -R #{Process.quote(local_fossil_file)}")
-        .split('\n')
-        .compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
+        .lines.reject!(&.empty?)
+    end
+
+    protected def versions_from_tags
+      available_tags.compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
     end
 
     def install_sources(version : Version, install_path : String)

src/resolvers/git.cr

@@ -203,10 +203,13 @@ module Shards
       end
     end
 
-    protected def versions_from_tags
+    def available_tags : Array(String)
       capture("git tag --list #{GitResolver.git_column_never}")
-        .split('\n')
-        .compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
+        .lines.reject!(&.empty?)
+    end
+
+    protected def versions_from_tags
+      available_tags.compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
     end
 
     def install_sources(version : Version, install_path : String)

src/resolvers/hg.cr

@@ -186,6 +186,14 @@ module Shards
     rescue Error
     end
 
+    def available_tags : Array(String)
+      tags = capture("hg tags --template #{Process.quote("{tag}\n")}")
+        .lines
+        .sort!
+
+      tags.reject!(&.empty?)
+    end
+
     def available_releases : Array(Version)
       update_local_cache
       versions_from_tags
@@ -221,10 +229,11 @@ module Shards
     end
 
     protected def versions_from_tags
-      capture("hg tags --template #{Process.quote("{tag}\n")}")
+      tags = capture("hg tags --template #{Process.quote("{tag}\n")}")
         .lines
         .sort!
-        .compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
+
+      tags.compact_map { |tag| Version.new($1) if tag =~ VERSION_TAG }
     end
 
     def install_sources(version : Version, install_path : String)

src/resolvers/path.cr

@@ -24,6 +24,10 @@ module Shards
       [spec(nil).version]
     end
 
+    def available_tags : Array(String)
+      [spec(nil).version.to_s]
+    end
+
     def local_path
       source
     end

src/resolvers/resolver.cr

@@ -54,6 +54,8 @@ module Shards
       end
     end
 
+    abstract def available_tags : Array(String)
+
     abstract def available_releases : Array(Version)
 
     def latest_version_for_ref(ref : Ref?) : Version