Add wiki links to output, and a -W controlling it. (Fixes #920)

CHANGELOG.md

 ## ???
 ### Added
 - Command line option --severity/-S for filtering by minimum severity
+- Command line option --wiki-link-count/-W for showing wiki links
 - SC2236/SC2237: Suggest -n/-z instead of ! -z/-n
 - SC2238: Warn when redirecting to a known command name, e.g. ls > rm
 ### Changed

shellcheck.1.md

@@ -71,6 +71,11 @@ not warn at all, as `ksh` supports decimals in arithmetic contexts.
 
 :   Print version information and exit.
 
+**-W** *NUM*,\ **--wiki-link-count=NUM**
+
+:   For TTY output, show *NUM* wiki links to more information about mentioned
+    warnings. Set to 0 to disable them entirely.
+
 **-x**,\ **--external-sources**
 
 :   Follow 'source' statements even when the file is not specified as input.

shellcheck.hs

@@ -100,6 +100,9 @@ options = [
         "Minimum severity of errors to consider (error, warning, info, style)",
     Option "V" ["version"]
         (NoArg $ Flag "version" "true") "Print version information",
+    Option "W" ["wiki-link-count"]
+        (ReqArg (Flag "wiki-link-count") "NUM")
+        "The number of wiki links to show, when applicable.",
     Option "x" ["external-sources"]
         (NoArg $ Flag "externals" "true") "Allow 'source' outside of FILES"
     ]
@@ -296,6 +299,14 @@ parseOption flag options =
                 }
             }
 
+        Flag "wiki-link-count" countString -> do
+            count <- parseNum countString
+            return options {
+                formatterOptions = (formatterOptions options) {
+                    foWikiLinkCount = count
+                }
+            }
+
         _ -> return options
   where
     die s = do
@@ -304,7 +315,7 @@ parseOption flag options =
     parseNum ('S':'C':str) = parseNum str
     parseNum num = do
         unless (all isDigit num) $ do
-            printErr $ "Bad exclusion: " ++ num
+            printErr $ "Invalid number: " ++ num
             throwError SyntaxFailure
         return (Prelude.read num :: Integer)
 

src/ShellCheck/Formatter/TTY.hs

@@ -22,18 +22,27 @@ module ShellCheck.Formatter.TTY (format) where
 import ShellCheck.Interface
 import ShellCheck.Formatter.Format
 
+import Control.Monad
+import Data.IORef
 import Data.List
 import GHC.Exts
-import System.Info
 import System.IO
+import System.Info
+
+wikiLink = "https://www.shellcheck.net/wiki/"
+
+-- An arbitrary Ord thing to order warnings
+type Ranking = (Char, Severity, Integer)
 
 format :: FormatterOptions -> IO Formatter
-format options = return Formatter {
-    header = return (),
-    footer = return (),
-    onFailure = outputError options,
-    onResult = outputResult options
-}
+format options = do
+    topErrorRef <- newIORef []
+    return Formatter {
+        header = return (),
+        footer = outputWiki topErrorRef,
+        onFailure = outputError options,
+        onResult = outputResult options topErrorRef
+    }
 
 colorForLevel level =
     case level of
@@ -45,13 +54,60 @@ colorForLevel level =
         "source"  -> 0 -- none
         _ -> 0         -- none
 
+rankError :: PositionedComment -> Ranking
+rankError err = (ranking, cSeverity $ pcComment err, cCode $ pcComment err)
+  where
+    ranking =
+        if cCode (pcComment err) `elem` uninteresting
+        then 'Z'
+        else 'A'
+
+    -- A list of the most generic, least directly helpful
+    -- error codes to downrank.
+    uninteresting = [
+        1009, -- Mentioned parser error was..
+        1019, -- Expected this to be an argument
+        1036, -- ( is invalid here
+        1047, -- Expected 'fi'
+        1062, -- Expected 'done'
+        1070, -- Parsing stopped here (generic)
+        1072, -- Missing/unexpected ..
+        1073, -- Couldn't parse this ..
+        1088, -- Parsing stopped here (paren)
+        1089  -- Parsing stopped here (keyword)
+        ]
+
+appendComments errRef comments max = do
+    previous <- readIORef errRef
+    let current = map (\x -> (rankError x, cCode $ pcComment x, cMessage $ pcComment x)) comments
+    writeIORef errRef . take max . nubBy equal . sort $ previous ++ current
+  where
+    fst3 (x,_,_) = x
+    equal x y = fst3 x == fst3 y
+
+outputWiki :: IORef [(Ranking, Integer, String)] -> IO ()
+outputWiki errRef = do
+    issues <- readIORef errRef
+    unless (null issues) $ do
+        putStrLn "For more information:"
+        mapM_ showErr issues
+  where
+    showErr (_, code, msg) =
+        putStrLn $ "  " ++ wikiLink ++ "SC" ++ show code ++ " -- " ++ shorten msg
+    limit = 40
+    shorten msg =
+        if length msg < limit
+        then msg
+        else (take (limit-3) msg) ++ "..."
+
 outputError options file error = do
     color <- getColorFunc $ foColorOption options
     hPutStrLn stderr $ color "error" $ file ++ ": " ++ error
 
-outputResult options result sys = do
+outputResult options ref result sys = do
     color <- getColorFunc $ foColorOption options
     let comments = crComments result
+    appendComments ref comments (fromIntegral $ foWikiLinkCount options)
     let fileGroups = groupWith sourceFile comments
     mapM_ (outputForFile color sys) fileGroups
 
@@ -87,7 +143,7 @@ cuteIndent comment =
         in
             if sameLine && delta > 2 && delta < 32 then arrow delta else "^--"
 
-code code = "SC" ++ show code
+code num = "SC" ++ show num
 
 getColorFunc colorOption = do
     term <- hIsTerminalDevice stdout

src/ShellCheck/Interface.hs

@@ -26,7 +26,7 @@ module ShellCheck.Interface
     , ParseResult(prComments, prTokenPositions, prRoot)
     , AnalysisSpec(asScript, asShellType, asExecutionMode, asCheckSourced)
     , AnalysisResult(arComments)
-    , FormatterOptions(foColorOption)
+    , FormatterOptions(foColorOption, foWikiLinkCount)
     , Shell(Ksh, Sh, Bash, Dash)
     , ExecutionMode(Executed, Sourced)
     , ErrorMessage
@@ -145,12 +145,14 @@ newAnalysisResult = AnalysisResult {
 }
 
 -- Formatter options
-newtype FormatterOptions = FormatterOptions {
-    foColorOption :: ColorOption
+data FormatterOptions = FormatterOptions {
+    foColorOption :: ColorOption,
+    foWikiLinkCount :: Integer
 }
 
 newFormatterOptions = FormatterOptions {
-    foColorOption = ColorAuto
+    foColorOption = ColorAuto,
+    foWikiLinkCount = 3
 }