json-parser: basic support for ShellCheck's JSON output

... which is produced by `shellcheck --format=json ...`

Fixes: #75

src/json-parser.cc

@@ -109,6 +109,15 @@ class GccTreeDecoder: public AbstractTreeDecoder {
         const GccPostProcessor postProc;
 };
 
+/// tree decoder of the JSON format produced by ShellCheck
+class ShellCheckTreeDecoder: public AbstractTreeDecoder {
+    public:
+        bool readNode(Defect *def, pt::ptree::const_iterator defIter) override;
+
+    private:
+        const GccPostProcessor postProc;
+};
+
 struct JsonParser::Private {
     InStream                       &input;
     AbstractTreeDecoder            *decoder = nullptr;
@@ -168,7 +177,11 @@ JsonParser::JsonParser(InStream &input):
         else if (findChildOf(&node, d->root, "runs"))
             // SARIF format
             d->decoder = new SarifTreeDecoder;
+        else if (findChildOf(&node, d->root, "comments"))
+            // ShellCheck JSON format
+            d->decoder = new ShellCheckTreeDecoder;
         else if (first.not_found() != first.find("kind"))
+            // GCC JSON format
             d->decoder = new GccTreeDecoder;
         else
             throw pt::ptree_error("unknown JSON format");
@@ -781,3 +794,49 @@ bool GccTreeDecoder::readNode(Defect *def, pt::ptree::const_iterator defIter)
 
     return true;
 }
+
+static bool scReadEvent(DefEvent *pEvt, const pt::ptree &evtNode)
+{
+    using std::string;
+
+    // read level (error, warning, note)
+    string &evtName = pEvt->event;
+    evtName = valueOf<string>(evtNode, "level", "");
+    if (evtName.empty())
+        return false;
+
+    // read location
+    pEvt->fileName = valueOf<string>(evtNode, "file", "<unknown>");
+    pEvt->line     = valueOf<int>   (evtNode, "line", 0);
+    pEvt->column   = valueOf<int>   (evtNode, "byte-column", 0);
+
+    // read message
+    pEvt->msg = valueOf<string>(evtNode, "message", "<unknown>");
+
+    // append [SC...] if available
+    const string code = valueOf<string>(evtNode, "code", "");
+    if (!code.empty())
+        pEvt->msg += " [SC" + code + "]";
+
+    return true;
+}
+
+bool ShellCheckTreeDecoder::readNode(
+        Defect                     *def,
+        pt::ptree::const_iterator   defIter)
+{
+    *def = Defect("SHELLCHECK_WARNING");
+    const pt::ptree &defNode = defIter->second;
+
+    // read key event
+    def->events.push_back(DefEvent());
+    if (!scReadEvent(&def->events.back(), defNode))
+        return false;
+
+    // TODO: go through fix/replacements nodes
+
+    // apply post-processing rules
+    this->postProc.apply(def);
+
+    return true;
+}

tests/csgrep/98-json-parser-shellcheck-args.txt

@@ -0,0 +1 @@
+--mode=json