[DRAFT] Change table load to retain original header row, for improved errors

src/arr/trove/csv.arr

@@ -60,7 +60,7 @@ fun to-content<A>(csv :: RawArray<RawArray<String>>)
 end
 
 
-fun csv-table-opt(csv :: RawArray<RawArray<String>>, opts :: CSVOptions):
+fun csv-table-opt(csv :: RawArray<RawArray<String>>, orig-headers :: O.Option<RawArray<String>>, opts :: CSVOptions):
   shadow opts = builtins.record-concat(default-options, opts)
   {
     load: lam(headers, sanis) block:
@@ -76,20 +76,30 @@ fun csv-table-opt(csv :: RawArray<RawArray<String>>, opts :: CSVOptions):
           result
         end
 
-        { headers; contents }
+        { headers; orig-headers; contents }
       end
   }
 end
 
 fun csv-table(csv :: RawArray<RawArray<String>>) -> { load :: Function }:
-  csv-table-opt(csv, default-options)
+  csv-table-opt(csv, O.none, default-options)
 end
 
 fun csv-table-str(csv :: String, opts):
   shadow opts = builtins.record-concat(default-options, opts)
   skip-rows = if opts.header-row: 1 else: 0 end
-  rows = csv-lib.parse-string(csv, { skipRows: skip-rows })
-  csv-table-opt(rows, opts)
+  rows = csv-lib.parse-string(csv, {})
+  contents = if opts.header-row:
+    raw-array-from-list(raw-array-to-list(rows).drop(1))
+  else:
+    rows
+  end
+  headers = if opts.header-row and (raw-array-length(rows) > 0):
+    O.some(raw-array-get(rows, 0))
+  else:
+    O.none
+  end
+  csv-table-opt(contents, headers, opts)
 end
 
 fun csv-table-file(path :: String, opts):

src/arr/trove/error.arr

@@ -18,6 +18,9 @@ end
 fun horz-list-values(vals):
   [ED.para: ED.h-sequence(vals.map(lam(val): ED.embed(val) end), ",") ]
 end
+fun horz-list-str-ids(vals):
+  [ED.para: ED.h-sequence(vals.map(lam(val): ED.text(val) end), ",") ]
+end
 
 fun ed-simple-intro(name, loc):
   ed-simple-intro-a-an(name, loc, "a")
@@ -1925,6 +1928,39 @@ data RuntimeError:
           vert-list-values(self.fun-app-args)])
     end
 
+    | header-row-mismatch(expected-headers, orig-headers, provided-row) with:
+    method render-fancy-reason(self, maybe-stack-loc, src-available, maybe-ast):
+      cases(O.Option) maybe-stack-loc(0, true):
+        | some(l) =>
+          [ED.error:
+            ed-intro("table construction", l, -1, true),
+            [ED.para: ED.text("The table could not be constructed because the number of expected headers didn't match the number found in the data.")],
+            [ED.para: ED.text("Expected to have " + num-to-string(raw-array-length(self.expected-headers)) + " columns:")],
+            horz-list-str-ids(raw-array-to-list(self.expected-headers)),
+            cases(O.Option) self.orig-headers:
+              | some(oh) =>
+                [ED.para: [ED.para: ED.text("Instead, found header with " + num-to-string(raw-array-length(oh)) + " columns:"),
+                                    horz-list-str-ids(raw-array-to-list(oh))],
+                          [ED.para: ED.text("And data with " + num-to-string(raw-array-length(self.provided-row)) + " columns:"),
+                                    horz-list-values(raw-array-to-list(self.provided-row))]]
+              | none =>
+                [ED.para: ED.text("But found data with " + num-to-string(raw-array-length(self.provided-row)) + " columns:"),
+                                   horz-list-values(raw-array-to-list(self.provided-row))]
+            end,
+            ]
+        | none => self.render-reason()
+      end
+    end,
+    method render-reason(self):
+      [ED.error:
+        [ED.para: ED.text("The row could not be constructed because the number of columns didn't match the number of provided values.")],
+        [ED.para: ED.text("Expected " + num-to-string(raw-array-length(self.colnames)) + " columns:")],
+        ED.embed(self.colnames),
+        [ED.para: ED.text("Provided " + num-to-string(raw-array-length(self.provided-vals)) + " values:")],
+        horz-list-values(raw-array-to-list(self.provided-vals))]
+    end
+
+
   | row-length-mismatch(colnames, provided-vals) with:
     method render-fancy-reason(self, maybe-stack-loc, src-available, maybe-ast):
       cases(O.Option) maybe-stack-loc(0, true):

src/js/trove/ffi.js

@@ -371,6 +371,11 @@
       raise(err("arity-mismatch")(funLoc, arity, args, isMethod));
     }
 
+    function throwHeaderRowMismatch(colnames, origHeaders, providedVals) {
+      runtime.checkArray(providedVals);
+      raise(err("header-row-mismatch")(colnames, origHeaders, providedVals));
+    }
+
     function throwRowLengthMismatch(colnames, providedVals) {
       runtime.checkArray(providedVals);
       raise(err("row-length-mismatch")(colnames, providedVals));
@@ -634,6 +639,7 @@
       throwUninitializedIdMkLoc: throwUninitializedIdMkLoc,
       throwArityError: throwArityError,
       throwArityErrorC: throwArityErrorC,
+      throwHeaderRowMismatch: throwHeaderRowMismatch,
       throwRowLengthMismatch: throwRowLengthMismatch,
       throwColLengthMismatch: throwColLengthMismatch,
       throwConstructorArityErrorC: throwConstructorArityErrorC,

src/js/trove/table.js

@@ -165,14 +165,16 @@
 
     function openTable(info) {
       runtime.checkTuple(info);
-      if (info.vals.length != 2) {
-        runtime.ffi.throwMessageException("Expected to find {header; contents} pair, "
+      if (info.vals.length != 3) {
+        runtime.ffi.throwMessageException("Expected to find {header; orig-headers; contents} triple, "
                                           + "but found a tuple of length "
                                           + info.vals.length);
       }
       var headers = info.vals[0];
-      var contents = info.vals[1];
+      var origHeaders = info.vals[1];
+      var contents = info.vals[2];
       runtime.checkArray(headers);
+      // runtime.checkPyretVal(origHeaders); // Can we do better?
       runtime.checkArray(contents);
       var names = [];
       var sanitizers = [];
@@ -194,7 +196,7 @@
           runtime.checkArray(contents[i]);
           if (contents[i].length !== headers.length) {
             if (i === 0) {
-              throw runtime.ffi.throwRowLengthMismatch(names, contents[i]);
+              throw runtime.ffi.throwHeaderRowMismatch(names, origHeaders, contents[i]);
             } else {
               throw runtime.ffi.throwMessageException("Contents must be rectangular");
             }

tests/pyret/tests/test-tables.arr

@@ -90,7 +90,7 @@ check "Basic Table Loading":
       {raw-array-get(titles, 1); sanitizer.sanitizer}]
     contents = [raw-array: [raw-array: DS.c-str(name), DS.c-str("12")],
       [raw-array: DS.c-str("Alice"), DS.c-num(15)]]
-    {headers; contents}
+    {headers; none; contents}
   end
   make-loader = {(x): {load: lam(titles, sanitizer): with-tl(x, titles, sanitizer) end}}
   (load-table: name, age