Output the correct location when a statement can not be parsed. (#499)

* Output the correct location when a statement can not be parsed.

Currently the start of the current compound statement is provided as a
hint.

* Tweak error message wording

Signed-off-by: Herb Sutter <[email protected]>

---------

Signed-off-by: Herb Sutter <[email protected]>
Co-authored-by: Herb Sutter <[email protected]>

Author: MaxSagebaum

regression-tests/pure2-statement-parse-error.cpp2

@@ -0,0 +1,5 @@
+func: () = {
+    a : int = 5;
+    int b = 4;
+    c: int = 3;
+}

regression-tests/test-results/pure2-statement-parse-error.cpp2.output

@@ -0,0 +1,3 @@
+pure2-statement-parse-error.cpp2...
+pure2-statement-parse-error.cpp2(3,9): error: Could not parse statement (at 'b')
+

source/parse.h

@@ -3920,6 +3920,10 @@ class parser
         error( msg.c_str(), include_curr_token, err_pos, fallback );
     }
 
+    bool has_error() {
+        return !errors.empty();
+    }
+
 
     //-----------------------------------------------------------------------
     //  Token navigation: Only these functions should access this->token_
@@ -5772,6 +5776,11 @@ class parser
             //  contained statement() may have parameters
             auto s = statement(true, source_position{}, true, n.get());
             if (!s) {
+
+                // Only add error when no specific one already exist
+                if(!has_error()) {
+                    error("Invalid statement encountered inside a compound-statement", true);
+                }
                 pos = start_pos;    // backtrack
                 return {};
             }