Return error message in output of gorge/staticExec. (#18942)

* Return error message in output of gorge/staticExec.

* Document nimLegacyGorgeErrors in changelog.

changelog.md

@@ -89,6 +89,9 @@
 - ORC is now the default memory management strategy. Use
   `--mm:refc` for a transition period.
 
+- The `gorge`/`staticExec` calls will now return a descriptive message in the output
+  if the execution fails for whatever reason. To get back legacy behaviour use `-d:nimLegacyGorgeErrors`.
+
 ## Standard library additions and changes
 
 [//]: # "Changes:"

compiler/gorgeimpl.nim

@@ -49,7 +49,11 @@ proc opGorge*(cmd, input, cache: string, info: TLineInfo; conf: ConfigRef): (str
       if result[1] == 0:
         writeFile(filename, result[0])
     except IOError, OSError:
-      if not readSuccessful: result = ("", -1)
+      if not readSuccessful:
+        when defined(nimLegacyGorgeErrors):
+          result = ("", -1)
+        else:
+          result = ("Error running startProcess: " & getCurrentExceptionMsg(), -1)
   else:
     try:
       var p = startProcess(cmd, workingDir,
@@ -60,4 +64,7 @@ proc opGorge*(cmd, input, cache: string, info: TLineInfo; conf: ConfigRef): (str
       result = p.readOutput
       p.close()
     except IOError, OSError:
-      result = ("", -1)
+      when defined(nimLegacyGorgeErrors):
+        result = ("", -1)
+      else:
+        result = ("Error running startProcess: " & getCurrentExceptionMsg(), -1)