fix(parser): skip eval_const if parsing errors detected to avoid panic (#15364)

Fixes #14972 #15321 #14706

# Description

Early returns `NotAConstant` if parsing errors exist in the
subexpression.

I'm not sure when the span of a block will be None, and whether there're
better ways to handle none block spans, like a more suitable ShellError
type.

# User-Facing Changes

# Tests + Formatting

+1, but possibly not the easiest way to do it.

# After Submitting

crates/nu-protocol/src/errors/shell_error/mod.rs

@@ -1140,6 +1140,25 @@ This is an internal Nushell error, please file an issue https://github.com/nushe
         span: Span,
     },
 
+    /// TODO: Get rid of this error by moving the check before evaluation
+    ///
+    /// Tried evaluating of a subexpression with parsing error
+    ///
+    /// ## Resolution
+    ///
+    /// Fix the parsing error first.
+    #[error("Found parsing error in expression.")]
+    #[diagnostic(
+        code(nu::shell::parse_error_in_constant),
+        help(
+            "This expression is supposed to be evaluated into a constant, which means error-free."
+        )
+    )]
+    ParseErrorInConstant {
+        #[label("Parsing error detected in expression")]
+        span: Span,
+    },
+
     /// Tried assigning non-constant value to a constant
     ///
     /// ## Resolution

crates/nu-protocol/src/eval_const.rs

@@ -508,6 +508,14 @@ impl Eval for EvalConst {
         block_id: BlockId,
         span: Span,
     ) -> Result<Value, ShellError> {
+        // If parsing errors exist in the subexpression, don't bother to evaluate it.
+        if working_set
+            .parse_errors
+            .iter()
+            .any(|error| span.contains_span(error.span()))
+        {
+            return Err(ShellError::ParseErrorInConstant { span });
+        }
         // TODO: Allow debugging const eval
         let block = working_set.get_block(block_id);
         eval_const_subexpression(working_set, block, PipelineData::empty(), span)?.into_value(span)