give better error messages for undefined modules and functions

src/parse/value/parse.rs

@@ -224,7 +224,7 @@ impl<'a> Parser<'a> {
                 let value = self
                     .modules
                     .get(module)
-                    .ok_or(("todo: module dne", module_span))?
+                    .ok_or((format!("There is no module with the namespace \"{}\".", module), module_span))?
                     .get_var(var)?;
                 HigherIntermediateValue::Literal(value.clone())
             } else {
@@ -235,9 +235,9 @@ impl<'a> Parser<'a> {
                 let function = self
                     .modules
                     .get(module)
-                    .ok_or(("todo: module dne", module_span))?
+                    .ok_or((format!("There is no module with the namespace \"{}\".", module), module_span))?
                     .get_fn(fn_name.node)
-                    .ok_or(("todo: fn dne", fn_name.span))?;
+                    .ok_or(("Undefined function.", fn_name.span))?;
 
                 if !matches!(self.toks.next(), Some(Token { kind: '(', .. })) {
                     todo!()

tests/use.rs

@@ -25,6 +25,21 @@ error!(
     "@use \"sass:math\" a math;",
     "Error: expected \";\"."
 );
+error!(
+    unknown_module_get_variable,
+    "a { color: foo.$bar; }",
+    "Error: There is no module with the namespace \"foo\"."
+);
+error!(
+    unknown_module_get_function,
+    "a { color: foo.bar(); }",
+    "Error: There is no module with the namespace \"foo\"."
+);
+error!(
+    unknown_function,
+    "@use \"sass:math\";\na { color: math.bar(); }",
+    "Error: Undefined function."
+);
 test!(
     use_as,
     "@use \"sass:math\" as foo;