Importing the same item multiple times should be a compile error

sway-core/src/error.rs

@@ -797,6 +797,8 @@ pub enum CompileError {
     },
     #[error("The name \"{name}\" shadows another symbol with the same name.")]
     ShadowsOtherSymbol { name: String, span: Span },
+    #[error("The name \"{name}\" imported through `*` shadows another symbol with the same name.")]
+    StarImportShadowsOtherSymbol { name: String, span: Span },
     #[error(
         "Match expression arm has mismatched types.\n\
          expected: {expected}\n\
@@ -1004,6 +1006,7 @@ impl CompileError {
             ArrayOutOfBounds { span, .. } => span,
             TupleOutOfBounds { span, .. } => span,
             ShadowsOtherSymbol { span, .. } => span,
+            StarImportShadowsOtherSymbol { span, .. } => span,
             MatchWrongType { span, .. } => span,
             NotAnEnum { span, .. } => span,
             PatternMatchingAlgorithmFailure(_, span) => span,

sway-core/src/semantic_analysis/namespace/arena.rs

@@ -304,10 +304,16 @@ impl NamespaceWrapper for NamespaceRef {
             namespace,
         );
         write_module(
-            move |m| {
+            |m| {
                 m.implemented_traits
                     .extend(&mut implemented_traits.into_iter());
                 for symbol in symbols {
+                    if m.use_synonyms.contains_key(&symbol) {
+                        errors.push(CompileError::StarImportShadowsOtherSymbol {
+                            name: symbol.as_str().to_string(),
+                            span: symbol.span().clone(),
+                        });
+                    }
                     m.use_synonyms.insert(symbol, path.clone());
                 }
             },
@@ -487,11 +493,23 @@ impl NamespaceWrapper for NamespaceRef {
                         // no matter what, import it this way though.
                         match alias.clone() {
                             Some(alias) => {
+                                if m.use_synonyms.contains_key(&alias) {
+                                    errors.push(CompileError::ShadowsOtherSymbol {
+                                        name: alias.as_str().to_string(),
+                                        span: alias.span().clone(),
+                                    });
+                                }
                                 m.use_synonyms.insert(alias.clone(), path.clone());
                                 m.use_aliases
                                     .insert(alias.as_str().to_string(), item.clone());
                             }
                             None => {
+                                if m.use_synonyms.contains_key(item) {
+                                    errors.push(CompileError::ShadowsOtherSymbol {
+                                        name: item.as_str().to_string(),
+                                        span: item.span().clone(),
+                                    });
+                                }
                                 m.use_synonyms.insert(item.clone(), path.clone());
                             }
                         };

test/src/e2e_vm_tests/mod.rs

@@ -121,6 +121,7 @@ pub fn run(filter_regex: Option<regex::Regex>) {
         "contract_pure_calls_impure",
         "literal_too_large_for_type",
         "item_used_without_import",
+        "shadow_import",
     ];
     number_of_tests_run += negative_project_names.iter().fold(0, |acc, name| {
         if filter(name) {

test/src/e2e_vm_tests/test_programs/multi_item_import/src/main.sw

@@ -2,7 +2,7 @@ script;
 
 dep bar;
 
-use ::bar::{Bar1 as MyBar1, Bar2, double_bar::{DoubleBar1 as MyDoubleBar1, DoubleBar2, *}};
+use ::bar::{Bar1 as MyBar1, Bar2, double_bar::{DoubleBar1 as MyDoubleBar1, DoubleBar2, DoubleBar3}};
 
 fn main() -> bool {
     let bar1 = MyBar1 {

test/src/e2e_vm_tests/test_programs/shadow_import/Forc.toml

@@ -0,0 +1,5 @@
+[project]
+author = "Fuel Labs <contact@fuel.sh>"
+license = "Apache-2.0"
+name = "shadow_import"
+entry = "main.sw"

test/src/e2e_vm_tests/test_programs/shadow_import/json_abi_oracle.json

@@ -0,0 +1 @@
+[]

test/src/e2e_vm_tests/test_programs/shadow_import/src/bar.sw

@@ -0,0 +1,13 @@
+library bar;
+
+pub struct Bar1 {
+    a: u32,
+}
+
+pub struct Bar2 {
+    b: u32,
+}
+
+pub struct Bar3 {
+    c: u32,
+}

test/src/e2e_vm_tests/test_programs/shadow_import/src/main.sw

@@ -0,0 +1,19 @@
+script;
+
+dep bar;
+
+// This is okay
+use ::bar::{Bar1, Bar1 as Foo};
+
+// This is not okay because symbol `Foo` is already reserved
+use ::bar::Bar2 as Foo;
+
+// This is not okay 
+use ::bar::{Bar2, Bar2};
+
+// This not okay now because Bar1 and Bar2 have already been imported
+use ::bar::*;
+
+fn main() -> bool {
+    false
+}