unused variables are ok with leading _ (#124)

* test/utils: support RegEx in HeliosTest.fails * unused vars are ok with leading _, IFF actually not used * add pre-push hook * Test current branch if git doesn't provide a list of things to push * test/utils: support RegEx in HeliosTest.fails (after #128) * unused vars are ok with leading _, IFF actually not used --------- Co-authored-by: Randall <[email protected]>
HeliosLang · Sep 30, 2024 · 9a140ae · 9a140ae
1 parent 926c020
commit 9a140ae
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Showing 2 changed files with 44 additions and 3 deletions.
diff --git a/src/scopes/Scope.js b/src/scopes/Scope.js
@@ -218,20 +218,27 @@ export class Scope extends Common {
     }
 
     /**
-     * Asserts that all named values are user.
-     * Throws an error if some are unused.
+     * Asserts that all named values are used.
+     * Throws an error if some are unused, unless they start with "_"
      * Check is only run if we are in strict mode
      * @param {boolean} onlyIfStrict
      */
     assertAllUsed(onlyIfStrict = true) {
         if (!onlyIfStrict || this.isStrict()) {
             for (let [name, entity, used] of this.#values) {
-                if (!(entity instanceof Scope) && !used) {
+                const flaggedUnused = name.value.startsWith("_")
+                if (!used && !(entity instanceof Scope) && !flaggedUnused) {
                     throw CompilerError.reference(
                         name.site,
                         `'${name.toString()}' unused`
                     )
                 }
+                if (flaggedUnused && used) {
+                    throw CompilerError.reference(
+                        name.site,
+                        `_-prefixed variable '${name.toString()}' must be unused`
+                    )
+                }
             }
         }
     }

diff --git a/test/assign.test.js b/test/assign.test.js
@@ -23,6 +23,40 @@ describe("Assign", () => {
             inputs: [int(1)],
             output: int(2)
         },
+        {
+            description: "unused variables throw errors",
+            fails: /ReferenceError.*'b' unused/,
+            main: `testing throws_on_unused
+            func main(a: Int) -> Int {
+                b = 2;
+                a
+            }`,
+            inputs: [int(1)],
+            output: int(1)
+        },
+        {
+            description: "underscore-prefix makes unused variables ok",
+            main: `testing unused_variables_ok_with_underscore
+            func main(a: Int) -> Int {
+                _ = 1;
+                _also_unused = 2;
+                a + 1
+            }`,
+            inputs: [int(1)],
+            output: int(2)
+        },
+        {
+            description: "used variables must not be underscore-prefixed",
+            fails: /_-prefixed variable '_thing' must be unused/,
+            main: `testing used_variables_throw_with_underscore
+            func main(a: Int) -> Int {
+                _ = 1;
+                _thing = 2;
+                a + _thing
+            }`,
+            inputs: [int(1)],
+            output: int(1)
+        },
         {
             description: "rhs enum variant only can be checked",
             main: `testing check_enum_variant