From 11c81b32f8a279dcc59239150cdea3fe4f75cf42 Mon Sep 17 00:00:00 2001
From: Lars Reimann <mail@larsreimann.com>
Date: Sun, 5 May 2024 11:37:29 +0200
Subject: [PATCH] feat: suggest adding assignment if statement does nothing
 (#1156)

Closes #1142

### Summary of Changes

Suggest adding an assignment if the user likely forgot it.
---
 .../validation/other/statements/statements.ts | 28 +++++++++++++++----
 .../has no effect/main.sdsdev                 | 26 ++++++++---------
 2 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/packages/safe-ds-lang/src/language/validation/other/statements/statements.ts b/packages/safe-ds-lang/src/language/validation/other/statements/statements.ts
index 689bb8bf7..438b1483f 100644
--- a/packages/safe-ds-lang/src/language/validation/other/statements/statements.ts
+++ b/packages/safe-ds-lang/src/language/validation/other/statements/statements.ts
@@ -1,18 +1,34 @@
-import { SdsStatement } from '../../../generated/ast.js';
+import { isSdsExpressionStatement, SdsStatement } from '../../../generated/ast.js';
 import { ValidationAcceptor } from 'langium';
 import { SafeDsServices } from '../../../safe-ds-module.js';
+import { NamedTupleType } from '../../../typing/model.js';
 
 export const CODE_STATEMENT_HAS_NO_EFFECT = 'statement/has-no-effect';
 
 export const statementMustDoSomething = (services: SafeDsServices) => {
     const purityComputer = services.purity.PurityComputer;
+    const typeComputer = services.typing.TypeComputer;
 
     return (node: SdsStatement, accept: ValidationAcceptor): void => {
-        if (!purityComputer.statementDoesSomething(node)) {
-            accept('warning', 'This statement does nothing.', {
-                node,
-                code: CODE_STATEMENT_HAS_NO_EFFECT,
-            });
+        if (purityComputer.statementDoesSomething(node)) {
+            return;
         }
+
+        // Special warning message if an assignment is probably missing
+        if (isSdsExpressionStatement(node)) {
+            const expressionType = typeComputer.computeType(node.expression);
+            if (!(expressionType instanceof NamedTupleType) || expressionType.length > 0) {
+                accept('warning', 'This statement does nothing. Did you forget the assignment?', {
+                    node,
+                    code: CODE_STATEMENT_HAS_NO_EFFECT,
+                });
+                return;
+            }
+        }
+
+        accept('warning', 'This statement does nothing.', {
+            node,
+            code: CODE_STATEMENT_HAS_NO_EFFECT,
+        });
     };
 };
diff --git a/packages/safe-ds-lang/tests/resources/validation/other/statements/expression statements/has no effect/main.sdsdev b/packages/safe-ds-lang/tests/resources/validation/other/statements/expression statements/has no effect/main.sdsdev
index 5dcf20fe1..39d35aa38 100644
--- a/packages/safe-ds-lang/tests/resources/validation/other/statements/expression statements/has no effect/main.sdsdev	
+++ b/packages/safe-ds-lang/tests/resources/validation/other/statements/expression statements/has no effect/main.sdsdev	
@@ -4,17 +4,17 @@ package tests.validation.other.statements.expressionStatements.hasNoEffect
 fun impureFunction()
 
 @Pure
-fun pureFunction() -> a: Int
+fun pureFunctionWithResults() -> a: Int
 
 class MyClass() {
     @Impure([ImpurityReason.Other])
     fun impureFunction()
 
-    @Pure fun pureFunction()
+    @Pure fun pureFunctionWithoutResults()
 }
 
 segment pureSegment() {
-    val a = pureFunction();
+    val a = pureFunctionWithResults();
 }
 
 segment impureSegment() {
@@ -30,12 +30,12 @@ segment recursiveB() {
 }
 
 segment mySegment() {
-    // $TEST$ warning "This statement does nothing."
+    // $TEST$ warning "This statement does nothing. Did you forget the assignment?"
     »1 + 2;«
+    // $TEST$ warning "This statement does nothing. Did you forget the assignment?"
+    »pureFunctionWithResults();«
     // $TEST$ warning "This statement does nothing."
-    »pureFunction();«
-    // $TEST$ warning "This statement does nothing."
-    »MyClass().pureFunction();«
+    »MyClass().pureFunctionWithoutResults();«
 
     // $TEST$ no warning "This statement does nothing."
     »impureFunction();«
@@ -43,12 +43,12 @@ segment mySegment() {
     »MyClass().impureFunction();«
 
     () {
-        // $TEST$ warning "This statement does nothing."
+        // $TEST$ warning "This statement does nothing. Did you forget the assignment?"
         »1 + 2;«
+        // $TEST$ warning "This statement does nothing. Did you forget the assignment?"
+        »pureFunctionWithResults();«
         // $TEST$ warning "This statement does nothing."
-        »pureFunction();«
-        // $TEST$ warning "This statement does nothing."
-        »MyClass().pureFunction();«
+        »MyClass().pureFunctionWithoutResults();«
 
         // $TEST$ no warning "This statement does nothing."
         »impureFunction();«
@@ -64,8 +64,8 @@ segment mySegment() {
 
     // $TEST$ warning "This statement does nothing."
     »(() {
-        pureFunction();
-        MyClass().pureFunction();
+        pureFunctionWithResults();
+        MyClass().pureFunctionWithoutResults();
     })();«
 
     // $TEST$ no warning "This statement does nothing."