Improve warnings on unnecessary storage annotations (FuelLabs#3414)

Fixes FuelLabs#1183: just trying to improve the error message.

This PR also provides a fix for the following issue: the purity analyzer
did not report the case where *both* read and write storage annotations
were unused, i.e. in this case there were no warnings:

```
contract;

abi MyContract {
    #[storage(read, write)]
    fn foo() -> u64;
}

impl MyContract for Contract {
    #[storage(read, write)]
    fn foo() -> u64 {
        0
    }
}
```

sway-core/src/ir_generation/purity.rs

@@ -118,11 +118,15 @@ pub(crate) fn check_function_purity(
         // Or we have unneeded attributes.
         (Some(StorageOperation::ReadsWrites), false, true) => warn(span, Reads),
         (Some(StorageOperation::ReadsWrites), true, false) => warn(span, Writes),
+        (Some(StorageOperation::ReadsWrites), false, false) => warn(span, ReadsWrites),
         (Some(StorageOperation::Reads), false, false) => warn(span, Reads),
         (Some(StorageOperation::Writes), false, false) => warn(span, Writes),
 
-        // (Pure, false, false) is OK, as is (ReadsWrites, true, true).
-        _ => (),
+        // Attributes and effects are in total agreement
+        (None, false, false)
+        | (Some(StorageOperation::Reads), true, false)
+        | (Some(StorageOperation::Writes), false, true)
+        | (Some(StorageOperation::ReadsWrites), true, true) => (),
     };
 
     (reads, writes)

sway-error/src/warning.rs

@@ -217,8 +217,8 @@ impl fmt::Display for Warning {
             ),
             DeadStorageDeclarationForFunction { unneeded_attrib } => write!(
                 f,
-                "The '{unneeded_attrib}' storage declaration for this function is never accessed \
-                and can be removed."
+                "This function's storage attributes declaration does not match its \
+                 actual storage access pattern: '{unneeded_attrib}' attribute(s) can be removed."
             ),
             MatchExpressionUnreachableArm => write!(f, "This match arm is unreachable."),
             UnrecognizedAttribute {attrib_name} => write!(f, "Unknown attribute: \"{attrib_name}\"."),

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = 'core'
+source = 'path+from-root-B415B1E0A318C0B0'
+
+[[package]]
+name = 'std'
+source = 'path+from-root-B415B1E0A318C0B0'
+dependencies = ['core']
+
+[[package]]
+name = 'storage_annotations_unused_read'
+source = 'member'
+dependencies = ['std']

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+name = "storage_annotations_unused_read"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+
+[dependencies]
+std = { path = "../../../../../../../sway-lib-std" }

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read/src/main.sw

@@ -0,0 +1,13 @@
+contract;
+
+abi MyContract {
+    #[storage(read)]
+    fn foo() -> u64;
+}
+
+impl MyContract for Contract {
+    #[storage(read)]
+    fn foo() -> u64 {
+        0
+    }
+}

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read/test.toml

@@ -0,0 +1,3 @@
+category = "compile"
+
+# check: $()This function's storage attributes declaration does not match this function's actual storage access pattern: 'read' attribute(s) can be removed.

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read_and_write/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = 'core'
+source = 'path+from-root-F9F255B625A3400C'
+
+[[package]]
+name = 'std'
+source = 'path+from-root-F9F255B625A3400C'
+dependencies = ['core']
+
+[[package]]
+name = 'storage_annotations_unused_read_and_write'
+source = 'member'
+dependencies = ['std']

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read_and_write/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+name = "storage_annotations_unused_read_and_write"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+
+[dependencies]
+std = { path = "../../../../../../../sway-lib-std" }

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read_and_write/src/main.sw

@@ -0,0 +1,13 @@
+contract;
+
+abi MyContract {
+    #[storage(read, write)]
+    fn foo() -> u64;
+}
+
+impl MyContract for Contract {
+    #[storage(read, write)]
+    fn foo() -> u64 {
+        0
+    }
+}

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_read_and_write/test.toml

@@ -0,0 +1,3 @@
+category = "compile"
+
+# check: $()This function's storage attributes declaration does not match this function's actual storage access pattern: 'read, write' attribute(s) can be removed.

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_write/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = 'core'
+source = 'path+from-root-4A37DED755D546B6'
+
+[[package]]
+name = 'std'
+source = 'path+from-root-4A37DED755D546B6'
+dependencies = ['core']
+
+[[package]]
+name = 'storage_annotations_unused_write'
+source = 'member'
+dependencies = ['std']

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_write/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+name = "storage_annotations_unused_write"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+
+[dependencies]
+std = { path = "../../../../../../../sway-lib-std" }

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_write/src/main.sw

@@ -0,0 +1,13 @@
+contract;
+
+abi MyContract {
+    #[storage(write)] // Or any other storage annotation
+    fn foo() -> u64;
+}
+
+impl MyContract for Contract {
+    #[storage(write)] // Or any other storage annotation
+    fn foo() -> u64 {
+        0
+    }
+}

test/src/e2e_vm_tests/test_programs/should_pass/static_analysis/storage_annotations_unused_write/test.toml

@@ -0,0 +1,3 @@
+category = "compile"
+
+# check: $()This function's storage attributes declaration does not match this function's actual storage access pattern: 'write' attribute(s) can be removed.