Allow any Ident when parsing asm block instruction opcodes (FuelL…

…abs#4431)

## Description
The idea is to not check for Sway keywords when parsing the opcodes in
`asm` blocks. This is important because some Sway keywords, such as
`mod`, are also FuelVM opcodes. Note that the validity of the opcodes
are later checked anyways so we're not losing any useful checks here.

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

sway-parse/src/expr/asm.rs

@@ -49,7 +49,15 @@ impl ParseToEnd for AsmBlockContents {
             if let Some(consumed) = parser.check_empty() {
                 break (None, consumed);
             }
-            let ident = parser.parse()?;
+
+            // Parse the opcode directly instead of calling `parser.parse()` to avoid checking for
+            // illegal identifiers such as keywords. opcode names should not be subject to those
+            // checks because some opcodes, such as `mod`, are also Sway keywords.
+            let ident = match parser.take::<Ident>() {
+                Some(ident) => ident,
+                None => return Err(parser.emit_error(ParseErrorKind::ExpectedIdent)),
+            };
+
             if let Some(consumed) = parser.check_empty() {
                 let final_expr = AsmFinalExpr {
                     register: ident,

test/src/e2e_vm_tests/test_programs/should_fail/unrecognized_opcode/Forc.lock

@@ -0,0 +1,3 @@
+[[package]]
+name = 'unrecognized_opcode'
+source = 'member'

test/src/e2e_vm_tests/test_programs/should_fail/unrecognized_opcode/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+license = "Apache-2.0"
+implicit-std = false
+name = "unrecognized_opcode"
+entry = "main.sw"
+
+[dependencies]

test/src/e2e_vm_tests/test_programs/should_fail/unrecognized_opcode/src/main.sw

@@ -0,0 +1,8 @@
+script;
+
+fn main() {
+    let _x = asm (r1, r2: 0, r3: 0) {
+        modd r1 r2 r3;
+        r1: u64
+    };
+}

test/src/e2e_vm_tests/test_programs/should_fail/unrecognized_opcode/test.toml

@@ -0,0 +1,4 @@
+category = "fail"
+
+ # check: $()modd r1 r2 r3;
+ # check: $()Unrecognized op code.

test/src/e2e_vm_tests/test_programs/should_pass/language/asm_expr_basic/Forc.toml

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

test/src/e2e_vm_tests/test_programs/should_pass/language/asm_expr_basic/src/main.sw

@@ -16,12 +16,8 @@ struct GasCounts {
 
 fn get_gas() -> GasCounts {
     GasCounts {
-        global_gas: asm() {
-            ggas
-        },
-        context_gas: asm() {
-            cgas
-        }
+        global_gas: asm() { ggas },
+        context_gas: asm() { cgas },
     }
 }
 
@@ -66,5 +62,10 @@ fn main() -> u32 {
 
     let _flag = asm() { flag };
 
+    let _x = asm(r1, r2: 2, r3: 1) {
+        mod  r1 r2 r3;
+        r1: u64
+    };
+
     return 6u32;
 }