Merge 'core: constraint check uniqueness' from Pere Diaz Bou

```bash
limbo> insert into products values (1, 'asdf', 432);
Runtime error: UNIQUE constraint failed: products.id (19)
```

Closes #336

core/error.rs

@@ -36,6 +36,8 @@ pub enum LimboError {
     InvalidTime(String),
     #[error("Modifier parsing error: {0}")]
     InvalidModifier(String),
+    #[error("Runtime error: {0}")]
+    Constraint(String),
 }
 
 #[macro_export]
@@ -51,3 +53,6 @@ macro_rules! bail_corrupt_error {
         return Err($crate::error::LimboError::Corrupt(format!($($arg)*)))
     };
 }
+
+pub const SQLITE_CONSTRAINT: usize = 19;
+pub const SQLITE_CONSTRAINT_PRIMARYKEY: usize = SQLITE_CONSTRAINT | (6 << 8);

core/translate/emitter.rs

@@ -1453,7 +1453,10 @@ fn epilogue(
     start_offset: BranchOffset,
 ) -> Result<()> {
     program.resolve_label(halt_label, program.offset());
-    program.emit_insn(Insn::Halt);
+    program.emit_insn(Insn::Halt {
+        err_code: 0,
+        description: String::new(),
+    });
 
     program.resolve_label(init_label, program.offset());
     program.emit_insn(Insn::Transaction);

core/translate/insert.rs

@@ -4,6 +4,7 @@ use sqlite3_parser::ast::{
     DistinctNames, InsertBody, QualifiedName, ResolveType, ResultColumn, With,
 };
 
+use crate::error::SQLITE_CONSTRAINT_PRIMARYKEY;
 use crate::Result;
 use crate::{
     schema::{Schema, Table},
@@ -167,7 +168,15 @@ pub fn translate_insert(
             },
             make_record_label,
         );
-        program.emit_insn(Insn::Halt); // Add error code 1555 and rollback
+        // TODO: rollback
+        program.emit_insn(Insn::Halt {
+            err_code: SQLITE_CONSTRAINT_PRIMARYKEY,
+            description: format!(
+                "{}.{}",
+                table.get_name(),
+                table.column_index_to_name(0).unwrap()
+            ),
+        });
         program.resolve_label(make_record_label, program.offset());
         program.emit_insn(Insn::MakeRecord {
             start_reg: column_registers_start + 1,
@@ -188,7 +197,10 @@ pub fn translate_insert(
     });
 
     program.resolve_label(halt_label, program.offset());
-    program.emit_insn(Insn::Halt);
+    program.emit_insn(Insn::Halt {
+        err_code: 0,
+        description: String::new(),
+    });
     program.resolve_label(init_label, program.offset());
     program.emit_insn(Insn::Transaction);
     program.emit_constant_insns();

core/translate/mod.rs

@@ -135,7 +135,10 @@ fn translate_pragma(
             todo!()
         }
     };
-    program.emit_insn(Insn::Halt);
+    program.emit_insn(Insn::Halt {
+        err_code: 0,
+        description: String::new(),
+    });
     program.resolve_label(init_label, program.offset());
     program.emit_insn(Insn::Transaction);
     program.emit_constant_insns();

core/vdbe/explain.rs

@@ -383,9 +383,12 @@ pub fn insn_to_str(
                 0,
                 "".to_string(),
             ),
-            Insn::Halt => (
+            Insn::Halt {
+                err_code,
+                description: _,
+            } => (
                 "Halt",
-                0,
+                *err_code as i32,
                 0,
                 0,
                 OwnedValue::Text(Rc::new("".to_string())),

core/vdbe/mod.rs

@@ -23,7 +23,7 @@ pub mod sorter;
 
 mod datetime;
 
-use crate::error::LimboError;
+use crate::error::{LimboError, SQLITE_CONSTRAINT_PRIMARYKEY};
 use crate::function::{AggFunc, FuncCtx, JsonFunc, ScalarFunc};
 use crate::json::get_json;
 use crate::pseudo::PseudoCursor;
@@ -232,7 +232,10 @@ pub enum Insn {
     },
 
     // Halt the program.
-    Halt,
+    Halt {
+        err_code: usize,
+        description: String,
+    },
 
     // Start a transaction.
     Transaction,
@@ -1001,7 +1004,25 @@ impl Program {
                         state.pc += 1;
                     }
                 }
-                Insn::Halt => {
+                Insn::Halt {
+                    err_code,
+                    description,
+                } => {
+                    match *err_code {
+                        0 => {}
+                        SQLITE_CONSTRAINT_PRIMARYKEY => {
+                            return Err(LimboError::Constraint(format!(
+                                "UNIQUE constraint failed: {} (19)",
+                                description
+                            )));
+                        }
+                        _ => {
+                            return Err(LimboError::Constraint(format!(
+                                "undocumented halt error code {}",
+                                description
+                            )));
+                        }
+                    }
                     pager.end_read_tx()?;
                     return Ok(StepResult::Done);
                 }