Explicit a few more types

To avoid that a change in the types of the underlying called functions would result not in a compilation error but instead an incorrect `expect`.

diesel/src/pg/connection/result.rs

@@ -108,9 +108,10 @@ impl PgResult {
     }
 
     pub(super) fn num_rows(&self) -> usize {
-        self.row_count
-            .try_into()
-            .expect("Diesel expects to run on at a least 32 bit OS")
+        self.row_count.try_into().expect(
+            "Diesel expects to run on a >= 32 bit OS \
+                (or libpq is giving out negative row count)",
+        )
     }
 
     pub(super) fn get_row(self: Rc<Self>, idx: usize) -> PgRow {
@@ -149,7 +150,7 @@ impl PgResult {
     }
 
     pub(in crate::pg) fn column_type(&self, col_idx: usize) -> NonZeroU32 {
-        let col_idx = col_idx
+        let col_idx: i32 = col_idx
             .try_into()
             .expect("Column indices are expected to fit into 32 bit");
         let type_oid = unsafe { PQftype(self.internal_result.as_ptr(), col_idx) };
@@ -191,9 +192,10 @@ impl PgResult {
     }
 
     pub(super) fn column_count(&self) -> usize {
-        self.column_count
-            .try_into()
-            .expect("Diesel expects to run on a at least 32 bit OS")
+        self.column_count.try_into().expect(
+            "Diesel expects to run on a >= 32 bit OS \
+                (or libpq is giving out negative column count)",
+        )
     }
 }
 

diesel/src/pg/connection/stmt/mod.rs

@@ -36,7 +36,7 @@ impl Statement {
             .map(|data| data.as_ref().map(|d| d.len().try_into()).unwrap_or(Ok(0)))
             .collect::<Result<Vec<_>, _>>()
             .map_err(|e| crate::result::Error::SerializationError(Box::new(e)))?;
-        let param_count = params_pointer
+        let param_count: libc::c_int = params_pointer
             .len()
             .try_into()
             .map_err(|e| crate::result::Error::SerializationError(Box::new(e)))?;
@@ -71,7 +71,7 @@ impl Statement {
             .map_err(|e| crate::result::Error::SerializationError(Box::new(e)))?;
 
         let internal_result = unsafe {
-            let param_count = param_types
+            let param_count: libc::c_int = param_types
                 .len()
                 .try_into()
                 .map_err(|e| crate::result::Error::SerializationError(Box::new(e)))?;

diesel/src/sqlite/connection/raw.rs

@@ -420,7 +420,7 @@ where
     static NULL_CTX_ERR: &str =
         "We've written the aggregator to the aggregate context, but it could not be retrieved.";
 
-    let n_bytes = std::mem::size_of::<OptionalAggregator<A>>()
+    let n_bytes: i32 = std::mem::size_of::<OptionalAggregator<A>>()
         .try_into()
         .expect("Aggregate context should be larger than 2^32");
     let aggregate_context = unsafe {
@@ -525,7 +525,7 @@ extern "C" fn run_aggregator_final_function<ArgsSqlType, RetSqlType, Args, Ret,
 }
 
 unsafe fn context_error_str(ctx: *mut ffi::sqlite3_context, error: &str) {
-    let len = error
+    let len: i32 = error
         .len()
         .try_into()
         .expect("Trying to set a error message with more than 2^32 byte is not supported");