Add regression tests for sqlite explain

[0rvar]

Original: Fix SQLx+Sqlite incorrectly inferring column as nullable when using ORDER BY and LIMIT in the same query

• Issue reproduction repo: https://github.com/0rvar/sqlx-sqlite-option-repro
• Issue introduced in PR Improve Sqlite support for sub-queries and CTE's #1816

Status: added a failing test, reading through the opcode state machine in explain.
Tips and ideas are appreciated.

Related:

• sqlx::query!(..) inferring wrong Option NULLable-types  #1852

Semi-related:

• [query_as!] Incorrect nullability inferred on left join leading to a runtime exception #2127
• query_as! offline mode mismatched types expected struct X, found enum std::option::Option #1294

It seems the original issue was already fixed in 0.7-dev.
I changed this PR to add more tests for the issues in 0.6 if they are of interest - otherwise, feel free to just close this.

[0rvar]

Some opcodes for reference

sqlite> explain select accounts.name from accounts;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     8     0                    0   Start at 8
1     OpenRead       0     6     0     2              0   root=6 iDb=0; accounts
2     Explain        2     0     0     SCAN accounts  0
3     Rewind         0     7     0                    0
4       Column         0     1     1                    0   r[1]=accounts.name
5       ResultRow      1     1     0                    0   output=r[1]
6     Next           0     4     0                    1
7     Halt           0     0     0                    0
8     Transaction    0     0     20    0              1   usesStmtJournal=0
9     Goto           0     1     0                    0

==========================================================================================

sqlite> explain select accounts.name from accounts ORDER BY accounts.name;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     16    0                    0   Start at 16
1     SorterOpen     1     3     0     k(1,B)         0
2     OpenRead       0     6     0     2              0   root=6 iDb=0; accounts
3     Explain        3     0     0     SCAN accounts  0
4     Rewind         0     9     0                    0
5       Column         0     1     1                    0   r[1]=accounts.name
6       MakeRecord     1     1     3                    0   r[3]=mkrec(r[1])
7       SorterInsert   1     3     1     1              0   key=r[3]
8     Next           0     5     0                    1
9     OpenPseudo     2     4     3                    0   3 columns in r[4]
10    SorterSort     1     15    0                    0
11      SorterData     1     4     2                    0   r[4]=data
12      Column         2     0     2                    0   r[2]=accounts.name
13      ResultRow      2     1     0                    0   output=r[2]
14    SorterNext     1     11    0                    0
15    Halt           0     0     0                    0
16    Transaction    0     0     20    0              1   usesStmtJournal=0
17    Goto           0     1     0                    0

==========================================================================================

sqlite> explain select accounts.name from accounts LIMIT 1;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     10    0                    0   Start at 10
1     Integer        1     1     0                    0   r[1]=1; LIMIT counter
2     OpenRead       0     6     0     2              0   root=6 iDb=0; accounts
3     Explain        3     0     0     SCAN accounts  0
4     Rewind         0     9     0                    0
5       Column         0     1     2                    0   r[2]=accounts.name
6       ResultRow      2     1     0                    0   output=r[2]
7       DecrJumpZero   1     9     0                    0   if (--r[1])==0 goto 9
8     Next           0     5     0                    1
9     Halt           0     0     0                    0
10    Transaction    0     0     20    0              1   usesStmtJournal=0
11    Goto           0     1     0                    0

==========================================================================================

sqlite> explain select accounts.name from accounts ORDER BY accounts.name LIMIT 1;
addr  opcode         p1    p2    p3    p4             p5  comment
----  -------------  ----  ----  ----  -------------  --  -------------
0     Init           0     20    0                    0   Start at 20
1     OpenEphemeral  1     3     0     k(1,B)         0   nColumn=3
2     Integer        1     1     0                    0   r[1]=1; LIMIT counter
3     OpenRead       0     6     0     2              0   root=6 iDb=0; accounts
4     Explain        4     0     0     SCAN accounts  0
5     Rewind         0     15    0                    0
6       Column         0     1     2                    0   r[2]=accounts.name
7       Sequence       1     3     0                    0   r[3]=cursor[1].ctr++
8       IfNotZero      1     12    0                    0   if r[1]!=0 then r[1]--, goto 12
9       Last           1     0     0                    0
10      IdxLE          1     14    2     1              0   key=r[2]
11      Delete         1     0     0                    0
12      MakeRecord     2     2     5                    0   r[5]=mkrec(r[2..3])
13      IdxInsert      1     5     2     2              0   key=r[5]
14    Next           0     6     0                    1
15    Sort           1     19    0                    0
16      Column         1     0     4                    0   r[4]=accounts.name
17      ResultRow      4     1     0                    0   output=r[4]
18    Next           1     16    0                    0
19    Halt           0     0     0                    0
20    Transaction    0     0     20    0              1   usesStmtJournal=0
21    Goto           0     1     0                    0

[tyrelr]

Just as a heads up, you may want to base your pull request off of the "0.7-dev" branch instead of main. Changes to type-inference are delayed until the next minor version, rather than a bugfix release. And there is at least one fix for 'order by' type inference in that branch already.

[0rvar]

@tyrelr well, it seems to be fixed in 0.7-dev. That's great news.
I'll add some more tests from the related issues I linked, maybe this PR will just be about adding some more tests in the end.
Thanks for pointing this out.

[abonander]

@0rvar can you rebase?

[0rvar]

@abonander I now have capacity to rebase this, if you're still interested. Let me know