Add STYLEGUIDE.md on our development practices

CONTRIBUTING.md

@@ -197,43 +197,7 @@ that are missing in earlier minor versions.
 
 ### Following our coding conventions
 
-CI pipeline will automatically reject any PRs which do not follow our coding
-conventions. The easiest way to ensure your PR adheres to those conventions is
-to use the [citus_indent](https://github.com/citusdata/tools/tree/develop/uncrustify)
-tool. This tool uses `uncrustify` under the hood.
-
-```bash
-# Uncrustify changes the way it formats code every release a bit. To make sure
-# everyone formats consistently we use version 0.68.1:
-curl -L https://github.com/uncrustify/uncrustify/archive/uncrustify-0.68.1.tar.gz | tar xz
-cd uncrustify-uncrustify-0.68.1/
-mkdir build
-cd build
-cmake ..
-make -j5
-sudo make install
-cd ../..
-
-git clone https://github.com/citusdata/tools.git
-cd tools
-make uncrustify/.install
-```
-
-Once you've done that, you can run the `make reindent` command from the top
-directory to recursively check and correct the style of any source files in the
-current directory. Under the hood, `make reindent` will run `citus_indent` and
-some other style corrections for you.
-
-You can also run the following in the directory of this repository to
-automatically format all the files that you have changed before committing:
-
-```bash
-cat > .git/hooks/pre-commit << __EOF__
-#!/bin/bash
-citus_indent --check --diff || { citus_indent --diff; exit 1; }
-__EOF__
-chmod +x .git/hooks/pre-commit
-```
+Our coding conventions are documented in [STYLEGUIDE.md](STYLEGUIDE.md).
 
 ### Making SQL changes
 
@@ -292,3 +256,28 @@ See [`src/test/regress/README.md`](https://github.com/citusdata/citus/blob/maste
 User-facing documentation is published on [docs.citusdata.com](https://docs.citusdata.com/). When adding a new feature, function, or setting, you can open a pull request or issue against the [Citus docs repo](https://github.com/citusdata/citus_docs/).
 
 Detailed descriptions of the implementation for Citus developers are provided in the [Citus Technical Documentation](src/backend/distributed/README.md). It is currently a single file for ease of searching. Please update the documentation if you make any changes that affect the design or add major new features.
+
+# Making a pull request ready for reviews
+
+Asking for help and asking for reviews are two different things. When you're asking for help, you're asking for someone to help you with something that you're not expected to know.
+
+But when you're asking for a review, you're asking for someone to review your work and provide feedback. So, when you're asking for a review, you're expected to make sure that:
+
+* Your changes don't perform **unnecessary line addition / deletions / style changes on unrelated files / lines**.
+
+* All CI jobs are **passing**, including **style checks** and **flaky test detection jobs**. Note that if you're an external contributor, you don't have to wait CI jobs to run (and finish) because they don't get automatically triggered for external contributors.
+
+* Your PR has necessary amount of **tests** and that they're passing.
+
+* You separated as much as possible work into **separate PRs**, e.g., a prerequisite bugfix, a refactoring etc..
+
+* Your PR doesn't introduce a typo or something that you can easily fix yourself.
+
+* After all CI jobs pass, code-coverage measurement job (CodeCov as of today) then kicks in. That's why it's important to make the **tests passing** first. At that point, you're expected to check **CodeCov annotations** that can be seen in the **Files Changed** tab and expected to make sure that it doesn't complain about any lines that are not covered. For example, it's ok if CodeCov complains about an `ereport()` call that you put for an "unexpected-but-better-than-crashing" case, but it's not ok if it complains about an uncovered `if` branch that you added.
+
+* And finally, perform a **self-review** to make sure that:
+  * Code and code-comments reflects the idea **without requiring an extra explanation** via a chat message / email / PR comment.
+    This is important because we don't expect developers to reach out to author / read about the whole discussion in the PR to understand the idea behind a commit merged into `main` branch.
+  * PR description is clear enough.
+  * If-and-only-if you're **introducing a user facing change / bugfix**, your PR has a line that starts with `DESCRIPTION: <Present simple tense word that starts with a capital letter, e.g., Adds support for / Fixes / Disallows>`.
+  * **Commit messages** are clear enough if the commits are doing logically different things.

STYLEGUIDE.md

@@ -0,0 +1,160 @@
+# Coding style
+
+The existing code-style in our code-base is not super consistent. There are multiple reasons for that. One big reason is because our code-base is relatively old and our standards have changed over time. The second big reason is that our style-guide is different from style-guide of Postgres and some code is copied from Postgres source code and is slightly modified. The below rules are for new code. If you're changing existing code that uses a different style, use your best judgement to decide if you use the rules here or if you match the existing style.
+
+## Using citus_indent
+
+CI pipeline will automatically reject any PRs which do not follow our coding
+conventions. The easiest way to ensure your PR adheres to those conventions is
+to use the [citus_indent](https://github.com/citusdata/tools/tree/develop/uncrustify)
+tool. This tool uses `uncrustify` under the hood.
+
+```bash
+# Uncrustify changes the way it formats code every release a bit. To make sure
+# everyone formats consistently we use version 0.68.1:
+curl -L https://github.com/uncrustify/uncrustify/archive/uncrustify-0.68.1.tar.gz | tar xz
+cd uncrustify-uncrustify-0.68.1/
+mkdir build
+cd build
+cmake ..
+make -j5
+sudo make install
+cd ../..
+
+git clone https://github.com/citusdata/tools.git
+cd tools
+make uncrustify/.install
+```
+
+Once you've done that, you can run the `make reindent` command from the top
+directory to recursively check and correct the style of any source files in the
+current directory. Under the hood, `make reindent` will run `citus_indent` and
+some other style corrections for you.
+
+You can also run the following in the directory of this repository to
+automatically format all the files that you have changed before committing:
+
+```bash
+cat > .git/hooks/pre-commit << __EOF__
+#!/bin/bash
+citus_indent --check --diff || { citus_indent --diff; exit 1; }
+__EOF__
+chmod +x .git/hooks/pre-commit
+```
+
+## Other rules we follow that citus_indent does not enforce
+
+* We almost always use **CamelCase**, when naming functions, variables etc., **not snake_case**.
+
+* We also have the habits of using a **lowerCamelCase** for some variables named from their type or from their function name, as shown in the examples:
+
+  ```c
+  bool IsCitusExtensionLoaded = false;
+
+
+  bool
+  IsAlterTableRenameStmt(RenameStmt *renameStmt)
+  {
+    AlterTableCmd *alterTableCommand = NULL;
+    ..
+    ..
+
+    bool isAlterTableRenameStmt = false;
+    ..
+  }
+  ```
+
+* We **start functions with a comment**:
+
+  ```c
+  /*
+   * MyNiceFunction <something in present simple tense, e.g., processes / returns / checks / takes X as input / does Y> ..
+   * <some more nice words> ..
+   * <some more nice words> ..
+   */
+  <static?> <return type>
+  MyNiceFunction(..)
+  {
+    ..
+    ..
+  }
+  ```
+
+* `#includes` needs to be sorted based on below ordering and then alphabetically and we should not include what we don't need in a file:
+
+  * System includes (eg. #include<...>)
+  * Postgres.h (eg. #include "postgres.h")
+  * Toplevel imports from postgres, not contained in a directory (eg. #include "miscadmin.h")
+  * General postgres includes (eg . #include "nodes/...")
+  * Toplevel citus includes, not contained in a directory (eg. #include "citus_verion.h")
+  * Columnar includes (eg. #include "columnar/...")
+  * Distributed includes (eg. #include "distributed/...")
+
+* Comments:
+  ```c
+  /* single line comments start with a lower-case */
+
+  /*
+   * We start multi-line comments with a capital letter
+   * and keep adding a star to the beginning of each line
+   * until we close the comment with a star and a slash.
+   */
+  ```
+
+* Order of function implementations and their declarations in a file:
+
+  We define static functions after the functions that call them. For example:
+
+  ```c
+  #include<..>
+  #include<..>
+  ..
+  ..
+  typedef struct
+  {
+    ..
+    ..
+  } MyNiceStruct;
+  ..
+  ..
+  PG_FUNCTION_INFO_V1(my_nice_udf1);
+  PG_FUNCTION_INFO_V1(my_nice_udf2);
+  ..
+  ..
+  // ..  somewhere on top of the file …
+  static void MyNiceStaticlyDeclaredFunction1(…);
+  static void MyNiceStaticlyDeclaredFunction2(…);
+  ..
+  ..
+
+
+  void
+  MyNiceFunctionExternedViaHeaderFile(..)
+  {
+    ..
+    ..
+    MyNiceStaticlyDeclaredFunction1(..);
+    ..
+    ..
+    MyNiceStaticlyDeclaredFunction2(..);
+    ..
+  }
+
+  ..
+  ..
+
+  // we define this first because it's called by MyNiceFunctionExternedViaHeaderFile()
+  // before MyNiceStaticlyDeclaredFunction2()
+  static void
+  MyNiceStaticlyDeclaredFunction1(…)
+  {
+  }
+  ..
+  ..
+
+  // then we define this
+  static void
+  MyNiceStaticlyDeclaredFunction2(…)
+  {
+  }
+  ```

src/test/regress/README.md

@@ -165,3 +165,14 @@ help cleaning up in the future.
 
 In CI sometimes a test fails randomly, we call these tests "flaky". To fix these
 flaky tests see [`src/test/regress/flaky_tests.md`](https://github.com/citusdata/citus/blob/main/src/test/regress/flaky_tests.md)
+
+# Regression test best practices
+
+* Instead of connecting to different nodes to check catalog tables, should use `run_command_on_all_nodes()` because it's faster than keep disconnecting / connecting to different nodes.
+
+* Tests should **define functions** for repetitive actions, e.g., by wrapping usual queries used to check catalog tables.
+  If the function is presumed to be used by other tests in future, then the function needs to defined in `multi_test_helpers.sql`.
+
+* If you're adding a new file, consider using `src/test/regress/bin/create_test.py your_new_test_name` to create the file. Or if you want to manually create it, make sure that your test file creates a schema and that it drops the schema at the end of the test to make sure that it doesn't leak any objects behind. See which lines `src/test/regress/bin/create_test.py` adds to the test file to understand what you need to do.
+
+  For the object that are not bound to a schema, make sure to drop them at the end of the test too, such as databases and roles.