Smartpaste isn't smart when pasting indented blocks with cursor.X > 0

[Andriamanitra]

Description of the problem or steps to reproduce

When pasting indented code block such as

    if (1) {
        printf("Hello world\n");
    }

with setlocal smartpaste on micro formats it like this:

    // (paste happens at the same indent level as this comment)
    // if you selected the leading whitespace on the first line:
        if (1) {
        printf("Hello world\n");
    }
    // and if you didn't select the leading whitespace on the first line:
    if (1) {
            printf("Hello world\n");
        }

Note that the problem only happens when cursor is not at X=0 (no indent).

Asciinema demonstration

Current behavior on the left pane, my attempt at fixing some of it on the right:
https://asciinema.org/a/617870 (problems start at 00:30)
The version used on the recording is not the latest but I checked that the behavior hasn't changed since 2.0.12

test file used on the recording

def f():
    if x:
        print("    hello")

# Happy cases:
# 1) Paste block with no indent when cursor.X > 0

# 2) Paste indented block when cursor.X = 0

# 3) Single line with leading spaces


def f() {
    if x {
        ABC
    }
}
# Problematic cases:
# 1) Paste indented block when cursor.X > 0

# 2) Non-matching indentation

# 3) Paste decreasing indentation when cursor.X > 0


# Unsolvable(?) edge cases:
# 1) paste poorly selected (no indent on first line) when cursor.X = 0

# 2) paste poorly selected (no indent on first line) when cursor.X > 0

Version info

Commit hash: d8e9d61
OS: Linux (OpenSUSE Tumbleweed)
Terminal: terminator

The first case seems to be fixed now, but the second case still happens:

Coping this text, with the first selected character as f:

	for i {
		print(i)
	}

And pasting when X != 0 will result in this:

	// existing code
	for i {
			print(i)
		}

[JoeKar]

We discussed about it in #3002 (comment).
There was no simple and smart solution so far.