S. R. Faruqi:

Because of the heart's confinement/compression, and also because of the aspect of the similitude, he gives for the heart the simile of a bud. Mir has often taken advantage of this; for example, see

{138,1}.

But in the present verse, there are layer upon layer of subtleties. In the season of autumn (that is, perhaps, in the season of separation), the heart was confined like a bud. But since the bud is closed like a fist-- that is, its petals are joined to each other-- this was one form of composure/collectedness (confidence, peace). When spring came, then the bud bloomed/opened. But it's clear that by the heart's blossoming/opening nothing else could be meant, except that the heart would open like a wound, or that the heart's wounds would again become fresh.

We can read the second line in two ways. One way is to assume an izafat between bahaar and gul , and give a pause after za;xm . That is, 'How can I sufficiently praise the 'springtime' [flourishing] of the wound-- all I can do is say that it blossomed'. The second way is to give a pause after bahaar . That is, 'Bravo, what a spring it is, how can I sufficiently praise the spring, I can only say that the flower of the wound blossomed'. In both cases, ai remains an expression of praise, not a vocative. Mir has used ai as an expression of praise previously as well: see

{124,2}.

Because they have not recognized ai as an expression of praise, Simab Akbarabadi in dastuur ul-i.slaa;h and Abr Ahsani in i.slaa;h ul-i.slaah have fallen into error. There's a verse of Shahir Machhlishahri:

sho;xii-e raftaar-e naaz ai fitnah-qaamat dekhnaa
;Thokare;N khaatii hai u;Thne par qiyaamat dekhnaa

[the mischievousness of the coquettish gait-- bravo, turmoil-stature, just look at it!
it stumbles when it arises-- look, a Doomsday!]

Munir Shikohabadi has given 'correction' to this, but he has allowed the word ai to remain. At this Simab objected that if ai were removed from the first line, then the line would become trimmer. Abr Ahsani took up the cudgels in reply: a vocative marker is necessary. It's very clear that in Shahir's verse the ai is an exclamation of praise, not a vocative marker. Munir Shikohabadi was an accomplished Ustad; he left it alone because he considered it suitable and correct. Simab and Abr Ahsani both turned out to be in error: they hadn't even understood the subtleties of the usage of the word.

A final point is that the construction gul-e za;xm is utterly supreme. A wound is red, and the flower too is red. For a wound to open is also called the 'blossoming of the wound'. On the basis of these facts, greater beauty has been added to the construction.

FWP:

SETS == EXCLAMATION; IZAFAT
MOTIFS == SPRINGTIME
NAMES
TERMS

There's also a paradoxicalness, a perverse twisting of the expected pattern of imagery: here the bud is associated with autumn, not spring (and thus its 'composure' has a death-like feeling). Elsewhere, in a famous verse, Mir plays the same kind of trick: he associates old age with day and youthfulness with night:

{7,2}.

Using the idiomatic ke rango;N to mean 'like' also serves to remind us of the color differentiation between autumn and spring.

In the second line bahaar seems to me to stand grammatically isolated, as a third brief exclamation. Despite SRF's explanation of the izafat possibility, to say that the 'springtime' 'blossomed' is, in terms of normal Urdu usage, very awkward. Of course, if we had no choice we could do it, but in this case we have a clear (non-izafat) choice all ready for us and very attractive; as an additional hint in its favor, it corresponds to the (very quasi) quasi-caesura in the middle of the line.

Note for spelling fans: Under most circumstances it would be hard to tell khilnaa from khulnaa , which can be synonymous when applied to the blossoming or 'opening' of a flower. But in this case, the ghazal's rhyme-words eliminate the latter reading.